Scope and Regiochemical Control of the Allylpotassium Reaction in the Synthesis of Sterols with Unsaturated Side Chains

Article abstract of DOI:10.1021/jo00270a021

Allylpotassium derivatives were prepared from a variety of olefins by using Schlosser's base (BuLi/KOt-Bu).Reaction with (20S)-20-(iodomethyl)pregnane i-methyl ether (1) followed by deprotection gave in high yields a wide variety of Δ²⁴ and Δ²⁴⁽²⁸⁾ sterols, including the naturally occuring desmosterol (37), fucosterol (33), 24(E)-propylidenecholesterol (35), 24-methylenecholesterol (3), dehydroaplysterol (10), 25-methyl-24-methylenecholesterol (11), mutasterol (12), and 25-methylxestosterol (13).Control of the regiochemistry of unsymmetrical allylmetals was achieved through the addition of Li2CuCl3.Rules concerning the high regioselectivities and stereoselectivities are discussed.