INTRAMOLECULAR DIELS-ALDER REACTIONS .5. APPROACHES TO THE PYRROLO[3,4-C] CARBAZOLE AND PYRIDO[4,3-C] CARBAZOLE SYSTEMS

Two methods for the preparation of indole-2,3-quinodimethanes are repo rted. Treatment of -(phenylmethyl)-N-2-propenyl-1H-indole-3-acetamide (3) with sodium bis(trimethylsilyl)amide in refluxing THF gave 5,6,10c -hexahydropyrrolo[3,4-c]-carbazol-1(2H)-one (5) in 18% yield by intram olecular Diels-Alder reaction of the intermediate enolate 4. LiBH4-red uction of amide 3 and thermolysis of the resulting alpha-hydroxyamide 8 at 190 degrees C gave a 63:37 mixture of the cis and trans isomers o f ,5,6,10c-hexahydropyrrolo[3,4-c]carbaxol-1(2H)-one (9a and 9b) in 64 % yield. The corresponding N-3-butenylamide 10 at 205 degrees C led to a 67:33 mixture of cis- and ro-2-(phenylmethyl)-1H-pyrido[4,3-c]carba zol-1-one (11a and 11b) in 53% yield. Thermolysis of -(phenylmethyl)-N -2-propynyl-1H-indole-3-acetamide (15) gave an equimolar mixture of la ctam 9a and the aromatized product, l-2-(phenylmethyl)pyrrolo[3,4-c]ca rbazol-1(2H)-one (17) in 80% yield by disproportionation of the interm ediate lactam 16. Reaction of 1,2-dimethyl-1H-indole-3-carboxaldehyde with methyl acrylate and sodium bis(trimethylsilyl)amide produced meth yl 1,2-dihydro-9-methyl-9H-carbazole-3-carboxylate (20) in 26% yield, most likely by a sequence of Michael addition to the enolate of the al dehyde and intramolecular aldol condensation.