Collect. Czech. Chem. Commun. 1984, 49, 871-880

Preparation of 21,26,27-trinor-5α-cholest-23-en-25→20-olide from a propargyl synthone

Vladimír Pouzar, Pavel Drašar, Ivan Černý and Miroslav Havel

Institute of Organic Chemistry and Biochemistry, Czechoslovak Academy of Sciences, 166 10 Praha 6


Reaction of 21-nor-5α-pregnan-20-al (I) with propargylmagnesium bromide afforded two isomeric 21-nor-5α-chol-23-yn-20-ols (II and IV) whose absolute configuration at C(20) was determined by chemical correlation with the known 21-nor-5α-cholan-20-ols (VI and VII). Extension of the side-chain in the compound by one carbon atom gave (20R)-21,26,27-trinor-5α-cholest-23-yne-20,25-diol (XIV). The isomeric (20S)-diol XX was obtained by the same procedure from the alcohol IV. Alternative synthesis of the diols XIV and XX by reaction of the lithium salt of 1-methoxymethoxy-2-propyne with (20S)-20,21-epoxy-5α-pregnane (XV) and the (20R)-isomer XXI, respectively, gave only low yields. The diols XIV and XX were converted into the respective unsaturated lactones, i.e. (20R)-21,26,27-trinor-5α-cholest-23-en-25→20-olide (XVII) and (20S)-21,26,27-trinor-5α-cholest-23-en-25→20-olide (XXIII).