Research and Development of an Efficient Synthesis of a Key Building Block for Anti-AIDS Drugs by Diphenylprolinol-Catalyzed Enantio- and Diastereoselective Direct Cross Aldol Reaction

Abstract

An efficient method for synthesizing 1-({[(3R,3aS,6aR)-hexahydrofuro[2,3-b]furan-3-yloxy]carbonyl}oxy)pyrrolidine-2,5-dione (1), a key building block for HIV protease inhibitors, has been developed. A diphenylprolinol-catalyzed highly enantio- and diastereoselective cross aldol reaction of polymeric ethyl glyoxylate with an aldehyde was used as the key step. Acetalized aldol adduct was reduced with NaBH4 to give the diol intermediate in quantitative yield. The acetal exchange reaction followed by hydrogenation with Pd/C catalyst afforded 1′ in 95% yield over 2 steps. The condensation of 1′ with a carbonate gave crystalline 1 (>99/1 dr, > 99% ee) after single crystallization. This is a highly practical synthetic method since environmentally benign organocatalysis is utilized, the amount of catalyst is reduced to 3 mol %, and all of the intermediates before 1′ can be used without any purification.