Construction of Vicinal Quaternary Stereogenic Centers by Enantioselective Direct Mannich-Type Reaction Using a Chiral Bis(guanidino)iminophosphorane Catalyst

A novel asymmetric direct Mannich-type reaction of -iminophenylacetate esters with thionolactones, bearing a substituent at the -position, as a less acidic pronucleophile was developed. Using bis(guanidino)iminophosphorane as the chiral organosuperbase catalyst, the reaction afforded densely functionalized amino-acid derivatives having vicinal quaternary stereogenic centers, one of which is an all-carbon quaternary stereogenic center, in good yield with high diastereo- and enantioselectivities.