Highly diastereoselective[3+2] cycloadditions between nonracemic p-tolysulfinimines and iminoesters: an efficient entry to enantiopure imidazolidines and vicinal diaminoalcohols

A new procedure for the asymmetric synthesis of imidazolidines and vicinal diamines is reported. The 1,3-dipolar cycloaddition between nonracemic p-tolylsulfinimines and azomethine ylides generated in situ from alpha-iminoesters and LDA produces N-sulfinylimidazolidines with a high degree of stereocontrol. In contrast, the presence of Lewis acids promotes formation of the cycloadducts through a highly diastereoselective process with opposite stereochemistry. Subsequent transformations of the imidazolidines including oxidative, reductive, and hydrolytic processes that provide easy access to vicinal diaminoalcohols have been explored. Among these, reductive cleavage of the aminal with LiAlH4 is an extremely efficient and general reaction for the synthesis of enantiopure N-sulfinyl-N'-benzyldiaminoalcohols