Oxazolo[3,2-a]indoles, pyrrolo- and azepino-[1,2-a]indoles from 3H-indole 1-oxides and acetylenecarboxylic esters by skeletal rearrangements

Abstract

3H-Indole N-oxides 3 have been prepared from 3H-indoles 1 by hydride reduction followed by mchloroperbenzoic acid oxidation. Reaction of 3 with dimethyl acetylenedicarboxylate (DMAD) and with methyl propiolate (MP), give a variety of products, all apparently formed by rearrangement of the initial isoxazole 1,3-dipolar cycloadduct, with the type of reaction being dependent on the 2substituent in 3: the 2-phenyl derivative of 3 gives oxazolo[3,2-a]indoles 5, and when 3 posseses a methyl or methylene substituent at C-2, both DMAD and MP give pyrrolo[1,2-a]indoles 6, with the MP reactions also yielding an azepino[1,2-a]indole 7 in each case. The structures of the products have been established by spectroscopy with those of 5b and 7b being confirmed by X-ray crystallography.