The coupling of aryl and alkyl groups utilizing aldehyde arenesulfonylhydrazones and trialkylboranes

A series of aryl aldehyde arenesulfonylhydrazones were alkylated by trialkylboranes in the presence of base to produce the corresponding aryl alkanes in excellent yields. The aryl aldehyde tosylhydrazones and trisylhydrazones are readily prepared from the corresponding aryl aldehydes. The trisylhydrazones reacted more readily than the corresponding tosylhydrazones allowing many of the reactions to proceed at room temperature. The reaction tolerates a wide variety of functional groups, thereby allowing functionalized alkyl groups to be transferred. It gives good yields with secondary alkyI groups such as sec-butyl and cyclohexyl. The alkylation occurs with rigorously defined regioselectivity at the carbonyl carbon. Various blocked borane derivatives were studied and evaluated. Aryl ketones can also be utilized to give good yields of aryl alkanes. The mechanism of the reaction was also studied and is postulated to proceed via an organoborate complex at the original carbonyl carbon. This complex would undergo a 1,2-boratropic shift to produce a new trialkylborane. This new borane would then be hydrolyzed to the corresponding alkane by nucleophilic bases. This reaction is a useful new addition to the known reactions for the alkylation of carbonyl compounds and to the known reactions for the coupling of aryl and alkyI groups.