Mechanism and Scope of the Cyanide-Catalyzed Cross Silyl Benzoin Reaction

Xin Linghu, Cory C. Bausch, and Jeffrey S. Johnson*
Contribution from the Department of Chemistry, University of North Carolina, Chapel Hill, North Carolina 27599-3290
J. Am. Chem. Soc., 2005, 127 (6), pp 1833–1840
DOI: 10.1021/ja044086y
Publication Date (Web): January 19, 2005
Copyright © 2005 American Chemical Society

Abstract

Abstract Image

In this work, cross silyl benzoin addition reactions between acylsilanes (1) and aldehydes (2) catalyzed by metal cyanides are described. Unsymmetrical aryl-, heteroaryl-, and alkyl-substituted benzoin adducts can be generated in moderate to excellent yields with complete regiocontrol using potassium cyanide and a phase transfer catalyst. From a screen of transition metal cyanide complexes, lanthanum tricyanide was identified as an improved second-generation catalyst for the cross silyl benzoin reaction. A study of the influence of water on the KCN-catalyzed cross silyl benzoin addition revealed more practical reaction conditions using unpurified solvent under ambient conditions. A sequential silyl benzoin addition/cyanation/O-acylation reaction that resulted in two new C−C bonds was achieved in excellent yield. The mechanism of cross silyl benzoin addition is proposed in detail and is supported by crossover studies and a number of unambiguous experiments designed to ascertain the reversibility of key steps. No productive chemistry arises from cyanation of the more electrophilic aldehyde component. Formation of the carbon−carbon bond is shown to be the last irreversible step in the reaction.

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History

  • Published In Issue February 16, 2005
  • Received September 28, 2004

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