Issue in Honor of Prof. Armand Lattes ARKIVOC 2006 (iv) 90-118
5.7 Photoinduced decyanations Conclusions References Introduction
The use of the nitrile function for C-C bond formation reaction occupies an important position in organic chemistry. 1-4 Especially, deprotonation of the a-carbon and alkylation is an important reaction.5 The sequences involving the nitrile function usually requires the subsequent removal of the nitrile group in a convenient and clean manner. The reduction of the nitrile group (RCN) is observed with many reducing agents. Depending on the nature of the reducing agent and experimental conditions, the reaction can produce amines, aldehydes, primary alcohol, imines or alkanes (RCH3 or RH).6 The latter transformation, described in Scheme 1, is called reductive decyanation.
RCN
RH Scheme 1
In 1991, we discovered the anomalous reductive decyanation of a a-sulfonitrile induced by LiAlH4.7 We were then interested in the great variety of procedures allowing this transformation. We realized that, despite a large use of this reduction in organic synthesis these last years, no recent review focused on this topic.
This paper provides an overview of the different routes leading to decyanation. For each of them, experimental conditions and mechanistic aspects will be described. We describe also recent applications in organic synthesis. The purpose of this work is to point out the utility of this reaction through a set of examples. We concentrate on reductive decyanation of nitriles and will not discuss dehydrocyanation,8 oxidative decyanation9 or reactivity of cyanamides.10
1. Metal dissolving conditions Arapakos et al. using sodium biphenyl radical anion, sodium in liquid ammonia or lithiumethylamine solutions found that tertiary nitriles give reductive decyanation products in high yields.11-13 The mechanism proposed involves a two electrons transfer with formation of a carbanion via a radical anion. The latter is then protonated by ammonia in situ or by another proton donor depending on the reaction conditions (Scheme 2).11,14-16
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