Synthesis of 2-Arylindoles via Aza-ring Closure of Sulphonium Salts

Department of Chemistry, D. V. (P. G.) College, Orai-285 001 Manuscript received 23 September 1987, revised 6 January 1988, accepted 13 January 1988 MANY routes have been devised to synthesise 2- arylindoles, but the methods are not versatile because the reactions involve drastic reaction conditions. Hirroze et al.1 reported the reaction of N-phenacylpyridinium bromide with anilines to furnish 2-phenylindoles. Junjappa2 extended this reaction using phenacyldimethylsulphonium bromide. Bansal et al. 3,4 reported the synthesis of indole derivatives by the interaction of phenacylpyridinium and arsonium bromides. These workers suggested that the reaction occurred by the nucleophilic attack of amino group of aniline on the carbonyl group of pyridinium and arsonium salt to form an intermediate which underwent ylide formation; the latter subsequently cyclised to indole. These observations were in contrast to the suggestion of Junjappa2 who reported the course of reaction via an initial ylide intermediate. These contradictory observations led us to reinvestigate the course of reaction of sulphonium ylides and their salts with substituted anilines