ChemInform Abstract: Construction of Vicinal Quaternary Stereogenic Centers by Enantioselective Direct Mannich‐Type Reaction Using a Chiral Bis(guanidino)iminophosphorane Catalyst.

Abstract

Anovel asymmetric direct Mannich-type reaction of a-iminophenylacetate esters with thionolactones,bearing asubstituent at the a-position, as al ess acidic pronucleophile was developed. Using bis(guanidino)iminophosphorane as the chiral organosuperbase catalyst, the reaction afforded densely functionalizeda mino-acid derivatives having vicinal quaternary stereogenic centers,o ne of which is an all-carbon quaternary stereogenic center,i ng ood yield with high diastereo-and enantioselectivities.Scheme 1. Asymmetric Mannich-type reaction to construct vicinal quaternary stereogenic centers and structure of the chiral bis(guanidino)iminophosphorane 1.