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J Am Chem Soc. 2010 Feb 10;132(5):1685-9. doi: 10.1021/ja909073r.

Nazarov cyclizations of an allenyl vinyl ketone with interception of the oxyallyl cation intermediate for the formation of carbon-carbon bonds.

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1
Department of Chemistry, Dalhousie University, Halifax, Nova Scotia B3H 4J3, Canada.

Abstract

Treatment of an allenyl vinyl ketone with BF(3) x Et(2)O leads to a cyclic oxyallyl cation by a Nazarov reaction, and when this reaction is conducted in the presence of an acyclic diene, [4 + 3] and [3 + 2] products are obtained efficiently with high regio- and stereoselectivity. The proportion of [4 + 3] to [3 + 2] product depends on the substitution on the diene. Cyclic dienes react with the oxyallyl cation by forming only one carbon-carbon bond, but the site of bond formation can be affected by steric hindrance. Electron-rich alkenes intercept the allyl cation by forming one carbon-carbon bond, or two carbon-carbon bonds through [3 + 2] cyclization. In some instances, further treatment of the initial products with BF(3) x Et(2)O leads to equilibrated products in good yield.

PMID:
20078119
DOI:
10.1021/ja909073r
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