2-Methyl-3H-indoles A cyclize with two equivalents of ethyl malonate to 4-hydroxy-11H-benzo[b]pyrano[3,2-f]indolizin-2,5-diones B, whereas 2-methyl-2,3-dihydro-1H-indoles C give under similar conditions regioisomer 8-hydroxy-5-methyl-4,5-dihydro-pyrrolo[3,2,1-ij]pyrano[3,2-c]quinolin-7,10-diones D. The pyrone rings of C and E can be cleaved either by by alkaline hydrolysis to give 7-acetyl-8-hydroxy-10H-pyrido[1,2-a]indol-6-ones or 5-acetyl-6-hydroxy-2-methyl-1,2-dihydro-4H-pyrrolo[3,2,1-ij]quinolin-4-ones, respectively. Chlorination of the pyrones with sulfurylchloride gives under subsequent ringopening 7-dichloroacetyl-8-hydroxy-10H-pyrido[1,2-a]indol-6-ones or 5-dichloracetyl-6-hydroxy-2-methyl-1,2-dihydro-4H-pyrrolo[3,2,1-ij]quinolin-4-ones . The dichloroacetyl group can be reduced with zinc to 7-acetyl-8-hydroxy-10H-pyrido[1,2-a]indol-6-ones . Treatment of the acetyl compounds with 90% sulfuric acid cleaves the acetyl group and yields 8-hydroxy-10H-pyrido[1,2-a]indol-6-ones, and 6-hydroxy-2-methyl-1,2-dihydro-4H-pyrrolo[3,2,1-ij]quinolin-4-ones . Reaction of dichloroacetyl compounds with sodium azide yields 6-hydroxy-2-methyl-5-(1H-tetrazol-5-ylcarbonyl)-1,2-dihydro-4H-pyrrolo[3,2,1-ij]quinolin-4-ones via intermediate geminal diazides.
Reprint as pdf-file on request