Mechanism and scope of the cyanide-catalyzed cross silyl benzoin reaction.
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.
Linghu
Xin
X
Department of Chemistry, University of North Carolina, Chapel Hill, NC 27599-3290, USA.
Bausch
Cory C
CC
Johnson
Jeffrey S
JS
D000215:Acylation; D000447:Aldehydes / Q000737:chemistry*; D001573:Benzoin / Q000737:chemistry*; D002384:Catalysis; D043844:Crown Ethers / Q000737:chemistry; D011190:Potassium Cyanide / Q000737:chemistry*; D012821:Silanes / Q000737:chemistry; D014867:Water / Q000737:chemistry
D000447:Aldehydes; D043844:Crown Ethers; D012821:Silanes; D014867:Water; D001573:Benzoin; D011190:Potassium Cyanide