0 、±RCH2 CCHCOOC2H5+CHO R 0 RCH2C-ccooc2H5←→ RCH2C=CCOOC2Hs]C2H5OH ORH旷 R 0 RCH2CCHCOOC2H5 O CH3 2 CH3CH2CHCOOC2Hs 1)(C6Hs)3CNa CH:CH2CH-C-C-COOC2Hs CH3 2)H CH3 CH2CH3