Syntheses of Key Synthetic Intermediates of Active Vitamin D. of 1 a, 3 /3-Diacetoxy-5, 7-choladiene Derivatives? Central Research

Abstract

Steroidal synthons for the preparation of active forms of vitamin D were synthesized.1 α, 3β-Diacetoxy-23, 24-dinor-5, 7-choladien-22-ol [1] was prepared starting from 22-acetoxy23, 24-dinor-1, 4, 6-cholatrien-3-one C 5 J. Enolization of [5] with isopropenyl acetate under acidic conditions, reduction of the tetraenyl acetate C 7 J with Ca(BH, ), and the treatment of the trienol [9] with PTAD (4-phenyl-3 H-1, 2, 4-triazole-3, 5(4 H)-dione) gave a DielsAlder adduc[111]. Protection of the hydroxyl group of [11] as a t-butyldimethylsilyl ether and the conversion of the acetyl group of [13] into tetrahydropyranyl ether produced [17]Epoxidation of [17] with m-CPBA and removal of the t-butyldimethylsilyl group of [19] with n-Bu4NF followed by the reduction with LiA1H4 gave the 1 a, 3 p-diol [23]. Acetylation of [23] and cleavage of the tetrahydropyranyl group of [25] yielded the target compound C 1 1 Alternatively, [13] was converted into 1 1 J in six steps through the trityl ether [31]. In a similar manner, 24-acetoxy-1, 4, 6-cholatrien-3-one[6] was transformed into 1α, 3α-diacetoxy-5, 7-choladien-24-ol C 3 J. The compounds 1 J and [3] were oxidized with pyridinium chlorochromate to afford the corresponding aldehydes [2] J and [4] .