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Allylic and allenic halide synthesis via NbCl(5)- and NbBr(5)-mediated alkoxide rearrangements.

ABSTRACT: Addition of NbCl(5) or NbBr(5) to a series of magnesium, lithium, or potassium allylic or propargylic alkoxides directly provides allylic or allenic halides. Halogenation formally occurs through a metalla-halo-[3,3] rearrangement, although concerted, ionic, and direct displacement mechanisms appear to operate competitively. Transposition of the olefin is equally effective for allylic alkoxides prepared by nucleophilic addition, deprotonation, or reduction. Experimentally, the niobium pentahalide halogenations are rapid, afford essentially pure (E)-allylic or -allenic halides after extraction, and are applicable to a range of aliphatic and aromatic alcohols, aldehydes, and ketones.

SUBMITTER: Ravikumar PC

PROVIDER: S-EPMC2754319 | biostudies-literature | 2009 Oct

REPOSITORIES: biostudies-literature

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Allylic and allenic halide synthesis via NbCl(5)- and NbBr(5)-mediated alkoxide rearrangements.

Ravikumar P C PC Yao Lihua L Fleming Fraser F FF

The Journal of organic chemistry 20091001 19

Addition of NbCl(5) or NbBr(5) to a series of magnesium, lithium, or potassium allylic or propargylic alkoxides directly provides allylic or allenic halides. Halogenation formally occurs through a metalla-halo-[3,3] rearrangement, although concerted, ionic, and direct displacement mechanisms appear to operate competitively. Transposition of the olefin is equally effective for allylic alkoxides prepared by nucleophilic addition, deprotonation, or reduction. Experimentally, the niobium pentahalide ...[more]

PMID: 19739606

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