Sincronización sin relé de sincronismo

A further series of compounds was synthesi sed that i ncluded a polyether chain i n place of the crown ether. The anticipated advantage of thi s system was that cations would be complexed less strongly, therefore releasing more easily, an attri bute that would be i mportant in a real -ti me sen s i n g appl i cation. Compounds of the type depicted i n Fig. 2. 1 8 were targeted.

Figure 2.1 8 Open -chain polyether styryl-substituted terthiophenes targeted

It was envisaged that these compounds could be synthesised from a reaction between terthiophene phosphonate and a s ubstituted benzaldehyde in the same way that the crown-substituted terthiophenes were formed, as shown in Fig. 2. 1 9.

R, R2

+ KOtBu

Figure 2.1 9 Formation of open-chain ether fu nctional ised terthiophenes

The fi rst step toward maki ng these products was the formati on of the polyether­ substi tuted benzaldehydes. These could clearly be made by the reaction of an appropriate tosy lated ol i go(ethy leneglycol ) monomethyl ether together with either isovan i l l i n or vanillin, i n a Williamson ether synthesis reaction. A paper by Lauter, Meyer and Wegne�24 detai l s the synthesi s of these tosylated polyethers from thei r glycol counterparts. Whi le both diethylene glycol and triethylene glycol monomethyl ethers are commercially avai lable, any longer chain ethers m ust themse l ves be sy nthesi sed. The same paper by Lauter et al. descri bes the formation of tetra(ethylenegl ycol ) monomethyl ether from a W i l l iamson-ty pe etherification reaction between tri (ethyl eneglycol ) monomethyl ether and ethylene glycol. m These reactions are summarized in Scheme 1 0.

HO�O�O/ HO Na pTsCI NaOH 85% TSO�O�O/ pTsCI TSO�O�O�O/ 84% pTsCI NaOH TSO�O�O�O�O/ 81%

Once these starting material s had been synthesi sed, the reactions w ith vani l l i n and i sovan i l l i n u nder W i l l i amson conditions were strai ghtforward, Purification by col umn chromatog raphy l ed to the poly ether-substituted benzaldehyde products

XVII-XXII ( Scheme 1 1 ) in 50-80% yield, All of the products were i solated as fai ntly coloured l iquids and characterised by N M R and UV /VI S spectroscopy, and h i gh-resol ution mass spectrometry, A typical I H N M R spectrum exhibited, i n addi tion to an aldehyde peak at b 9.8, three sets of signal s due to aromatic protons i n the region b 6.9-7.5. Di stinct 3J and 4) coupl ing al lowed these to be uneq u ivocalI y assigned, The use of a long-range COSY spectrum assisted i n the assignment of the alkoxy signals (b 3 . 3 -4. 3), while HMQC and HMBC experiments pro v ided the remaining connectivity i nformation necessary to completely assign the 13C spectrum .

Scheme 1 1 n

o

n = 1 72% XVII n = 2 56% XVIII n = 3 49% XVIV n = 1 83% XX n = 2 55% XXI n = 3 54% XXII

Formation of polyether-su bstituted benzaldehydes XVI I­ XXII

A seri es of Horner-Emmons reactions between XVII-XXII and terthi ophene phosphonate were carried out (Scheme 1 2) , uti l izing the same conditions e mployed for the synthesi s of styry l - 1 5 -crown-5 terthiophene I. Allow i ng the reaction to proceed for 30-60 minutes at room temperature, fol Iowed by solvent extraction and sil ica-gel chromatography yielded the products XXIII-XXVIII in excel Ient 8 8-94% yields.

n = 1 XVII n = 2 XVIII n = 3 XVIV n = 1 88% XXIII n =

2

88% XXIV n = 3 93% XXV n = 1 XX n = 2 XXI n = 3 XXII n = 1 9 1 % XXVI n = 2 93% XXVII n = 3 94% XXVIII

Scheme 1 2 Horner-Emmons reaction to form open-chain terthiophenes

The I H NMR spectra of these compounds were very s i m i l ar to that of styryl- 1 5- cro w n -5 terthiophene I. The spectra obtai ned for the three i sovan i l l i n-deri ved compounds were i dentical i n the aromatic region Cb 6.8-7.5), as were the spectra for the three vanillin-deri ved compounds, only differing as expected i n the ether region (b 3. 3 -4.3, Fi g. 2.20) due to the differi ng lengths of the polyether chain attached. The slight differences in chemical shift i n the aromatic region between the i sovan i l l i n­ deri ved compounds XXIII-XXV and their vanillin-deri ved analogues XXVI-XXVII are i l l ustrated in Fig. 2.2 1 . IJC NMR and 2 0 NMR experiments (COSY, LR-COSY , H MQC and HMBC) al lowed the spectra for al l of the products to be completely assi gned. The DV!VIS spectra of these compounds were v i rtually identical to that

provided further evi dence for the formati on of the desi red o pen-chai n ether t e r t h i o p h e n e s X X I I I - X X V I I I . A fracti o n c o n ta i n i n g 1 ,2 - bis( l 2' , 2" ;5",2'' ' jterthiophen-3''-yl)ethene (3- 1 5 %) was also i solated from each of the reactions in Scheme 1 2, as descri bed earlier during the formation of styry l - 1 5-crown- 5 terthiophene I and styryl- 1 8-crown-6 terthiophene 11 ( Section 2.2.4)

The structures shown in Scheme 1 2 can be considered as open-chain equi valents of 1 2-crown-4, 1 5-crown-5 and 1 8-crown-6 when n = 1 , 2 or 3 respectively.

XXIII 4 . 2 XXIV 4 . 2 XXV 4 . 2 4 . 1 4 . 1 4 . 1 4 . 0 4 . 0 4 . 0 3 . 9 3 . 9 3 . 9 3 . 5 3 . 4 3 . 4 3 . 4

Figure 2.20 1H N M R spectra of open-chain terthiophenes XXIII-XXV (ether region)

ppm

ppm

7 . 4 7 . 3 7 . 2

7 . 4 7 . 3 7 . 2 7 . 1 7 . 0

ppm

i

6 . 9 ppm

Figure 2.21 Comparison of aromatic regions in 1 H N MR spectra of compounds XXIII and XXVI

An analogous styry l-terthiophene compound that didn 't contain a polyether chain (XXVIV) was synthesi sed as a reference (Scheme 1 3) . The cation complexing abil i ty of thi s monomer was expected to be neg l i gi ble when compared to the crown and open-chai n compounds. It was prepared from a Horner-Emmons reaction between terthi ophene phosphonate and 3,4-dimethoxybenzaldehyde in the same way as for the longer chain compounds. ' H NMR analysi s of the product after purification by si l ica gel chromatography showed it to consist exclusi vely of the trans i somer. \3C NMR gave the expected number of signals, which, along w ith the ' H NMR signals, could be

The UV IVIS spectrum was i dentical to that of the other polyether- and crown­ s ubstituted terthi ophenes, w ith Ama> = 329 nm. Samples analysed by h i gh-resol ution

mass spectrometry and elemental anal y s i s verified the successful synthe s i s of monomer XXVIV.

KO'Su +

XXVIV (86%) Scheme 1 3 Synthesis of d imeth oxystyryl terth iophene

A further two reference compounds, that had been previously synthesised i n our laboratories, were i ncl uded in spectroscopic (Chapter 4) and polymeri sation (Chapter

5) studies. m The structures of these compounds are i l l ustrated below (Fig. 2.22).

LXXVI LXXVII

F igure 2.22 Styryl terthiophene reference compounds

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