7α-alkylation, 7,7-bisalkylation,and reduction of the 20-oxo group of poststerone in reactions with alkyl halides in lithium–ammonia solution |
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Authors: | I V Galyautdinov Z R Sadretdinova O S Mozgovoi G G Gibadullina L M Khalilov Z S Muslimov V N Odinokov |
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Institution: | 1.Institute of Petrochemistry and Catalysis,Russian Academy of Sciences,Ufa, Bashkortostan,Russia |
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Abstract: | Reactions of poststerone with methyl iodide, allyl bromide, and propargyl bromide in lithium–ammonia solution resulted in its completely stereoselective 7α-alkylation accompanied by reduction of the 20-oxo group with formation of equimolar amounts of 20R- and 20S-hydroxy derivatives. The reaction of poststerone with excess allyl bromide afforded 7,7-bis-allyl 20R- and 20S-alcohols at a ratio of 3: 1. The reduction of the 20-oxo group in the alkylation of poststerone with excess propargyl bromide led to the formation of an equimolar mixture of Δ8(14)- and Δ8(9)-isomers with exclusive S configuration of C20. |
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