Aldehydes from Nitriles. Formation of N-Alkylnitrilium Ions and Their Reduction to N-Alkylaldimines by Organosilicon Hydrides

Article abstract of DOI:10.1021/jo00316a023

A two-step procedure for the partial reduction of nitriles to aldehydes under mild reaction conditions is presented.This approach involves the N-alkylation of nitriles in dichloromethane solution and reductive capture of the resulting nitrilium ions to N-alkylaldimines with an organosilicon hydride such as triethylsilane or tri-n-hexylsilane.Mild hydrolysis of the aldimines produces aldehydes in generally good-to-excellent yield.Use of both triethyloxonium tetrafluoroborate and isopropyl chloride-iron(III) chloride reagents to effect alkylation is reported.Selective reduction of the nitrile function in polyfunctional substrates is possible with this technique.Over reduction to amines does not occur.Close control of reducing agent and reaction temperatures is not required.Attempts to effect reduction of nirile-boron trifluoride complexes with triethylsilane were unsuccessful, even at elevated temperatures.