HOFMANN CARBYLAMINE REACTION

The versatility of this method for the alkylation of compounds containing active methylene groups is illustrated by Table I. Review articles have recently appeared,34 and the application to the Hofmann carbylamine reaction is described in the following procedure in this volume, p. 96. 

HOFMANN CARBYLAMINE REACTION te ft-BUTYL ISOCYANIDE (2-Methylpropane, 2-isocyano)... 

Amino-4,6-bis(dimethylamino)-l,3,5-triazine has been converted by the Hofmann carbylamine reaction under phase-transfer conditions into 4,6-bis(dimethylamino)-2-isocyano-l,3,5-triazine... 

This reaction was first reported by Hofmann in 1868. It is the synthesis of isonitriles (also known as isocyanides) from primary amines and chloroform in the presence of alkali and is known as the Hofmann isonitrile synthesis, Hofmann carbylamine reaction, or Hofmann carbylamine synthesis. This reaction has been used to test the presence of primary amines from the order of isocyanides. Alternatively, the isonitriles can be prepared by means of the treatment of formamide of primary amines with toluenesulfonyl chloride" or phosphorus oxychloride (POCls)." Currently, the isonitriles have gained much attention in organic synthesis because of their application as versatile building blocks for heterocycles and in multicomponent reactions to generate combinatorial libraries, such as that in the Passerini reaction and Ugi reaction ... 

A series of isonitriles has been prepared by the Hofmann carbylamine reaction and several examples are recorded in Table 3.4. 

Dibromocarbene has been utilized in place of dichlorocarbene in the phase transfer Hofmann carbylamine reaction (see Sect. 3.5). Methyl and ethyl isocyanide are low boiling and separation of these products from residual chloroform is difficult. The purification can be facilitated by use of bromoform in these two cases (Eq. 4.8) [16]. 

The idea that dichlorocarbene is an intermediate in the basic hydrolysis of chloroform is now one hundred years old. It was first suggested by Geuther in 1862 to explain the formation of carbon monoxide, in addition to formate ions, in the reaction of chloroform (and similarly, bromoform) with alkali. At the end of the last century Nef interpreted several well-known reactions involving chloroform and a base in terms of the intermediate formation of dichlorocarbene. These reactions included the ring expansion of pyrroles to pyridines and of indoles to quinolines, as well as the Hofmann carbylamine test for primary amines and the Reimer-Tiemann formylation of phenols. 

The Hofmann carbylamine synthesis of isonitriles by the reaction of chloroform and base with primary amines was first reported over 100 years ago, but the reaction was not preparatively useful. For this reason, the two step process involving formyla-tion of the amine followed by dehydration was the method of choice. The phase transfer carbylamine reaction is inexpensive and convenient and the yields are such that it is competitive with the dehydration technique in many cases [13—15]. 

The realization that this was a new type of compound, isomeric to the nitriles, and the elaboration of the classical methods for the preparation of isocyanides, the alkylation method and the carbylamine method by Gautier and Hofmann, initiated an active period of isocyanide chemistry that ended by the turn of the century with Nef s investigations on the reactions of the formally divalent carbon atom in the isocyanides. - TTie discovery of the Passerini reaction in 1921 led to a brief renaissance of isocyanide chemistry. 

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