Addition reactions of heterocyclic compounds. Part XLVII. Formation of benzazepines from indoles with dimethyl acetylenedicarboxylate in acetonitrile; crystal structure of dimethyl 2,3-dihydro-2-indol-3-ylbenz[b]azepine-3,4-dicarboxylate

Abstract

1-Methylindole reacts with dimethyl acetylenedicarboxylate in pure acetonitrile to give dimethyl 1-methylbenz[b]azepine-3,4-dicarboxylate. This undergoes a Diels–Alder addition across the 2- and 5-positions with one further mol. equiv. of the acetylene, and with 1-methylindole and acid gives dimethyl 2,3-dihydro-1-methyl-2-(1-methylindol-3-yl)benz[b]azepine-3,4-dicarboxylate. Treatment of indole with the acetylenic ester in acetonitrile only gives the corresponding 2,3-dihydro-2-(indol-3-yl)benzazepine (18), the structure of which has been confirmed by an X-ray diffraction study. Crystals of (18) are triclinic, a= 10·46, b= 11·50, c= 8·85 Å, α= 91·5, β= 114·6, γ= 106·2, space group P. The structure was refined to R 11·4% for 2989 independent reflections. Some reduction products of these azepines are described, and their mode of formation is discussed.