Chemo- and diastereoselective cyclopropanation of allylic amines and carbamates |
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Authors: | Kristí na Csatayová ,James A. Lee,Kenneth B. Ling,Paul M. Roberts,Angela J. Russell,James E. Thomson |
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Affiliation: | Department of Chemistry, Chemistry Research Laboratory, University of Oxford, Mansfield Road, Oxford OX1 3TA, UK |
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Abstract: | A highly chemo- and diastereoselective protocol for the cyclopropanation of tertiary allylic amines with Shi’s carbenoid [CF3CO2ZnCH2I] is described. The high levels of diastereoselectivity observed in these reactions may be attributed to chelation of the nitrogen atom to the zinc reagent, which then transfers a methylene unit to the syn-face of the olefin. Furthermore, a stereodivergent protocol for the cyclopropanation of a range of allylic carbamates has been developed, which provides access to both diastereoisomers of the corresponding cyclopropanes with very high levels of diastereoselectivity: cyclopropanation with the Wittig-Furukawa reagent [Zn(CH2I)2] proceeds under chelation control to give the corresponding syn-product, whilst reaction with Shi’s carbenoid proceeds under steric control to give the corresponding anti-cyclopropane, in >95:5 dr in both cases. |
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Keywords: | Cyclopropanation Allylic amines Allylic carbamates Simmons-Smith Shi&rsquo s carbenoid |
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