Highly Enantioselective Direct Reductive Coupling of Conjugated Alkynes and α-Ketoesters via Rhodium-Catalyzed Asymmetric Hydrogenation

Jong-Rock Kong, Ming-Yu Ngai, and Michael J. Krische*
Department of Chemistry and Biochemistry, University of Texas at Austin, Austin, Texas 78712
J. Am. Chem. Soc., 2006, 128 (3), pp 718–719
DOI: 10.1021/ja056474l
Publication Date (Web): December 22, 2005
Copyright © 2006 American Chemical Society
*

In papers with more than one author, the asterisk indicates the name of the author to whom inquiries about the paper should be addressed.

, mkrische@mail.utexas.edu

Abstract

Abstract Image

Catalytic hydrogenation of 1,3-enynes 1a−7a in the presence of ethyl pyruvate and related activated ketones using chirally modified cationic rhodium catalysts results in reductive coupling to afford dienylated α-hydroxy esters 1b−7b and 3c−3f with exceptional levels of regio- and enantiocontrol. These studies represent the first highly enantioselective direct catalytic reductive couplings of alkynes to ketones. As illustrated by the conversion of 6b to 6c−6h, the diene containing the side chain of the coupling products is subject to diverse chemo- and regioselective manipulation. Reductive coupling of enyne 6a and ethyl pyruvate using elemental deuterium provides the monodeuterated product deuterio-6b, consistent with a catalytic mechanism involving alkyne−carbonyl oxidative coupling followed by hydrogenolytic cleavage of the resulting oxametallacycle, as corroborated by ESI−MS analysis.

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History

  • Published In Issue January 25, 2006
  • Received September 20, 2005

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