Diastereoselective cyclopropanation of medium and large ring alpha, beta-unsaturated homochiral ketals and enantioselective synthesis of (-)-modhephene.
AuthorMath, Shivanand Kumarswamy.
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PublisherThe University of Arizona.
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AbstractA general straightforward synthetic approach for the enantioselective construction of medium and large ring cyclopropyl ketones via diastereoselective Simmons-Smith cyclopropanation is discussed. Medium and large 2-cycloalkenone 1,4Di-O-benzyl-L-threitol ketals undergo efficient and diastereoselective cyclopropanation when treated with an excess of the Simmons-Smith reagent. The cyclopropyl ketals are obtained in 80-94% with >23:1-8:1 diastereoselectivity. The first enantioselective synthesis of (-)-modhephene, a natural product possessing the carbocyclic (3.3.3) propellane skeleton, by the use of diastereoselective cyclopropanation methodology is described.