●○ COOC2Hs COOC2Hs COOC2Hs COOC2Hs COOC2H5 COOH CO2R-CH2COOH COOH OOCCRCHsHRCOOH R-CH ②RX R COOCH R COOHCH2 COOC2H5 COOC2H5 C2H5ONa CH COOC2H5 COOC2H5 [ ] -Na + RX CH COOC2H5 COOC2H5 R H+ H2O CH COOH COOH R -CO2 Δ R CH2COOH ① R' COOH COOH C R R' COOC2H5 COOC2H5 C R R CHCOOH R' -CO2 Δ R'X CH COOC2H5 COOC2H5 R C2H5ONa ② H2O,H+