A glycal approach towards an efficient and stereodivergent synthesis of polyhydroxypyrrolidines

A stereo-defined synthesis of two diastereomers of polyhydroxypyrrolidines from 3,4,6-tri-O-benzyl-d-glucal involving a cleavage–recyclization strategy is reported. Hemiacetal obtained from glucal , upon reduction with LiAlH4 afforded diol . Selective acetylation of to , followed by Mitsunobu cyclization yielded the diversely protected polyhydroxypyrrolidine . Oxidation of and subsequent stereoselective reduction led to , the C-5 epimer of , which upon Mitsunobu cyclization gave polyhydroxypyrrolidine . Selective deprotection of the acetyl groups of and were carried out using Na2CO3 in MeOH. Polyhydroxypyrrolidines and upon heating with an excess of Mg in MeOH underwent simultaneous N-detosylation and deacetylation to afford amino alcohols and , respectively, in quantitative yield. Catalytic hydrogenation of and provided quantitatively the polyhydroxypyrrolidines and , respectively.