An Efficient Synthesis of Dialkyl 2-(Diphenoxyphosphoryl)-3-(alkylthio)succinates from Alkylthiols, Triphenyl Phosphite and Dialkyl Acetylenedicarboxylates

An efficient synthesis of dialkyl 2-(diphenoxyphosphoryl)-3-(alkylthio)succinates, as a mixture of two diastereomers, in 78- 90% yields, is described via reaction between alkylthiols, dialkyl acetylenedicarboxylates, and triphenyl phosphite. The structures of products were deduced from their high-field 1H, 13C, and 31P NMR spectra, and IR spectral data. Since these hosphonate esters possess two stereogenic centers, two diastereomers with gauche HCCH arrangements are possible. Observation of 3JHH = 3.5-4.6 Hz for the vicinal methine protons confirmed the dominance of the gauche arrangement. A mechanism is proposed for the formation of products