Technical Library

Doyle and West72 demonstrated the acid-catalyzed reduction of alkyl-substituted cyclohexanones with di-tert-butylsilane, di-tert-butylmethylsilane and tri-tert-butylsilane to proceed with predominant formation of the less stable isomer as the trifluoroacetate. For example, 4-tertbutylcyclohexanone gives 67% of the cis-4-tert-butylcyclohexyl trifluoroacetate.

The reduction of 4-tert-butylcyclohexanone with triethylsilane or dimethylphenylsilane preferentially gives the trans product. Very high trans to cis stereoselectivity of this transformation with triethoxysilane and TBAF was reported as was the reduction of 3-phenyl-2-butanone to anti 3-phenyl-2-butanol.73

The stereoselective silane reduction of β-hydroxy ketones with diisopropylchlorosilane has been demonstrated.74-76

A very efficient asymmetric reduction of arylalkyl ketones has been shown. The reaction, which does not work well for prochiral dialkyl ketones, is carried out with PMHS in the presence of a chiral titanium catalyst.77

The highly diastereoselective reduction of oximes has been reported.57 The diastereoselectivity was much higher than that reported for the corresponding reduction with lithium aluminum hydride in diethyl ether.

Buchwald and coworkers78 have reported the reduction of imines in very high enantiomeric excess through the use of a titanium catalyst activated with phenylsilane and the reduction with polymethylhydrosiloxane or phenylsilane.

The Lewis acid-catalyzed triphenylsilane reduction of hemiketals was shown to occur with high stereoselectivity.79

The tri-n-butyltin hydride reductions are well-known and have been reviewed.80 A recent report shows that tri-n-butyltin hydride can provide the hydrogen for the reductive amination of ketones and aldehydes, thus providing an alternative to sodium cyanoborohydride for this transformation.81 This same transformation was reported using polymethylhydrosiloxane as the reducing agent.82

Triphenylgermane has been shown to reduce acid chlorides to aldehydes with palladium(0) catalysis.83

Tri-n-butylgermane has been employed in the reductive alkylation of active olefins, in particular acrylonitrile.84