A Short, Efficient Copper-Mediated Synthesis of 1α,25-Dihydroxyvitamin D<sub>2</sub> (1α,25-Dihydroxyergocalciferol) and C-24 Analogs<sup>1</sup><sup>,</sup><sup>2</sup>
作者:Mercedes Torneiro、Yagamare Fall、Luis Castedo、Antonio Mouriño
DOI:10.1021/jo970604u
日期:1997.9.1
Two synthetic routes to the nonnatural hormone 1 alpha,25-dihydroxyergocalciferol [2b, 1 alpha,25-(OH)(2)-D-2] and analogs modified at C-24 have been developed both starting from aldehyde 7b. Key steps in route A (eight steps, approximate to 38% overall yield from 7b) are (1) stereoselective addition of (E)-vinyllithium reagent 8c to aldehyde 7b; and (2) S(N)2' anti-displacement of the allylic phosphate of 5e by organocuprates derived from Grignard reagents and CuCN in the presence of LiCl. Key steps in route B (eight steps from 7b, 48% overall yield) are (1) Wittig-Horner type coupling between ketone 22, which bears an allylic phosphate group on the side chain, and the ylide derived from the Lythgoe-Roche phosphine oxide to form the vitamin D triene unit; and (2) efficient S(N)2' anti-displacement of the phosphate group of 23 by the organocuprate derived from MeMgCl, CuCN, and LiCl, without affecting the labile vitamin D triene system, to give, after deprotection, 1 alpha,25-(OH)2-D-2. Route B is particularly attractive as an approach to diverse C-24 vitamin D analogs for biological screening.