Lewis acid mediated [2,3]-sigmatropic rearrangement of allylic alpha-amino amides |
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Authors: | Blid Jan Brandt Peter Somfai Peter |
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Institution: | Organic Chemistry, KTH Chemistry, Royal Institute of Technology, SE-100 44 Stockholm, Sweden. |
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Abstract: | Boron trifluoride and BBr(3) mediated 2,3]-sigmatropic rearrangements of allylic alpha-amino amides have been developed affording secondary amines in good yields. (E)-Crotyl and (E)-cinnamyl alpha-amino amides 2b and 2c exhibit excellent syn-diastereoselectivity upon rearrangement with either Lewis acid. The allylic amine 2a forms upon treatment with BF(3) or BBr(3) a five-membered heterocylic complex in which a single halide anion has been displaced by the carbonyl oxygen atom. The structures of the Lewis acid-amine complexes were elucidated using NMR spectroscopy. A plausible reaction mechanism, based on DFT calculations, is presented. Thus, BF(3)- or BBr(3)-complexed allylic amines 2 are shown to preferentially proceed, after deprotonation, via an endo transition state. |
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