Método de Falck

En 2007 Falck y col. describieron un método organocatalítico y enantioselectivo para preparar

sin-dioles 1,2- y 1,3- utilizando cetonas α,β-insaturadas.195 _{En este protocolo tiene lugar una} adición de oxi-Michael u oxa-Michael de un ácido hemiéster borónico, formado in situ por el ácido borónico y la δ-hidroxi-α,β-enona, catalizada por una amina terciaria. La versión enantioselectiva de esta reacción utiliza catalizadores bifuncionales quirales del tipo tiourea/amina terciaria. En este caso, la tiourea se coordina con el carbonilo y el nitrógeno de la amina terciaria al boro, facilitando así la adición conjugada. Finalmente, la oxidación del boronato cíclico (1,3-dioxa-2-borinano) con H2O2 permite aislar el diol deseado en buenos rendimientos y excelentes diastereoselectividades.

106

Esquema 7.5. Adición conjugada. Método de Falck

Decidimos probar esta reacción en nuestro modelo del Fragmento Norte 7.5, tanto con una tiourea quiral como con la tiourea aquiral de Schreiner, ya que esperábamos que en la molécula final el hidroxilo en C16 actuara como grupo director en la adición, formándose el diol sin en

C18.

A pesar de conseguir el producto deseado, el rendimiento no fue muy alto en las primeras pruebas, obteniendo mayoritariamente el aducto 7.6.

Se decidió entonces realizar la reacción en dos etapas, aislando el boronato cíclico (el borinano

7.6) con buen rendimiento y estudiando la eliminación del ácido borónico mediante un método

más suave. El método de oxidación puede que no sea óptimo para aplicarlo a la síntesis total de la Anfidinolida B2 en una etapa tan avanzada, ya que la molécula tiene otros grupos funcionales

que pueden reaccionar bajo estas condiciones.

Por ello que se optó por la transesterificación del éster borónico con dioles y aminoalcoholes para formar una especie termodinámicamente más estable y liberar así nuestra molécula. La estabilidad relativa de un gran número de fenilboronatos ya fue estudiada por Brown y col.,

Etapas Finales

107 concluyendo que los cis-1,2-ciclopentanodioles forman fenilboronatos más estables que los boronatos cíclicos de seis miembros, como es nuestro caso.196

Esquema 7.6. Orden de estabilidad termodinámica de boronatos

Este estudio se realizó con 3 equivalentes de los dioles y aminoalcoholes que se observan en el

Esquema 7.7 en CDCl3.

Esquema 7.7. Dioles y aminoalcoholes

Todas las reacciones fueron monitorizadas por RMN de 1_{H cada 5-10 minutos hasta que llegaron} al equilibrio, lo que ocurrió siempre antes de los 20 minutos. En el Esquema 7.8 se pueden apreciar los equilibrios en cada uno de los casos.

108

Como ya habían descrito Brown y col.,196 _{el diol cíclico (cis) resultó el termodinámicamente más} estable, seguido del 1,3-propanodiol. No obstante, no se observó transboronación con el pinacol, a pesar de haberse descrito que sus boronatos son más estables que los boronatos formados con el 1,3-propanodiol.196

Cabe destacar que cuando se utilizó la tiourea de Schreiner se obtuvo una mezcla de diastereómeros en proporción 1:1, mientras que con la tiourea derivada de la cinchona únicamente se observó un diastereómero.

En la misma línea, Helena Mora en su Máster estudió esta reacción con el modelo 7.8 y comprobó que, al contrario de los resultados mostrados por Falck, el ácido fenilborónico (ácido bencenoborónico) daba mejores rendimientos que el ácido 3,4,5-trimetoxifenilborónico (ácido 3,4,5-trimetoxibencenoborónico). Aunque la adición del hemiéster borónico al doble enlace conjugado puede ser más rápida con este último, la formación del hemiéster puede ser más lenta, por lo que al tratarse de un hidroxilo terciario la primera etapa quizás tenga lugar con muy bajo rendimiento. Además, observamos que la tiourea no era necesaria para que la reacción tuviera lugar.

Entrada Ácido borónico Tiourea Rendimiento

1 XXI - 29

2 XXI 0.2 31

3 XXII - 77

4 XXII 0.2 81

Tabla 7.1. Estudios de la reacción de formación del boronato cíclico (Máster de Helena Mora)

Mediante el análisis de los espectros de 1_{H y} 13_{C, H. Mora estimó una relación diastereomérica} aproximada de 80:20 en el nuevo centro creado (ambos como mezcla racémica). Por espectros de NOESY determinó que el diastereómero mayoritario corresponde al diol sin. Estos resultados, aunque sean preliminares y aplicados a modelos sencillos, parecen confirmar que la transformación puede ser aplicada a la síntesis de la Anfidinolida B2.

Experimental Section

I

CAPÍTULO 8

Experimental Section

General Experimental Methods

All reactions were conducted in oven-dried glassware under an inert atmosphere of nitrogen with anhydrous solvents. The solvents and reagents were purified and dried according to standard procedures. Specific rotations were determined at 20°C on a Perkin-Elmer 241 MC polarimeter. IR spectra were recorded on either a Perkin-Elmer 681 or a Nicolet 510 FT spectrometer and only the more representative frequencies (cm–1_{) are reported.} 1_{H NMR (400 MHz) and} 13_{C NMR (100.6 MHz) spectra were recorded on} a Varian Mercury-400 spectrometer. Chemical shifts (δ) are quoted in ppm and referenced to internal TMS (δ 0.00) for 1_{H NMR and CDCl}

3 (δ 77.16) for 13C NMR; coupling constants (J) are quoted in Hz; data are reported as follows: s, singlet; d, doublet; t, triplet; q, quartet; m, multiplet; br, broad; where appropriate, 2D techniques were also used to assist in structure elucidation. High resolution mass spectra (HRMS) were obtained from the Unitat d’Espectrometria de Masses, Serveis Científico-Tècnics de la Universitat de Barcelona. Flash chromatography was performed on Merck silica gel 60 (0.040–0.063 mm). Analytical thin-layer chromatography was carried out on Merck Kieselgel 60 F254 plates.

8.1 Fragment I

(2Z)-3-Iodo-2-buten-1-ol 1.752

A 65% solution of Red-Al in toluene (32.6 mL, 107 mmol) was added dropwise to a stirred solution of 2-butyn-1-ol (5.00 mL, 66.8 mmol) in anhydrous Et2O (67 mL) at 0 °C. After stirring for 4 h at room temperature, the reaction was cooled to 0 °C and quenched by addition of a solution of iodine (51.0 g, 200 mmol) in THF (200 mL). Stirring was continued overnight at room temperature and then a saturated aqueous solution of Na2S2O3 (100 mL) and HCl 2 M (20 mL) were added to the reaction flask and the layers were separated. The aqueous phase was extracted with EtOAc (3 x 30 mL) and the combined organic phases were washed with brine, dried over MgSO4, filtered and concentrated. The reddish residue was purified by flash column chromatography (hexanes/EtOAc, 7:3) to afford 1.7 (9.5 g, 72% yield).

II

Yellow oil; Rf 0.27 (hexanes/EtOAc, 85:15); 1_{H NMR (400 MHz, CDCl3) δ 5.75 (tq,} J = 6.0, 1.5, 1H, H17), 4.17 (dq, J = 6.0, 1.5, 2H, H18), 2.54 (q, J = 1.3, 3H, Me16); 13_{C NMR (100.6 MHz, CDCl3) δ 134.1, 100.0, 67.4, 33.6; IR (film) 3313, 2950, 2911, 2871, 1720,}

1649, 1426, 1375, 1256, 1222, 1073, 1005 cm-1_.

(2Z,4E)-3,4-Dimethyl-5-triisopropylsilyl-2,4-pentadien-1-ol 1.6

A mixture of 1-triisopropylsilyl-1-propyne (3.53 g, 17.9 mmol) and 9-BBN (2.40 g, 19.7 mmol) was stirred for 1 h at 90 °C. It was then allowed to cool to room temperature before adding THF (5 mL) and NaOH 2.0 M (18 mL, 36 mmol). This mixture was then transferred via cannula to a flask containing a solution of vinyl iodide 1.7 (3.20 g, 16.1 mmol) and Pd(PPh3)4 (184 mg, 0.16 mmol) in THF (36 mL). The resulting mixture was then heated at 70 °C for 12 h. The reaction was quenched by addition of 3 M NaOH (7 mL) followed by H2O2 (6 mL). The mixture was diluted with water and extracted with Et2O (3 x 20 mL). The combined organic extracts were dried over MgSO4, filtered and concentrated under reduced pressure. Purification by flash column chromatography (hexanes/EtOAc, 90:10) afforded the desired product 1.6 (3.81 g, 88% yield).

Colorless oil; Rf 0.29 (hexanes/EtOAc, 9:1); 1_{H NMR (400 MHz, CDCl3) δ 5.34}

(t, J = 6.6, 1H, H17), 5.07 (s, 1H, H14), 4.15 (d, J = 6.6, 2H, H18), 1.86 (s, 3H,

Me15), 1.85 (s, 3H, Me16), 1.17 − 1.11 (m, 3H, Si(CH(CH3)2)3), 1.07 − 1.02 (m, 18H, Si(CH(CH3)2)3); 13C NMR (100.6 MHz, CDCl3) δ 154.9, 146.8, 123.2, 122.7, 60.6, 23.0,

22.1, 18.9, 12.3; IR (ATR) 3434, 1721, 1463, 1382, 1086, 1018 cm-1_{; HRMS (ESI+) calcd for} C16H32NaOSi+ _[M+Na]+ _{291.2115, found 291.2115.}

(2R,3S,4E)-2,3-Epoxy-3,4-dimethyl-5-triisopropylsilyl-4-penten-1-ol 1.5

(−)-Diisopropyl tartrate (387 μL, 2.38 mmol), titanium tetraisopropoxide (506 μL, 1.70 mmol) and tert-butyl peroxide (2.77 mL, 25.5 mmol) were added to a suspension of 4 Å molecular sieves (400 mg) in CH2Cl2 (28 mL) at −10 °C. After 10 min at that temperature, the suspension was cooled to −20 °C before the addition of alcohol 1.6 (4.58 g, 17.0 mmol). The resulting mixture was stirred for 45 min at −20 °C and then it was allowed to warm to 0 °C and was monitored by TLC (hexanes/EtOAc, 8:2). When the starting material was completely consumed, the reaction was quenched by addition of water (10 mL) and NaOH 1 M (15 mL) and extracted with CH2Cl2 (3 x 15 mL). The combined organic extracts were dried over MgSO4, filtered

Experimental Section

III and concentrated. The crude oil was purified by flash column chromatography (hexanes/EtOAc, 9:1) to afford the desired product 1.5 (4.65 g, 92% yield).

Colorless oil; Rf 0.36 (hexanes/EtOAc, 8:2); []20

D −12.4 (c 1.1, CHCl3); 1H NMR (400 MHz, CDCl3) δ 5.45 (s, 1H, H14), 3.70 (m, 1H, H18), 3.51 (m, 1H,

H18’), 3.10 (dd, 1H, J = 6.7, 4.3, H17), 1.84 (s, 3H, Me15), 1.57 (m, 1H, OH),

1.46 (s, 3H, Me16), 1.19 − 1.11 (m, 3H, Si(CH(CH3)2)3), 1.05 – 1.03 (m, 18H, Si(CH(CH3)2)3); 13C NMR (100.6 MHz, CDCl3) δ 151.4, 120.6, 66.3, 64.4, 61.9, 22.6, 20.3, 18.6, 11.9; IR (ATR) 3376 (br), 2940, 2890, 2864, 1617, 1458 cm−1_{; HRMS (ESI+) calcd for C16H33O2Si}+ _[M+H]+ _285.2244, found: 285.2243.

(3R,4E)-3,4-Dimethyl-5-triisopropylsilyl-4-pentene-1,3-diol 2.2

A 65% solution of Red-Al in toluene (1.0 mL, 3.1 mmol) was added dropwise to a solution of epoxide 1.5 (735 mg, 2.58 mmol) in THF (25 mL) at 0 °C. After 1 h, an aqueous saturated solution of Rochelle’s salt was added and the mixture was stirred over 1 h. After separating the phases, the aqueous phase was extracted with CH2Cl2 (3 x 10 mL) and the combined organic extracts were dried over MgSO4, filtered and concentrated. Flash column chromatography (hexanes/EtOAc, 7:3) afforded 2.2 (741 mg, 99% yield).

Colorless oil; Rf 0.25 (hexanes/EtOAc, 7:3); 1_{H NMR (400 MHz, CDCl3)} 

5.60 (q, J = 0.8, 1H, H14), 3.77 (t, J = 5.4, 2H, H18), 2.49 (br, 2H, OH), 1.90 (t, J = 5.4, 2H, H17), 1.80 (s, 3H, Me15), 1.37 (s, 3H, Me16), 1.18 – 1.10 (m, 3H, Si(CH(CH3)2)3), 1.07 – 1.05 (m, 18H, Si(CH(CH3)2)3); 13C NMR (100.6 MHz, CDCl3) 159.3,

116.7, 78.5, 60.5, 40.9, 28.9, 22.4, 19.9, 12.4.

(1E,3R)-2,3-Dimethyl-3,5-bis(triethylsilyloxy)-1-triisopropylsilyl-1-pentene 2.6

TESOTf (0.63 mL, 2.78 mmol) was added to a stirred solution of diol 2.2 (363 mg, 1.26 mmol) and 2,6-lutidine (0.56 mL, 3.78 mmol) in CH2Cl2 (13 mL) at 0 °C. After 30 min, water (8 mL) was added, the phases were separated and the aqueous phase was extracted with CH2Cl2 (3 x 6 mL). The combined organic layers were dried over MgSO4, filtered and concentrated. Flash column chromatography (hexanes/EtOAc, 98:2) afforded 2.6 (515 mg, 76% yield).

IV

Colorless oil; Rf 0.69 (hexanes/EtOAc, 7:3); 1_{H NMR (400 MHz, CDCl3)}

 5.54 (s, 1H, H14), 3.65 (ddd, J = 11.2, 10.1, 5.1, 1H, H18), 3.46 (ddd, = 11.2, 10.1, 5.3, 1H, H18’), 1.94 (ddd, J = 12.9, 11.3, 5.3, 1H, H17), 1.83 – 1.78 (m, 1H, H17’), 1.77 (s, 3H, Me15), 1.37 (s, 3H, Me16), 1.19 – 1.08 (m, 3H, Si(CH(CH3)2)3), 1.08 – 1.02 (m, 18H, Si(CH(CH3)2)3), 0.96 (t, J = 7.9, 9H, Si(CH2CH3)3), 0.94 (t, J =

7.9, 9H, Si(CH2CH3)3), 0.61 (q, J = 7.9, 6H, Si(CH2CH3)3), 0.57 (q, J = 7.9, 6H, Si(CH2CH3)3); 13C NMR

(100.6 MHz, CDCl3) 158.9, 116.4, 78.6, 59.8, 44.7, 28.5, 19.6, 19.1, 12.5, 7.4, 7.1, 6.9, 4.5.

(3R,4E)-3,4-Dimethyl-3-triethylsilyloxy-5(triisopropylsilyl)pent-4-enal 2.7

Freshly distilled (COCl)2 (465 μL, 5.42 mmol) was added dropwise to a stirred solution of DMSO (869 μL, 12.2 mmol) in CH2Cl2 at −78 °C. After 10 min, vinylsilane 2.6 (365 mg, 0.68 mmol) in CH2Cl2 (1 mL) was transferred via cannula and the reaction was allowed to warm to −35 °C. After 45 min at this temperature it was cooled to −78 °C and Et3N (2.84 mL, 20.4 mmol) was added dropwise and the reaction was stirred for 2 h at room temperature. It was then diluted with Et2O (5 mL) and the organic extract was washed with saturated NaHCO3 solution (4 mL), dried over MgSO4, filtered and concentrated. Flash column chromatography (hexanes/EtOAc, 8:2) afforded the desired aldehyde 2.7 in almost quantitative yield (271 mg, 0.68 mmol).

Colorless oil; Rf 0.28 (hexanes/EtOAc 8:2); 1_{H NMR (400 MHz, CDCl3) δ 9.64}

(t, J = 3.0, 1H, H18), 5.70 (q, J = 0.4, 1H, H14), 2.62 – 2.59 (m, 1H, H17), 2.55 (m, 1H, H17’), 1.82 (s, 3H, Me15), 1.45 (s, 3H, Me16), 1.19 – 1.08 (m, 3H, Si(CH(CH3)2)3), 1.06 (d, J = 3.0, 18H, Si(CH(CH3)2)3), 0.97 (t, J = 8.0, 9H, Si(CH2CH3)3), 0.61 (q, J = 8.0, 6H, Si(CH2CH3)3).

(1E,3R)-2,3-Dimethyl-3-triethylsilyloxy-1-triisopropylsilyl-1,5-hexadiene 2.8

Cp2TiMe2 (2.80 mL, 2.10 mmol) was added to a solution of aldehyde 2.7 (289 mg, 0.70 mmol) in toluene (7.0 mL) and the reaction was heated at 70 °C overnight. It was then filtered through a Celite pad and washed with hexanes (3 mL). The solvent was removed under reduced pressure. Flash column chromatography (hexanes/EtOAc, 8:2) afforded 2.8 (235 mg, 85% yield).

Experimental Section

V Colorless oil; Rf 0.91 (hexanes/EtOAc, 8:2); []20

D – 4.9 (c 1.00, CHCl3) 1H NMR (400 MHz, CDCl3) δ 5.77 – 5.67 (m, 1H, H18), 5.46 (q, J = 0.6, 1H, H14), 4.99 – 4.95 (m, 1H, H19), 4.95 – 4.93 (m, 1H, H19’), 2.36 – 2.24 (m, 1H,

H17), 1.76 (d, J = 0.6, 3H, Me15), 1.36 (s, 3H, Me16), 1.17 – 1.11 (m, 3H, Si(CH(CH3)2)3), 1.04 (d,

J = 5.8, 18H, Si(CH(CH3)2)3), 0.96 (t, J = 8.0, 9H, Si(CH2CH3)3), 0.60 (q, J = 8.0, 6H, Si(CH2CH3)3); 13C NMR (100.6 MHz, CDCl3) δ 133.7, 118.8, 116.3, 27.6, 19.6, 18.9, 12.2, 6.7, 6.4; IR (neat) 2923, 2865, 1458, 1014, 905, 883, 741 cm-1_.

(±)-(3E)-4-Iodo-3-methyl-3-buten-2-ol 2.1385

A 2 M solution of trimethylaluminium in hexanes (4.30 mL, 8.55 mmol) was added to a stirred solution of Cp2ZrCl2 (417 mg, 1.42 mmol) in CH2Cl2 (8 mL) at –23 °C. After 30 min, H2O (51 µL, 2.8 mmol) was carefully added during 20 min. After 30 min, a solution of 3-butyn-2-ol (200 mg, 2.85 mmol) in CH2Cl2 (2 mL) was added via canula. The reaction mixture was stirred overnight at –23 °C before a solution of iodine (940 mg, 3.70 mmol) in THF (2 mL) was added dropwise. After 20 min, the mixture was allowed to warm to room temperature, water (8 mL) was slowly added and the phases were separated. The aqueous phase was extracted with Et2O (3 x 6 mL) and the combined organic extracts were dried over MgSO4, filtered and concentrated. Flash column chromatography (hexanes/EtOAc, 7:3) afforded 2.13 (263 mg, 43% yield).

Yellow oil; Rf 0.58 (hexanes/EtOAc, 7:3); 1_{H NMR (400 MHz, CDCl3) δ 6.31 (q, J = 1.0,}

1H, H14), 4.44 – 4.32 (m, 1H, H16), 1.84 (d, J = 1.0, 3H, Me15), 1.30 (d, J = 6.4, 3H,

Me16); 13_{C NMR (100.6 MHz, CDCl3) δ 151.3, 77.7, 72.6, 21.8, 20.0.}

(

3E)-4-Iodo-3-methylbut-3-en-2-one 2.12

Freshly distilled oxalyl chloride (1.50 mL, 17.7 mmol) was added dropwise to a stirred solution of DMSO (2.50 mL, 35.4 mmol) in CH2Cl2 (50 mL) at –78 °C. After 30 min a solution of alcohol 2.13 (2.50 g, 11.8 mmol) in CH2Cl2 (10 mL) was transferred via canula. After 30 min Et3N (8.20 mL, 59.0 mmol) was added dropwise and the reaction was stirred for 2 h at 0 °C. Then, it was diluted with Et2O (20 mL) and the organic extract was washed with saturated NaHCO3 solution (10 mL), dried over MgSO4, filtered and concentrated. Flash column chromatography (hexanes/EtOAc, 8:2) afforded the desired ketone 2.12 in 80% yield (1.98 g, 9.45 mmol).

VI

Yellowish oil; Rf 0.60 (hexanes/EtOAc, 8:2); 1_{H NMR (400 MHz, CDCl3) δ 7.78 (q, J =}

1.2, 1H, H14), 2.35 (s, 3H, Me16), 2.01 (d, J = 1.2, 3H, Me15).

B-Allyl-1,3,2-dioxaborinane 93

To an oven-dried 500 mL round-bottom flask charged with a magnetic stir bar and flushed with argon, was added trimethyl borate (10.4 g, 100 mmol) in Et2O (100 mL) and cooled to −78 °C. A solution of allylmagnesium bromide (1.0 M in Et2O, 14.5 g, 100 mmol) was added dropwise from an addition funnel over 30 min. The reaction was stirred for 2 h at −78 °C and allowed to warm to room temperature. The reaction was cooled to 0 °C, and 3 M HCl (120 mL) was added slowly through an addition funnel. The mixture was stirred until all solids were solved, the organic layer was separated and the aqueous layer was extracted with Et2O (3 x 50 mL). The organic layers were combined and dried over MgSO4, filtered, and concentrated to 200 mL in a dry 500 mL round-bottom flask. To the resultant solution 1,3-propanediol (7.2 mL, 100 mmol) and flame-dried 4-Å molecular sieves (20 g) were added. The suspension was allowed to stir at room temperature for 16 h. The reaction mixture was filtered through a sintered glass funnel and the molecular sieves were washed with Et2O (2 x 75 mL). The solvent was removed with a rotary evaporator without allowing the water bath to exceed 25 °C. The crude product was then solved in pentane (150 mL) to give a cloudy suspension and filtered through a pad of Celite®. The solvent was removed under reduced pressure and the resulting clear liquid was dissolved in pentane:Et2O 2:1 (100 mL) and loaded on a short, pre-equilibrated silica gel column and flushed with an additional 200 mL of solvent. The solution is concentrated in an oven-dried 500 mL round bottom flask, charged with a magnetic bar, placed in an ice bath and concentrated to constant weight under high vacuum with stirring, to yield B-allyl-1,3,2 dioxaborinane (11.4 g, 90% yield) as a colorless liquid. The spectral data was in agreement with reported values.197

1_{H NMR (400 MHz, CDCl3) δ 5.87 (ddt, J = 17.6, 10.0, 7.7, 1H), 4.98 – 4.91 (m,}

1H), 4.91 – 4.86 (m, 1H), 3.98 (t, J = 5.5, 4H), 2.01 – 1.87 (m, 2H), 1.60 (d, J = 7.3, 2H).

(1E,3S)-1-Iodo-2,3-dimethylhexa-1,5-dien-3-ol ent-1.1

A 5 mL round-bottom flask was charged with a stir bar and flushed with Ar. To the flask was added (S)-(–)-3,3’-dibromo-1,1’-bi-2-napthol (42 mg, 0.094 mmol), t-BuOH (692 mg,

Experimental Section

VII 9.36mmol) and B-allyl-1,3,2-dioxaborinane (883 mg, 7.02 mmol). The mixture was stirred at room temperature for 5 min and ketone 2.12 (983 mg, 4.68 mmol) was added dropwise. The reaction mixture was stirred at room temperature for 24 h, dissolved in hexanes and purified by flash chromatography (hexanes/EtOAc, 98:2) to afford the homoallylic alcohol ent-1.1 in 92% yield and 89% ee.

Colorless oil; Rf 0.35 (hexanes/EtOAc, 9:1); []20

D – 32.9 (c 1.00, CHCl3) for an

enantiomerically enriched sample with 89% ee. The enantiomeric ratio was determined by HPLC analysis using Chiralpak IA column (hexanes/i_{PrOH, 99:1),}

1.0 mL/min, 20 °C, 254 nm, τmajor = 8.44 min, τminor = 9.17 min); 1_{H NMR (400 MHz, CDCl3) δ 6.39}

(q, J = 1.0, 1H, H14), 5.66 (dddd, J = 16.9, 10.3, 8.4, 6.4, 1H, H18), 5.20 – 5.11 (m, 2H, H19), 2.51 (ddt, J = 13.9, 6.4, 1.2, 1H, H17), 2.26 (dd, J = 13.9, 8.4, 1H, H17’), 1.89 (d, J = 1.0, 3H, Me15), 1.34 (s, 3H, Me16); 13_{C NMR (100.6 MHz, CDCl3) δ 151.6, 133.0, 120.0, 78.2, 76.5, 45.2, 27.3,}

21.9.

(71E,3S)-1-Iodo-2,3-dimethyl-3-triethylsilyloxy-1,5-hexadiene ent-2.11

TESOTf (1.00 mL, 4.72 mmol) was added to a stirred solution of alcohol ent-1.1 (1.08 g, 4.29 mmol) and 2,6-lutidine (0.74 mL, 6.4 mmol) in CH2Cl2 (43 mL) at 0 °C. After 30 min, water (20 mL) was added and the aqueous phase was extracted with CH2Cl2 (3 x 10 mL). The combined organic layers were dried over MgSO4, filtered and concentrated. Flash column chromatography (hexanes) afforded ent-2.11 in quantitative yield.

Colorless oil; Rf 0.81 (hexanes/EtOAc, 98:2); []20

D +5.7 (c 1.00, CHCl3); 1H NMR (400 MHz, CDCl3) δ 6.27 (s, 1H, H14), 5.71 – 5.59 (m, 1H, H18), 5.05 – 4.94 (m, 2H, H19), 2.37 – 2.24 (m, 2H, H17), 1.84 (s, 3H, Me15), 1.38 (s, 3H, Me16), 0.94 (t, J = 7.9, 9H, Si(CH2CH3)3), 0.59 (q, J = 8.2, 6H, Si(CH2CH3)3); 13C NMR (100.6 MHz, CDCl3) δ 151.9, 134.2, 117.3, 79.3, 78.4, 46.7, 26.8, 21.7, 7.3, 6.8. (1E,3S)-3-(tert-Butyldimethylsilyloxy)-1-iodo-2,3-dimethyl-1,5-hexadiene 2.14

TBSOTf (0.55 mL, 2.4 mmol) was added to a stirred solution of alcohol ent-1.1 (505 mg, 2.00 mmol) and 2,6-lutidine (0.35 mL, 3.0 mmol) in CH2Cl2 (16 mL) at 0 °C. After 30 min, water (10 mL) was added and the aqueous phase was extracted with CH2Cl2 (3 x 10 mL). The combined

VIII

organic layers were dried over MgSO4, filtered and concentrated. Flash column chromatography (hexanes) afforded 2.14 in quantitative yield (730 mg).

Colorless oil; Rf 0.86 (hexanes/EtOAc, 96:4); 1_{H NMR (400 MHz, CDCl3) δ 6.29}

(q, J = 1.0, 1H, H14), 5.65 (ddt, J = 17.2, 10.4, 7.0, 1H, H18), 5.04 – 4.95 (m, 2H,

H19), 2.35 (dd, J = 14.2, 7.3, 1H, H107), 2.28 (dd, J = 14.2, 6.9, 1H, H17’), 1.84

(d, J = 1.0, 3H, Me15), 1.38 (s, 3H, Me16), 0.89 (s, 9H, SiC(CH3)3), 0.10 (s, 3H, SiCH3), 0.05 (s, 3H,

SiCH3); 13C NMR (100.6 MHz, CDCl3) δ 152.0, 134.2, 117.4, 79.4, 78.4, 46.5, 26.9, 26.1, 25.9, 21.8,

18.6, -1.8, -2.4.

(1E,3R)-1-Iodo-2,3-dimethyl-3,5-bis(trimethylsilyloxy)-1-pentene 2.9

Vinyl silane 2.6 (234 mg, 0.45 mmol) was dissolved in 1,1,1,3,3,3-hexafluoro-2-propanol (2 mL) and then cooled to 0 °C. Ag2CO3 (38 mg, 0.14 mmol) was then added and the flask was protected from light. N-iodosuccinimide (123 mg, 0.55 mmol) was added to the solution and after 20 min the reaction was quenched by addition of an aqueous saturated Na2S2O3 solution (1 mL), diluted with water (1 mL) and extracted with CH2Cl2 (3 x 5 mL). The combined organic phases were dried over MgSO4, filtered and concentrated under reduced pressure. Purification by flash column chromatography (hexanes/EtOAc, 97:3) afforded the desired product, 2.9 (198 mg. 91%).

Colorless oil; Rf 0.4 (hexanes/EtOAc, 97:3); 1_{H NMR (400 MHz, CDCl3) δ}

6.29 (q, J = 1.0, 1H, H14), 3.61 (ddd, J = 10.1, 9.5, 5.5, 1H, H18), 3.45 (ddd, 10.1, 9.6, 5.8, 1H, H18’), 1.91 (ddd, J = 13.6, 9.5, 5.8, 1H, H17), 1.83 (d, J = 1.0, 3H, Me15), 1.77 (ddd, J = 13.6, 9.5, 5.5, 1H, H17’), 1.39 (s, 3H, Me16), 0.95 (t, J = 7.9, 9H, Si(CH2CH3)3), 0.94 (t, J = 7.9, 9H, Si(CH2CH3)3), 0.60 (q, J = 7.9, 6H, Si(CH2CH3)3), 0.57 (q, J = 7.9,

6H, Si(CH2CH3)3).

(1E,3R)-5-Iodo-3,4-dimethyl-3-triethylsilyloxy-4-pentenal 2.10

Freshly distilled (COCl)2 (180 μL, 1.36 mmol) was added dropwise to a stirred solution of DMSO (190 μL, 2.73 mmol) in CH2Cl2 at −78 °C. After 10 min, vinylsilane 2.9 (218 mg, 0.45 mmol) in CH2Cl2 (5 mL) was transferred via cannula and the reaction was allowed to warm to −35 °C. After 45 min at this temperature it was cooled to −78 °C and Et3N (750 μL, 5.46 mmol) was added

Experimental Section

IX dropwise and the reaction was stirred for 2 h at room temperature. Then, it was diluted with Et2O (10 mL) and the organic extract was washed with saturated NaHCO3 solution (10 mL), dried over MgSO4, filtered and concentrated. Flash column chromatography (hexanes/EtOAc, 9:1) afforded the desired aldehyde 2.10 in almost quantitative yield (271 mg).

Colorless oil; Rf 0.48 (hexanes/EtOAc, 9:1); 1_{H NMR (400 MHz, CDCl3) δ 9.63}

(dd, J = 3.2, 2.7, 1H, H18), 6.51 (q, J = 1.0, 1H, H14), 2.63 (dd, J = 15.2, 2.7, 1H,

H17), 2.42 (dd, J = 15.2, 3.2, 1H, H17’), 1.90 (d, J = 1.0, 3H, Me15), 1.49 (s, 3H,

X

8.2 Fragment II

Methyl (2S)-2-(tetrahydro-2H-pyran-2-yloxy)propanoate 3.3

3,4-Dihydro-2H-pyrane (3.4 mL, 38 mmol) was added to a solution of methyl (S)-lactate (3.0 mL, 3.9 g, 31 mmol) in dichloromethane (15 mL). The mixture was cooled at 0 °C and camphorsulphonic acid (15 mg, 0.06 mmol) was added. After stirring for 1.5 h at this temperature the reaction mixture became pale purple. The volatile compounds were evaporated under reduced pressure and the crude was purified by flash column chromatography (hexanes/EtOAc, 7:3), to furnish 3.3 (5.9 g, 100% yield) as a mixture of diastereomers.

Colorless oil; Rf 0.54 (hexanes/EtOAc, 7:3); 1_{H NMR (400 MHz, CDCl3)}  _{4.72 –}

4.62 (m, 1H, THP), 4.44 (q, J = 7.0, 0.66H, H25), 4.22 (q, J = 6.8, 0.34H, H25), 3.95 – 3.89 (m, 1H, THP), 3.74 (s, 3H, CH3O), 3.56 – 3.43 (m, 1H, THP), 1.92 – 1.72 (m, 1H, THP), 1.72

– 1.59 (m, 5H, THP), 1.46 (d, J = 7.0, 3 x 0.66H, H26), 1.40 (d, J = 6.8, 3 x 0.34H, Me26); 13_{C NMR}

(100.6 MHz, CDCl3)  173.5, 98.2, 97.3, 72.2, 69.6, 62.3, 62.1, 51.7, 51.6, 30.3, 30.0, 25.1, 19.0, 18.9, 18.5, 17.9; IR (neat) 1741 cm-1_{; MS (ESI+) [M+Na]}+ _211.1.

(2S)-2-(Tetrahydro-2H-pyran-2-yloxy)propanal 3.4

DIBAL-H (1 M in hexanes, 10.7 mL, 10.7 mmol) was added dropwise to a solution of compound 3.3 (2.00 g, 10.7 mmol) in dichloromethane (21 mL) at −78 °C, and the resulting mixture was stirred for 1 h. A saturated aqueous solution of Rochelle’s salt was then added (20 mL) and the mixture was vigorously stirred for 2 h to obtain a clean phase separation. The aqueous phase was extracted with dichloromethane (3 x 25 mL) and the combined organic extracts were washed with brine (50 mL), dried over MgSO4 and evaporated under reduced pressure. Flash column chromatography of the residue (hexanes/EtOAc, 7:3) afforded the title compound as a mixture of diastereomers (1,42 g, 85% yield).

Colorless oil; Rf 0.4 (hexanes/EtOAc, 7:3); 1_{H NMR (400 MHz, CDCl3)}  _{9.66 – 9.64}

(m, 1H, CHO), 4.71 (dd, J = 4.4, 2.9, 0.66H, THP), 4.64 (dd, J = 5.4, 2.7, 0.34H, THP), 4.24 (qd, J = 7.1, 1.3, 0.66H, H25), 3.98 (qd, J = 6.9, 2.3, 0.34H, H25), 3.93 – 3.83 (m, 1H, THP),

Experimental Section

XI 3.56 – 3.41 (m, 1H, THP), 1.93 – 1.44 (m, 6H, THP), 1.35 (d, J = 7.1, 3 x 0.66H, Me26), 1.27 (d, J = 6.9, 3 x 0.34H, Me26);13_{C NMR (100.6 MHz, CDCl3)}  _{203.3, 203.0, 99.2, 98.1, 78.4, 76.3, 63.4,}

62.6, 30.5, 30.4, 25.3, 25.1, 19.8, 19.2, 15.6, 15.0; IR (neat) 1740 cm-1_{; MS (ESI+) [M+Na]}+ _181.1.

Bis(2,2,2,-trifluoroethyl) ethylphosphonate 3.6a96

Ethylphosphonic dichloride (5.00 g, 34.0 mmol) in THF (8 mL) was added dropwise with vigorous stirring to a mixture of trifluoroethanol (6.95 g, 69.7 mmol) and triethylamine (10 mL, 7.25 g, 68 mmol) in THF (60 mL). The solution was then stirred for 2 h at room temperature. The resulting triethylamine hydrochloride was filtered, washed with THF and the organic filtrate concentrated under reduced pressure. Product 3.6a (8.4 g, 90% yield) was used without further purification in the next step.

Brown oil; 1_{H NMR (400 MHz, CDCl3)}  _{4.45 – 4.32 (m, 4H, CF3CH}

2O), 1.94

(dq, J = 18.8, 7.7, 2H, CH3CH2), 1.23 (dt, J = 21.6, 7.7, 3H, CH3CH2).

Spectroscopic data are in agreement with those previously reported in the literature.96

Ethyl 2-(bis(2,2,2-trifluoroethoxy)phosphoryl)propanoate 3.696

HMDS (16.7 mL, 80.1 mmol) in THF (53 mL) was added dropwise to a stirred solution of

n-BuLi in hexanes (1.6 M, 45.7 mL, 73.1 mmol) at −20 °C. After 15 min, the mixture was cooled

to −78 °C, and phosphonate 3.6a (9.55 g, 34.8 mmol) and ethyl chloroformate (3.4 mL, 3.86 g, 36 mmol) in THF (120 mL) were added via cannula simultaneously. The solution was allowed to warm to 0 °C over 30 min. It was then treated with aqueous HCl until the pH of the mixture was acid. Then the aqueous phase was extracted with dichloromethane (3 x 30 mL) and the combined organic layers dried with MgSO4 and concentrated under reduced pressure, obtaining product 3.6(9.0 g, 74% yield).

Brown oil; 1_{H NMR (400 MHz, CDCl3)}  _{4.41 – 4.34 (m, 4H, CF3CH} 2O),

4.17 (q, J = 7.1, 2H, CH3CH2O), 3.12 (dq, J = 22.4, 7.4, 1H, CH3CH), 1.45

(dd, J = 19.4, 7.4, 3H, CH3CH), 1.23 (t, J = 7.1, 3H, CH3CH2O).

XII

Ethyl (2Z,4S)-2-methyl-4-(tetrahydro-2H-pyran-2-yloxy)-2-pentenoate 3.5

A solution of KHMDS (0.5 M in toluene, 26.8 mL, 13.4 mmol) was added dropwise to a stirred solution of phosphonate 3.6 (4.63 g, 13.4 mmol) and 18-crown-6 (8.17 g, 30.9 mmol) in THF (30 mL) at −78 °C. The solution was left to warm to room temperature for 15 min and then cooled again to −78 °C. A solution of aldehyde 3.4 (1.62 g, 10.30 mmol) in THF (4 mL) was added dropwise and the mixture was stirred for 45 min. The reaction was then warmed to room temperature over 2 h and quenched by addition of a saturated NH4Cl aqueous solution. The layers were separated, the organic layer was washed with H2O (3 x 20 mL) and the aqueous layers extracted with Et2O (3 x 10 mL). The organic layers were combined and washed with a saturated aqueous NaHCO3 solution (40 mL), dried with MgSO4, filtered and concentrated under reduced pressure. The residue was purified by flash column chromatography (hexanes/EtOAc 6:4) to give Z olefin 3.5 (2.45 g, 82% yield).

Colorless oil; Rf 0.6 (hexanes/EtOAc, 7:3); 1_{H NMR (400 MHz, CDCl3) δ 6.04}

(dq, J = 8.0, 1.4, 0.5H, H24), 5.79 (dq, J = 8.5, 1.4, 0.5H, H24), 5.14 – 5.03 (m, 1H, H25), 4.65 (t, J = 3.8, 0.5H, THP), 4.54 (t, J = 3.9, 0.5H, THP), 4.23 – 4.16 (m, 2H, CH3CH2O),

3.92 – 3.81 (m, 1H, THP), 3.51 – 3.41 (m, 1H, THP), 1.92 (d, J = 1.4, 3x0.5H, Me23), 1.91 (d, J = 1.2, 3x0.5H, Me23), 1.60 – 1.46 (m, 6H, THP), 1.33 – 1.27 (m, 6H, Me26 + CH3CH2O); 13C NMR

(100.6 MHz, CDCl3) δ 164.2, 163.6, 146.6, 144.7, 98.9, 97.9, 72.0, 70.0, 64.2, 64.0, 61.7, 61.5, 32.3, 32.3, 26.7, 26.6, 21.6, 21.5, 21.3, 21.2, 21.1, 15.4.

(S)-3,5-Dimethylfuran-2(5H)-one 3.199

30% (v/v) sulfuric acid (0.1 mL, 20% mmol) was added to a solution of alkene 3.5 (1.31 g, 5.41 mmol) in MeOH (55 mL). The reaction mixture was stirred for 2 h, quenched with a saturated aqueous NaHCO3 solution and extracted with dichloromethane (3 x 10 mL). The organic layer was dried with MgSO4, filtered and evaporated at 300 mmHg and 38 °C. The residue was purified by flash column chromatography (hexanes/EtOAc, 7:3) to obtain 3.1 (556 mg, 91%).

Experimental Section

XIII Colorless oil; Rf 0.6 (CH2Cl2/MeOH, 98:2); []20

D +89.6 (c 1.00, CHCl3) [lit.99 +91.5 (c

1.24, CHCl3)]; 1_{H NMR (400 MHz, CDCl3)}  _{7.04 – 6.99 (m, 1H, H24), 5.03 – 4.94 (m,}

1H, H25), 1.92 (t, J = 1.7, 3H, Me26), 1.41 (d, J = 6.8, 3H, Me23); 13_{C NMR (100.6 MHz,}

CDCl3) δ 174.4, 149.9, 129.8, 77.2, 19.2, 10.7; IR (neat) 3000, 2950, 1770, 1670, 1460, 1340, 1210, 1100, 1090, 1030, 1000, 950, 860, 760 cm-1_{; HRMS (ESI+) calcd for C6H9O2}+ _[M+H]+

113.0597, found 113.0597.

(3R,5S)-3,5-Dimethyldihydrofuran-2(3H)-one 3.2102

Rhodium on alumina (384 mg, 0.19 mmol) was added to a stirred solution of lactone 3.1 (209 mg, 1.86 mmol) in ethyl acetate (3.7 mL) under a nitrogen atmosphere. The suspension was stirred under a hydrogen atmosphere for 6 h. The mixture was then filtered through Celite, washed with ethyl acetate and concentrated at 300 mmHg to obtain product 3.2 (175 mg, 82%) as a colorless oil, which was used without further purification in the next step.

Colorless oil; Rf 0.67 (CH2Cl2/MeOH, 8:2); []20

D −2.8 (c 1.00, CHCl3) [lit.102 −4.6 (c

1.00, CHCl3)]; 1_{H NMR (400 MHz, CDCl3)}  _{4.49 – 4.40 (m, 1H, H25), 2.71 – 2.59 (m,}

1H, H23), 2.49 (ddd, J = 12.5, 8.5, 5.4, 1H, H24), 1.46 (td, J = 12.3, 10.4, 1H, H24’), 1.39 (d, J = 6.4, 3H, Me26), 1.24 (d, J = 7.0, 3H, Me23); 13_{C NMR (100.6 MHz, CDCl3) δ 180.7, 76.1,}

40.3, 37.5, 22.1, 16.3; IR (neat) 1765, 1460, 1390, 1350, 1180, 1050, 955 cm-1_{; HRMS (ESI+) calcd} for C6H11O2+ _[M+H]+ _{115.0754, found 115.0769.}

(3R,5S)-3,5-Dimethyltetrahydrofuran-2-ol 1.9

DIBAL-H (1 M in hexane, 14.0 mL, 14.0 mmol) was added dropwise to a solution of compound 3.2 (1.45 g, 12.7 mmol) in dichloromethane (120 mL) at −78 °C and the resulting mixture was stirred for 15 min at this temperature. A saturated aqueous solution of Rochelle’s salt was then added (50 mL) and the mixture was vigorously stirred for 2 h to obtain a clean phase separation. The aqueous phase was extracted with dichloromethane (3 x 20 mL) and the combined organic extracts were washed with brine (50 mL), dried over MgSO4 and evaporated under reduced pressure. Flash column chromatography of the residue (hexanes/EtOAc, 7:3) gave compound 1.9 (1.32 g, 90%).

XIV

Colorless oil; Rf 0.5 (CH2Cl2/MeOH, 8:2); 1_{H NMR (400 MHz, CDCl3)}  _{5.20 (d, J = 7.0,}

0.37H, H22), 5.10 (d, J = 3.5, 0.63H, H22), 4.33 (dp, J = 9.2, 6.1, 0.63H, H25), 4.13 (dp, J = 10.0, 6.1, 0.37H, H25), 3.16 (brs, 1H, OH), 2.85 (brs, 1H, OH), 2.30 – 2.12 (m, 1.63H, H23+H24), 2.09 – 2.00 (m, 0.37H, H24), 1.47 – 1.34 (m, 0.37H, H24’), 1.32 (d, J = 3.1, 3x0.37H, Me26), 1.25 (d, J = 6.1, 0.63x3H, Me26), 1.13 – 1.10 (m, 0.63H, H24’) 1.10 (d, J = 7.0, 3x0.37H, Me23), 1.09 (d, J = 7.0, 3x0.63H, Me23); 13_{C NMR (100.6 MHz, CDCl3) δ 104.88, 99.48,} 76.47, 74.79, 42.12, 41.20, 39.98, 38.84, 23.31, 21.35, 18.24, 12.92; IR (neat) 3388, 2964, 1079, 1000 cm-1_{; HRMS (ESI+) calcd for C6H12NaO2}+ _[M+Na]+ _{139.0730, found 139.0743.}

General procedure for the Horner–Wadsworth–Emmons reaction

The base (see Tabla 3.1) was added to a solution of the desired phosphonate in the indicated solvent. After stirring for 30 minutes, this mixture was added dropwise to a solution of lactol 1.9 (30 mg, 0.26 mmol) in the solvent (3.7 mL) indicated in the table at the temperature shown, and the mixture was stirred for 16 h. A saturated aqueous ammonium chloride solution was added (2 mL), and the aqueous phase was extracted with dichloromethane (3 x 3 mL). The combined organic phases were dried with MgSO4 and evaporated under reduced pressure. Flash column chromatography of the residue (CH2Cl2/MeOH, 96:4) afforded the desired product.

General procedure for the Wittig reaction

The phosphonium ylide (see Tabla 3.2) (1.3 mmol) was added to a solution of lactol 2.8 (116 mg, 1 mmol) in toluene (6.25 mL) and trifluoroethanol (2.0 mmol) when applicable (see

Tabla 3.2). The reaction mixture was warmed to the temperature shown for 16 h. The mixture

was then concentrated under reduced pressure and purified by flash column chromatography (CH2Cl2/MeOH, 96:4) to obtain the desired alkene.

Ethyl 2-((2S,3R,5S)-3,5-dimethyltetrahydrofuran-2-yl)acetate 3.8a

Colorless oil; Rf 0.35 (CH2Cl2/MeOH, 98:2); 1_{H NMR (400 MHz, CDCl3)}  _{4.15 (q,} J = 7.2, 2H, CH3CH2O), 4.11 – 4.05 (m, 1H, H25), 3.90 (td, J = 7.5, 5.5, 1H, H22),

2.51 – 2.46 (m, 2H, H21), 2.22 – 2.13 (m, 1H, H24), 2.02 – 1.94 (m, 1H, H23), 1.26 (t, J = 7.1, 3H CH3CH2O), 1.22 (d, J = 6.1, 3H, Me26), 1.21 – 1.15 (m, 1H, H24’), 1.04 (d, J = 6.6, 3H, Me23); 13_{C NMR (100.6 MHz, CDCl3) 171.7, 81.4, 74.7,}

Experimental Section

XV

2-((2S,3R,5S)-3,5-Dimethyltetrahydrofuran-2-yl)-1-(morpholinyl)ethanone 3.8b

Colorless oil; Rf 0.24 (CH2Cl2/MeOH, 96:4); 1_{H NMR (400 MHz, CDCl3)}  _4.09

– 4.01 (m, 1H, H25), 3.96 – 3.86 (m, 1H, H22), 3.72 – 3.47 (m, 8H, OCH2CH2N), 2.61 – 2.47 (m, 2H, H21), 2.22 – 2.10 (m, 1H, H24), 2.09 – 1.97 (m, 1H, H23), 1.28 – 1.23 (m, 1H, H24’), 1.21 (d, J = 6.0, 3H, Me26), 1.06 (d, J = 6.5, 3H, Me23); 13_{C NMR (100.6 MHz, CDCl3) 169.8, 82.1, 74.8, 67.0, 46.8,} 43.3, 42.1, 40.6, 38.2, 21.7, 17.0; MS (ESI+) [M+H]+ _228.2. Methyl 2-((2S,3R,5S)-3,5-dimethyltetrahydrofuran-2-yl)acetate 3.8c

Colorless oil; Rf 0.38 (CH2Cl2/MeOH, 96:4); 1_{H NMR (400 MHz, CDCl3)}  _{4.16 –}

4.03 (m, 1H, H25), 3.96 – 3.86 (m, 1H, H22), 3.69 (s, 3H, CH3O), 2.54 – 2.47 (m,

2H, H21), 2.22 – 2.13 (m, 1H, H24), 2.04 – 1.94 (m, 1H, H23), 1.22 (d, J = 6.1, 3H, Me26), 1.20 – 1.15 (m, 1H, H24’), 1.04 (d, J = 6.6, 3H, Me23).

Ethyl (2E,4R,6S)-6-hydroxy-4-methyl-2-heptenoate 1.8a

Colorless oil; []20 D = −19.2 (c 1.10, CHCl3); 1H NMR (400 MHz, CDCl3)  6.90 (dd, J = 15.7, 7.8, 1H, H22), 5.80 (dd, J = 15.7, 1.2, 1H, H21), 4.18 (q, J = 7.1, 2H, CH3CH2O), 3.90 – 3.82 (m, 1H, H25), 2.56 - 2.47 (m, 1H, H23), 1.44 – 1.36 (m, 1H, H24), 1.34 – 1.25 (m, 1H, H24’), 1.29 (t, J = 7.1, 3H, CH3CH2O), 1.20 (d, J = 6.1, 3H, Me26), 1.09 (d, J = 6.7, 3H, Me23); 13_{C NMR (100.6 MHz, CDCl3)}  167.0, 154.4, 119.7, 65.8, 60.4, 45.4, 33.6, 24.0, 19.3, 14.4; IR (neat) 3500, 3000, 1730, 1660, 1380, 1300, 1190, 1140 cm-1_. (2E,4R,6S)-6-Hydroxy-4-methyl-1-(4-morpholinyl)-2-hepten-1-one 1.8b Colorless oil; 1_{H NMR (400 MHz, CDCl3)}  _{6.84 (dd, J = 15.1, 7.7, 1H, H22),} 6.18 (dd, J = 15.1, 1.1, 1H, H21), 3.92 – 3.82 (m, 1H, H25), 3.72 – 3.42 (m, 8H, OCH2CH2N), 2.58 – 2,46 (m, 1H, H23), 1.64 – 1.54 (m, 1H, H24), 1.45 – 1.37 (m, 1H, H24’), 1.21 (d, J = 6.1, 3H, Me26), 1.09 (d, J = 6.7, 3H, Me23); 13_{C NMR (100.6 MHz, CDCl3)}  _{165.7, 152.3, 117.3, 66.6, 65.3,} 46.0, 45.4, 42.1, 33.6, 23.8, 19.3.

XVI Methyl (2E,4R,6S)-6-hydroxy-4-methyl-2-heptenoate 1.8c Colorless oil; 1_{H NMR (400 MHz, CDCl3)}  _{6.90 (dd, J = 15.7, 7.8, 1H, H22),} 5.78 (dd, J = 15.7, 1.1, 1H, H21), 3.89 – 3.76 (m, 1H, H25), 3.71 (s, 3H, OMe), 2.59 – 2.42 (m, 1H, H23), 1.62 – 1.53 (m, 1H, H24), 1.42 – 1.30 (m, 1H, H24’), 1.18 (d, J = 6.1, 3H, Me26), 1.06 (d, J = 6.7, 3H, Me23); 13_{C NMR (100.6 MHz,} CDCl3)  167.4, 154.7, 119.3, 65.9, 51.6, 45.4, 33.6, 24.1, 19.3. (2E,4R,6S)-6-Hydroxy-N-methoxy-N,4-dimethyl-2-heptenamide 1.8d Colorless oil; 1_{H NMR (400 MHz, CDCl3)  6.88 (dd, J = 15.5, 8.0, 1H, H22),} 6.36 (dd, J = 15.5, 1.0, 1H, H21), 3.90 – 3.77 (m, 1H, H25), 3.67 (s, 3H, CH3ON), 3.21 (s, 3H, CH3N), 2.62 – 2.44 (m, 1H, H23), 1.61 (ddd, J = 13.8, 8.0, 6.7, 1H, H24), 1.39 (ddd, J = 13.7, 7.7, 5.1, 1H H24’), 1.17 (dd, J = 5.9, 4.3, 3H, Me26), 1.07 (d, J = 6.7, 3H, Me23). Methyl (2R,3S,4R,6S)-2,3,6-trihydroxy-4-methylheptanoate 3.11C

AD-mix- (4.20 g) was added to a stirred solution of alkene 1.8C (172 mg, 1.00 mmol) in a mixture of t_{BuOH:H2O (1:1) (10 mL) at 0 °C. After the addition of methanesulfonamide (285}

mg, 3.00 mmol) the mixture was stirred at 0 °C overnight. The reaction was then quenched with Na2S2O3·5H2O (1.38 g, 5.54 mmol) and stirred for 45 min at room temperature. The layers were

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