E. Ciganek et Em. Schubert, INTRAMOLECULAR DIELS-ALDER REACTIONS .5. APPROACHES TO THE PYRROLO[3,4-C] CARBAZOLE AND PYRIDO[4,3-C] CARBAZOLE SYSTEMS, Journal of organic chemistry, 60(14), 1995, pp. 4629-4634
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.