OH CH OH COEt COOT CH H 13--氧 +CH,o Etooc n comet 0=CH OH OHC CHO CH2(CO, Et)2 KCO 2OH NH CHO CHOCO2 Et OH CH OH CH COOEt 2+ 2- C H H EtOOC COOEt O CH OH 1,3__ _ 氧 OHC +CH2 O O O CHO CH2 O K3 CO3 CHO OH CH2 (CO2 Et) 2 NH3 O O