Differences in the crystal structures of two dialkyl diester triphenyl-phosphonium ylids

Abstract

Hydrogen bonding and crystal packing play major roles in determining the conformations of ethyl methyl 2-(triphenyl-phosphoranylidene)malonate, Ph3P=C(C02CH3)CO2CH2CH3 or C24H23O4P,(I), and dimethyl 2-(triphenylphosphoranylidene)malonate, Ph3P=C(CO2CH3)2 or C23H21O4P,(II). In (I), the acyl O atom of the ethyl ester group is anti to the P atom, while the O atom of the methyl ester group is syn. In (II), the dimethyl diester is a 1:1 mixture of anti-anti and synanti conformers.