An Efficient Asymmetric Synthesis of 1α,25-(OH)2 Vitamin D3 A-Ring Synthon

Article abstract of DOI:10.1021/jo00061a028

Chiral synthesis of the A-ring synthon 3 of 1α,25-dihydroxyvitamin D₃ (1a) based on palladium-catalyzed cyclization of 8-bromo-2,8-nonadienoates is described.Reaction of (E)-4b and (Z)-4d in the presence of Pd(OAc)2, PPh3 and K2CO3 gave (E)-3b and (Z)-3d, respectively.Optically active 4d was prepared from 24 by asymmetric aldol reaction using 31, which was cyclized to 3d.With further reactions, 1α,25-dihydroxyvitamin D₃ (1a) was obtained.