Synthesis of 1-Deoxy-8,8a-di-epi-castanospermine, 1-Deoxy-6,7,8a-tri-epi-castanospermine and Formal Synthesis of Pumilotoxin 251D

An efficient synthesis of 1-deoxy-8,8a-di-epi-castanospermine and 1-deoxy-6,7,8a-tri-epi-castanospermine through the use of proline-catalyzed asymmetric a-aminoxylation of an N-Boc derivative of L-homoprolinal is reported. The configuration of the proline catalyst used for the asymmetric aminoxylation step ultimately controls the absolute configuration of three adjacent stereogenic centers in the final products. The method is also used to achieve a formal synthesis of Pumilotoxin 251D.