Asymmetric and Doubly Asymmetric 1,3-Dipolar Cycloadditons in the Synthesis of Enantiopure Organophosphorus Compounds

Abstract

Enantiopure five-membered ring nitrones derived from L-tartaric acid and from L-malic acid undergo highly regio- and stereoselective cycloaddition reactions with an excess of racemic 2,3-dihydro-l-phenyl-1H-phospholes producing two readily separable tricyclic cycloadducts and concomitantly effecting kinetic resolution of the dihydrophosphole derivative. Stereochemistry of the cycloaddition process and scope of the kinetic resolution process have been established in details and adjusted to produce dihydrophosphole derivatives in good yields and in very high optical purity. To effect syntheses of single cycloadducts of 100% ee the techniques of doubly asymmetric synthesis and parallel kinetic resolutions have been employed. The resulting tricyclic cycloadducts feature 2,2'-connection of pyrrolidine and phospholane rings and five to seven contiguous stereogenic centers of which three have been induced and one or two kinetically resolved during the cycloaddition process.