COOCH3 ph CH2CH2COOCH3 CH3ONa Ph =0 CH300C CH2CH2COOCH3 CH3O0C 环化方向]含两种不同-H时，酸性较大的c-H优先被碱夺去。 COOC2Hs CH2CH2CH2COOC2Hs CH2CH2CHCOOC2H5 :B CH2CHCOOC2Hs CH2CHCOOC2Hs =0 CH3 CH3 CH: COOC2Hs CH2CH2CH2COOC2Hs a 0 a CH2CHCOOC2Hs CH3 b CHa b 0 CoOC2Hs H3C