Nitriles imidoyl halide synthesis

Acid amide-triphenylphosphine dihalide adducts (4) have found wide application in organic synthesis. - Synthetic equivalents are adducts (5) from acid amides and triphenylphosphine/CCU, which are prepared in situ from the educts. - With these reagents the following transformations have been performed dehydration of amides or aldoximes to nitriles, preparation of isonitriles from secondary form-amides, preparation of imidoyl halides from amides or acylhydrazines and preparation of ketene imines from amides. Using polymer-supported triphenylphosphine the work-up procedure is much easier to achieve. Triphenylphosphine can be replaced by tris(dialkylamino)phosphines. - Instead of CCI4 hexa-chloroethane, hexabromoethane or l,l,2,2-tetrabromo-l,2-dichloroethane can be used " the adducts thus formed are assumed to be more effective than those from the triphenylphosphine/CCU system. 

Symmetrical six-membered triazine rings can be synthesized from C-N units which are parts of nitrile groups, imidoyl halides, ureas, imido esters, amidines and guanidines. These reactants may be generated during the synthesis. 

Phosphanes are widely used as reagents in organic synthesis, triphenylphos-phane being the most commonly applied due to its stability towards oxidation. The polymer-supported analog has so far found use in the transformation of alcohols into alkyl halides and acids into acid halides, using either carbon tetrachloride or carbon tetrabromide as the halogen source (Scheme 6.4) [7, 11-14], This system can also successfully transform primary amides and oximes into nitriles, whereas secondary amides are transformed into imidoyl chlorides (Scheme 6.5) [15],... 

Triphenylphosphine-carbon tetrahalides. 13, 331-332 15, 352 16, 366-368 Acid halides. The relatively mild conditions of converting acids to halides by Ph3P-CX4 can be exploited for a one-flask synthesis of A-methoxy imidoyl bromides, which give rise to nitriles on photolysis. In the presence of EtsN the PhsP-CX4 combination converts amines and CF3COOH to trifluoroacetimidoyl halides. ... 

The classical example of this type of reaction is the v. Braun method of degradation, by which a secondary amine can be transformed into a primary amine, and finally into ammonia, via the imidoyl chloride intermediates. This reaction has been used for the structure elucidation of alkaloids. Although degradative studies are not conducted to any extent today due to the convenience of spectral methods, the v. Braun elimination is still used in organic synthesis to prepare nitriles as well as alkyl halides. 

The thermal elimination of alkyl halides to form nitriles is perhaps the best known reaction of imidoyl chlorides. J. v. Braun investigated this reaction in detail over a period of 40 years, and he developed a host of useful new synthetic procedures for the synthesis of compounds, which are otherwise more difficult to obtain. Unfortunately, most of his work has been written up in detailed form in Chemische Berichte and it requires some effort to retrieve this information. However, he wrote one review article in 1934 which is most informative. The elimination of alkyl halides on heating of imidoyl chlorides was recognized by Wallach in 1877 and v. Pechmann and Ley and Holzweissig reported examples of this reaction prior to the work of J. v. Braun. The elimination reaction, in its most general terms, can be described by the following sequences ... 

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