CAPÍTULO 2 TENDENCIAS Y TECNOLOGÍAS ACTUALES A DESARROLLAR
2.11 L ENGUAJES DE PROGRAMACIÓN
A further study into this reaction proved that other Michael acceptors including 2-benzylidenemalonates and 2-benzylidenemalononitriles could be successfully utilised (Scheme 1.34).170 SAMP-hydrazones (S)-117 is transformed to the 2-substituted 4-oxo-diesters and dinitriles (R)-127 after oxidative cleavage of the 1,4-adducts by ozonolysis in good overall yields of 50-82% and high enantioselectivities.
Numerous other Michael acceptors are tolerated under the reaction conditions.171-173,31 The reaction has also been successful with cyclic SAMP/RAMP-hydrazones, with resultant ketones being obtained in high yields and selectivities.174-176 A recent publication by Sammet et al.177 provides an insight into the use of both acyclic and cyclic SAMP/RAMP-hydrazones as a traceless auxiliary in the asymmetric 1,4-addition of cuprates to enones.177
45
R1 N N
O
(S)-117
R1 X
O 1. LDA
2.
3. O3
R1= Me, Et, Ph
R2= H, 3-OMe, 4-OBn, 4-OMe X = CO2CH3, CN
X R2 X
R2 X
(R)-127 50-82%
ee = >95%
Scheme 1.34 Asymmetric Michael additions using 2-benzylidenemalonates and 2-benzylidenemalononitriles as acceptors.
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