SYNTHESE STEREOSELECTIVE D'ESTERS α,β-ETHYLENIQUES α-METHYLES Z OU E PAR LA REACTION DE WITTIG-HORNER A PARTIR DE PHOSPHONATES OU D'OXYDES DE PHOSPHINE

Article abstract of DOI:10.1016/S0040-4020(01)91264-5

The reaction of α-branched aldehydes with diethyl 1-carbomethoxyethyl phosphonate 1b in THF/nBuLi at low temperature leads stereoselectively to Z α-methyl α,β-unsaturated esters.From a linear aldehyde, the reaction is less stereoselective, while from α,β-unsaturated ones, the E isomers are predominantly formed in good yields.From diphenyl 1-carbomethoxyethyl phosphine oxide 2b, E α-methyl α,β-unsaturated esters are stereoselectively formed either in DMF/tBuOK or in phase transfer conditions, whatever the starting aldehyde is, also in good yields.This reagent can thus advantageously replace the corresponding P-ylid.In all cases, the reaction conditions are determined so that by-products formation is minimized.