III. Nitriles

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A. Synthesis

When t-butyl isonitrile reacts with a carbon-centered radical, an addition-elimination process takes place that results in the formation of a nitrile (Scheme 8).^16–23 This type of nitrile synthesis is illustrated by the reaction shown in eq 5.²⁰ (Scheme 10 in Chapter 2 describes another example of this type of reaction.²²)

II16(5).png

B. Reactions

1. Addition to a Cyano Group

Radical reactions of carbohydrate nitriles usually involve internal addition in which a carbon-centered radical generated in close proximity to a cyano group forms a new ring system.^24–31 An example is shown in Scheme 9, where the radical centered on C-6 in 11 adds to the cyano group as a part of this sequential process.²⁴ Carbohydrate radical formation in this type of reaction typically begins with the tri-n-butyltin radical abstracting a halogen atom or an O-thiocarbonyl group. After cyclization, the radical abstracts a hydrogen atom from Bu₃SnH to produce an imine, which in some cases is isolated and in others is hydrolyzed to the corresponding carbonyl compound before isolation.

2. Cyano Group Migration

When a cyclic imino radical forms during carbon-centered radical addition to a cyano group, the possibility exists that ring opening will lead to cyano group migration (Scheme 10).^32–34 Such a reaction is shown in Scheme 11, where migration accompanies ring opening of a benzylidene acetal.³²