Phenylacetylene, reaction with ethyl chloride

Interesting publications of work undertaken in this field of reactivity by a research group in (what at that time was part of) the USSR, unfortunately, was published mainly in rather inaccessible journals. The rates of reaction of phenylacetylene with ethyl- and phenylmagnesium bromide were measured in diethyl ether and in tetrahydrofuran, respectively [32]. The results, presented in Table 8, clearly show the dramatic change in the second-order rate constants, when diethyl ether is replaced by tetrahydrofuran as the solvent. The same effect had been found in 1968 by others [33] for the reaction of benzylmagnesium chloride with phenylacetylene at 0°C the second-order rate constant (/c2 X 10 L mol sec ) was 0.008 in diethyl ether and 84 in tetrahydrofuran, a change by a factor of (more than) 10 thousand. 

The direct combination of selenium and acetylene provides the most convenient source of selenophene (76JHC1319). Lesser amounts of many other compounds are formed concurrently and include 2- and 3-alkylselenophenes, benzo[6]selenophene and isomeric selenoloselenophenes (76CS(10)159). The commercial availability of thiophene makes comparable reactions of little interest for the obtention of the parent heterocycle in the laboratory. However, the reaction of substituted acetylenes with morpholinyl disulfide is of some synthetic value. The process, which appears to entail the initial formation of thionitroxyl radicals, converts phenylacetylene into a 3 1 mixture of 2,4- and 2,5-diphenylthiophene, methyl propiolate into dimethyl thiophene-2,5-dicarboxylate, and ethyl phenylpropiolate into diethyl 3,4-diphenylthiophene-2,5-dicarboxylate (Scheme 83a) (77TL3413). Dimethyl thiophene-2,4-dicarboxylate is obtained from methyl propiolate by treatment with dimethyl sulfoxide and thionyl chloride (Scheme 83b) (66CB1558). The rhodium carbonyl catalyzed carbonylation of alkynes in alcohols provides 5-alkoxy-2(5//)-furanones (Scheme 83c) (81CL993). The inclusion of ethylene provides 5-ethyl-2(5//)-furanones instead (82NKK242). The nickel acetate catalyzed addition of r-butyl isocyanide to alkynes provides access to 2-aminopyrroles (Scheme 83d) (70S593). 

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