An efficient diastereoselective reduction of α-alkyl-β-keto carbonitriles with TiCl 4 /BH 3 or LiBH 4 /CeCl 3 to syn- or anti-α-alkyl-β-hydroxy carbonitriles

α-Alkyl-β-keto carbonitriles can be reduced stereoselectively to syn- and anti-α-alkyl-β-hydroxy carbonitriles. The stereo-selectivity can be explained in terms of properties of the Lewis acid employed. TiCl 4 in noncoordinating solvents such as dichloromethane, followed by reduction with the borane/ pyridine complex, predominantly led to the syn-α-alkyl-β-hydroxy carbonitriles, according to a chelate transition state, whereas CeCl 3 in coordinating solvents such as THF, followed by reduction with LiBH 4 , predominantly led to the anti-isomers, in agreement with an open-chain transition state. The reduction to syn-α-alkyl-β-hydroxy carbonitriles is the first general preparation of these compounds. © Wiley-VCH Verlag GmbH, 2001.