Regio- and Chemoselective Alkylation of 2,3-Dialkylindoles. A Convenient Preparation of 2,3,3-Trialkyl-3H-indoles

Various 3-alkyl-2.3-dimelhyl-3H-indoleswere prepared by addition of an alkyl iodide to a solution of the lithium salt of 2.3~dimelhylirldole.In contrast, reaction with ethyl chloroformate or trimethylsilyl chloride afforded the U-substituted indoles exclusively.The reaction failed with cyclohexylcarboxaldehyde.In connection with our interest in the cycloaddition chemistry of indoliurn metliylidesl~2 we required access to a variety of 2,3,3-trialkyl-3H-indoles (2).Although a number of routes to this system have been reporled.3the most common method appeared to be alkylation of the corresponding 2,3-dialkylindole magnesium salt4 (1) (Scheme 1).Scheme 1