Abstract
Chemical syntheses of two series of vitamin D analogues, based on the modification of hydroxy groups either in the A-ring or in the side chain of vitamin D, are reviewed. The C4-functionalized stereoisomeric analogues of vitamin D, in which a spiro-oxetane structure exists at the C2 position of the A-ring, were synthesized in a convergent manner. The absolute configuration at the C4-position of the synthesized compounds was determined by the circular dichroism exciton chirality method using the corresponding C4-benzoates. The side chain analogues having m- or p-substituted benzoic acid were also convergently prepared from the requisite CD-ring synthons using turbo-Grignard reagents, which allowed aromatic side chain with a polar functional moiety to be installed in a single step with excellent yield.
