COOCH3 ph CH2CH2COOCH3 CH3ONa ph CH3OOC CH2CHCOOCH; CH3O0C 环化方向含两种不同c-H时，酸性较大的-H优先被碱夺去。 COOC2H5 CH2CH2CH2COOC2Hs CH2CH2CHCOOC2H5 B CH>CHCOOC2H5 CH2CHCOOCH5 CH3 CH3 CH3 COOC2H5 CH2CH2CH2COOC2Hs CHCHCOOC2H5 CH3 CHs b -0 COOC2H5 H3C[环化方向] 含两种不同-H时, 酸性较大的-H优先被碱夺去。 C ph CH2CH2COOCH3 CH3OOC CH2CH2COOCH3 CH3ONa ph CH3OOC COOCH3 O CH2CH2CH2COOC2H5 CH2CHCOOC2H5 CH3 :B - CH2CH2CHCOOC2H5 CH2CHCOOC2H5 CH3 - COOC2H5 CH3 O CH2CH2CH2COOC2H5 CH2CHCOOC2H5 CH3 a b COOC2H5 O - CH3 O - H3C COOC2H5 a b