Collect. Czech. Chem. Commun. 1998, 63, 1575-1588

Towards Synthesis of Calysterols, Marine Sterols with Cyclopropene Moiety in the Side Chain: Synthesis of 26,27-Dinor-23H-isocalysterol

Alicja Kurek-Tyrlik, Kazimierz Minksztym and Jerzy Wicha

Institute of Organic Chemistry, Polish Academy of Sciences, ul. Kasprzaka 44, 01-224 Warsaw, Poland


26,27-Dinor-23H-isocalysterol 24 has been synthesized in 19% yield (6 steps) from ethyl 6β-methoxy-3α,5-cyclo-5α-pregnan-21-oate (18). For construction of the side chain, alkylation of lithium salt of ester 18 with 1-bromo-1,2-dimethyl-c-3-iodomethyl-c-2-(trimethylsilyl)cyclopropane 16 was used. It has been shown that reduction of the ester group in position 21 and rearrangement of the 3,5-cyclosteroid system are compatible with the sidechain functionalities. It has been found that methylation of 1,1-dibromo-2-(trimethylsilyl)cyclopropane is accompanied by an rearrangement involving 1,2-migration of the trimethylsilyl group.

Keywords: Steroids; Cyclopropanes; Cyclopropenes; Steroid side chain construction; Marine natural products; Total synthesis.