Phenyl acetylene, reaction with isocyanates

Sydnones can be regarded as cyclic azomethine imines and as such they undergo thermal cycloaddition reactions with a range of dipolarophiles. Thus, reaction with phenyl isocyanate converts 401 into 1,2,4-triazole 402. On photolysis, 3,4-diarylsydnones lose carbon dioxide and give nitrile imines, which can also be intercepted by dipolarophiles. Thermal reactions with acetylenic dipolarophiles lead to the formation of pyrazoles (Scheme 88) however, these reactions are rarely completely regioselective with unsymmetrical alkynes, e.g., <2000BKC761, 2000TL1687>. 

In reality, the second possibility occurred (57), and the same was true for the adducts containing other olefins. Finally, we verified the presence of hydroxyl in structure (IV) through reaction with phenyl isocyanate. Thus, the convincing experiments of Hoffmann, Middleton, and R. Adams were confirmed by our decisive evidence, so that 7T-structures were condemned to fade from the scene for these compounds. However, to emphasize the behavioristic similarity with the 77-complcxes, I suggested the term quasicomplex for the compounds which are formed from metallic salts and olefins or acetylenes through addition to the 7T-bond. A number of such quasi-complex compounds were obtained and studied by us. In particular, we showed that butadiene or its homologs, contrary to the earlier opinion of Sand, also formed the quasi-complex adducts in water, e.g.,... 

In the reaction of phenylacetylene with phenyl isocyanate in the presence of iron pentacar-bonyl hydantoine derivatives are obtained. More reactions of acetylenes with isocyanates... 

In contrast, cyanoynamines react with phenyl isocyanate via an initial [2+2] cycloaddition reaction across the CM3 bond of the isocyanate to give a quinoline derivative Intramolecular cobalt catalyzed cyclization of alkynes and isocyanates was employed in the total synthesis of camptothein, an antitumor alkaloid. The key step of the synthesis involves the reaction of the acetylene group-containing isocyanate 185 with the acetylene derivative 186 to give 187. ... 

Diphosphanylketenimines 102 are excellent 1,3-dipoles, which readily undergo regiospe-cific [3+2] cycloaddition reactions with suitable dipolarophiles, such as acetylenes, phenyl isocyanate and ethyl isothiocyanate. For example, reaction of 102 with two equivalents of acetylene derivatives form the cycloadducts 103. ... 

Corey-Fuchs reaction has also been employed to make pharmaceutically interesting compounds. The treatment of bromo-acetylene 20 with /-BuLi and the quench of resulting lithium alkylanide with phenyl isocyanate produced amide 21. After SEM removal, NMDA receptor antagonist 22 for stoke therapy was obtained. ... 

Analogously to ynamines and o, /3-acetylenic ketones, 4-aminobut-3-yn-2-ones react with 1,3-dipoles (68HCA443 73HCA2427 92KGS867). The reaction of 4-dimethylaminobut-3-yn-2-one with diphenylketene follows a route of [2-1-21-cycloaddition (30°C, THF, 1 h) to give 2-acetyl-3-dimethylamino-4,4-diphenyl-cyclobut-2-en-l-one (377) in 15% yield. With ethyl azidoformate (30°C, THF, 3 h), the tiiazole 378 is formed in 82% yield, whereas with phenyl isocyanate, the quinoline 379 is the product (by a [2- -4] scheme) in 70% yield (68HCA443). 

In this reaction phenyl isocyanate is generated in an exchange reaction of the diphenylcar-bodiimide with iron pentacarbonyl, and the unusual reaction product is formed from the carbodiimide, the isocyanate and two eqnivalents of the acetylene derivative. 

The alkenylidenecyclopropanes (104) and (105) react thermally with the electron-deficient acetylenes (106) exclusively in a [2 + 2] fashion to yield a mixture of the methylenecyclobutenes (107) and (108)." The preference for [2 -I- 2] addition in this reaction is in marked contrast to the course of the reaction between alkylidenecyclo-propanes and either 4-phenyl-1,2,4-triazolinedione or chlorosulphonyl isocyanate, neither of which gives any [2 -I- 2] addition products. 

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