Phosphorylation of salicylaldiimines with chiral alkylene chlorophosphites

Abstract

The reaction of diimine Ia with chlorophosphite II proceeds readily in the methylene chloride medium to afford salt IVa as a mixture of two diastereomers, as follows from the P NMR spectrum of the reaction mixture, which contains two singlet peaks at –114.41 and –115.04 ppm in a 1:1 ratio. Compound IVa contains three chiral centers but is formed only as a mixture of two diastereomers, indicating that the process of cascade cyclization occurs with a high stereoselectivity. Salt IVa loses hydrogen chloride molecule under treating with triethylamine turning into neutral product Va (δР –102.42, –102.85 ppm). In view of the data, we introduced optically pure diimine Ib into the reaction with 2-chloro-4,5-dimethyl-1,3,2-dioxaphospholane III to isolate phosphorus-containing framework structures in optically pure form.