Iridium-Catalyzed C−C Bond Forming Hydrogenation:  Direct Regioselective Reductive Coupling of Alkyl-Substituted Alkynes to Activated Ketones

Ming-Yu Ngai, Andriy Barchuk, and Michael J. Krische*
Department of Chemistry and Biochemistry, University of Texas at Austin, Austin, Texas 78712
J. Am. Chem. Soc., 2007, 129 (2), pp 280–281
DOI: 10.1021/ja0670815
Publication Date (Web): December 21, 2006
Copyright © 2007 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

We report the first hydrogen-mediated C−C bond formations catalyzed by iridium. Hydrogenation of commercially available alkyl-substituted alkynes, 3-hexyne 1a and 1-phenylpropyne 1b, in the presence of α-ketoesters 2a−2g using cationic iridium precatalysts results in reductive C−C coupling to afford β,γ-unsaturated α-hydroxyesters 3a−3f and 4a−4e and 4g, which are formed in excellent yield, with complete control of olefin geometry and, in most cases, with excellent regiocontrol. Similar levels of selectivity are observed across a range of alkynes 1c−1h. Reductive coupling of 3-hexyne 1a and α-ketoester 2a under an atmosphere of elemental deuterium provides the monodeuterated product deuterio-3a, consistent with a catalytic mechanism involving alkyne−carbonyl oxidative coupling followed by hydrogenolysis of the resulting oxametallacycle.

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History

  • Published In Issue January 17, 2007
  • Received October 3, 2006

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