The chemistry of the isocyanides3 began when, in 1859 Lieke19 formed allyl iso-cyanide from allyl iodide and silver cyanide, and when, in 1866 Meyer20 produced in the same way 1-isocyano-1-desoxy-glucose. In 1867, Gautier21a used this procedure to prepare alkylisocyanides, and Hofmann22 introduced the formation of isocyanides from primary amines, chloroform, and potassium hydroxyde. Gautier3,21b also tried to prepare an isocyanide by dehydrating an amine formiate via its formylamine using phosphorus pentoxide, but this process produced no isocyanide. Gautier had not yet realized that acidic media destroyed the isocyanides.
However, for a whole century the chemistry of the isocyanides remained as a rather empty part of organic chemistry, since they were not yet easily available, and furthermore they had a very unpleasant smell. At that time, only 12 isocya-nides had been prepared and only a few of their reactions had been investigated.3
In the 1890s, Nef23 mentioned that the functional group —NC of the isocya-nides contains a divalent carbon atom CII, and therefore there is a large difference between their chemistry and that of the other chemical compounds that contain only tetravalent carbon atoms CIV. Any synthesis of isocyanides corresponds to a conversion of CIV into Cn, and all chemical reactions of isocyanides correspond to transitions of the carbon atoms CII into CIV.
In this period, the most important reactions of the isocyanides were the formations of tetrazole derivatives from isocyanides and hydrazoic acid, a process introduced in 1910 by Oliveri-Mandala and Alagna,24 and then in 1921 Passerini introduced the reaction (P-3CR),25 which was the first 3-component reaction of the isocyanides. In the 1940s Baker,26 and later Dewar,27 proposed mechanisms of the P-3CR. The important role of the intermediate hydrogen bond between the carboxylic acid and the carbonyl compound in suitable solvents was mentioned.4
In 1948, Rothe4,28 discovered the first naturally occurring isocyanide in the Penicillum notatum Westling and in the Penicillum chrysogenum. This compound was soon used as the antibiotic xanthocillin 5a. Later Hagedorn and Tonjes29 prepared its O,O' -dimethylether of xanthocillin 5b by dehydrating its N,N'-diformylamine with phenylsulfonylchloride in pyridine (Scheme 1.2). Since
Scheme 1.2 Xanthocillin.
1973 an increasing number of naturally occurring isocyanides has been found in plants and living cells.30
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