alpha -Alkyl-beta -keto carbonitriles can be reduced stereoselectively to syn- and anti-alpha -alkyl-beta -hydroxy carbonitriles. The stereoselectivity can be explained in terms of properties of the Lewis acid employed. TiCl4 in noncoordinating solvents such as dichloromethane, followed by reduction with the borane/pyridine complex, predominantly led to the syrz-alpha -alkyl-beta -hydroxy carbonitriles, according to a chelate transition state, whereas CeCl3 in coordinating solvents such as THF, followed by reduction with LiBH4, predominantly led to the anti-isomers, in agreement with an open-chain transition state. The reduction to syn-alpha -alkyl-beta -hydroxy carbonitriles is the first general preparation of these compounds
An Efficient Diastereoselective Reduction of alfa-Alkyl-beta-keto Carbonitriles with TiCl4/BH3 or LiBH4/CeCl3 to syn- or anti-alfa-Alkyl-beta-hydroxy Carbonitriles
DE NINO, Antonio;DALPOZZO R;
2001
Abstract
alpha -Alkyl-beta -keto carbonitriles can be reduced stereoselectively to syn- and anti-alpha -alkyl-beta -hydroxy carbonitriles. The stereoselectivity can be explained in terms of properties of the Lewis acid employed. TiCl4 in noncoordinating solvents such as dichloromethane, followed by reduction with the borane/pyridine complex, predominantly led to the syrz-alpha -alkyl-beta -hydroxy carbonitriles, according to a chelate transition state, whereas CeCl3 in coordinating solvents such as THF, followed by reduction with LiBH4, predominantly led to the anti-isomers, in agreement with an open-chain transition state. The reduction to syn-alpha -alkyl-beta -hydroxy carbonitriles is the first general preparation of these compoundsI documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
