Stereospecific Synthesis of Natural (+)Blastmycinone and Its Three (2R)-Diastereomers

Natural (+)blastmycinone [(+)1a] and its three (2R)-diastereomers [(+)1b, (−)1c, and (−)1d] were synthesized through stereospecific routes via the corresponding (−)blastmycinolactol [(−)2a] and its diastereomeric hydroxylactones [(+)2b, (−)2c, and (−)2d] from methyl 4,6-O-benzylidene-3-C-butyl-3-deoxy-α-d-altropyranoside (4) prepared by the Grignard reaction of methyl 2,3-anhydro-4,6-O-benzylidene-α-d-mannopyranoside (3) with butylmagnesium chloride. By the synthesis the relative configurations of natural type of racemic blastmycinone and its all diastereomers were completely established.