Interaction of 1,2,3,4-tetrahydro-4a-methyl-4aH-carbazole with dimethyl acetylenedicarboxylate: a re-examination. Crystal structures of dimethyl 2a,3,4,5,5a,10-hexahydro-10-[(E)-1,2-bismethoxycarbonylvinyl]-5a-methylcyclobuta[j]carbazole-1,2-dicarboxylate and dimethyl 1,2,3,3a,4,5,12b,12c-octahydro-12c-methoxy-4-methoxycarbonylmethylene-12b-methyl-5-oxazepino[3,2,1-jk]carbazole-6,7-dicarboxylate

Reaction of 1,2,3,4-tetrahydro-4a-methyl-4aH-carbazole with dimethyl acetylenedicarboxylate produces several products, two of which have been characterised by X-ray crystallographic analysis and shown to have the structures dimethyl 2a,3,4,5,5a,10-hexahydro-10-[(E)-1,2-bismethoxy-carbonylvinyl]-5a-methylcyclobuta[j]carbazole-1,2-dicarboxylate, 6 and dimethyl 1,2,3,3a,4,5,- 2b,12c-octahydro-12c-methoxy-4-methoxycarbonylmethylene-12b-methyl-5-oxazepino[3,2,1-jk]-carbazole-6,7-dicarboxylate, 7.