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Asymmetric platinum group metal-catalyzed carbonyl-ene reactions: Carbon-carbon bond formation versus isomerization

Lookup NU author(s): Dr Simon Doherty, Dr Julian Knight, Catherine Smyth, Dr Ross Harrington, Emeritus Professor Bill Clegg

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Abstract

A comparative study of the carbonyl-ene reaction between a range of 1,1′-disubstituted or trisubstituted alkenes and ethyl trifluoropyruvate catalyzed by Lewis acid-platinum group metal complexes of the type [M{(R)-BINAP}]2+ (M = Pt, Pd, Ni; BINAP is 2,2′- bis(diphenylphosphino)-1,1′-binaphthyl) revealed subtle but significant differences in their reactivity. For instance, the palladium-based Lewis acid [Pd{(R)-BINAP}]2+ catalyzes the ene reaction between methylene cycloalkane to afford the expected α-hydroxy ester in good yield and excellent diastereo- and enantioselectivity. In contrast, under the same conditions, the corresponding [M{(R)-BINAP}]2+ (M = Pt, Ni) catalyzes isomerization of methylene cycloalkane and the ene reaction of the resulting mixture of methylene cycloalkane and 1-methylcycloalkene at similar rates to afford a range of α-hydroxy esters in high regioselectivity, good diastereoselectivity, and good to excellent enantioselectivity. In addition, [Pt{(R)-BINAP}]2+ also catalyzes postreaction isomerization of the ene product as well as consecutive ene reactions to afford a double carbonyl-ene product. The sense of asymmetric induction has been established by single-crystal X-ray crystallography, and a stereochemical model consistent with the formation of (S)-configured α-hydroxy ester has been proposed; the same model also accounts for the observed exo-diastereoselectivity as well as the level of diastereoselectivity. © 2006 American Chemical Society.


Publication metadata

Author(s): Doherty S, Knight JG, Smyth CH, Harrington RW, Clegg W

Publication type: Article

Publication status: Published

Journal: Journal of Organic Chemistry

Year: 2006

Volume: 71

Issue: 26

Pages: 9751-9764

ISSN (print): 0022-3263

ISSN (electronic): 1520-6904

Publisher: American Chemical Society

URL: http://dx.doi.org/10.1021/jo062023n

DOI: 10.1021/jo062023n

PubMed id: 17168594


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