49 ステロイド側鎖およびC D環の立体選択的合成

概要

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(±)-De-AB-Cholestan-9-one (1) and (±)-De-AB-Cholest-8(14), 22-diene-9-one (22) were prepared as a synthetic precursor for various steroids. In the Synthesis of 1 three important reactions are involved. The first one is the highly stereoselective Claisen rearrangement of the allyl alcohol 9b to introduce the trans stereo-chemistry between C(13)methyl and C(14)hydrogen and the geometry of 17(20)E-olefin. The second one is an efficient intramolecular alkylation of C(9)acyl carbanion to construct steroidal C-ring. The third one is the stereospecific alkylation (SN2) of the secondary tosylate 2 by the protected cyanohydrin 16 to introduce the asymmetric center at C(20). These overall transformations provide the required stereochemistry at C(13), C(14), C(17) and C(20) in 1. The key reaction in the synthesis of 22 was a highly stereo-selective Michael addition of the organocopper reagent 28 in which C(23)allyl alcohol moiety serves to control the stereochemistry at C(17) and C(13) (cis-stereochemistry between C(13)methyl and C(17) side-chain). C(20)methyl was introduced stereoselectively by combination of Claisen rearrangement and decarbonylation. The stereoselectivity of the Michael addition reaction was, moreover, examined under various conditions.
天然有機化合物討論会の論文
1981-09-10