Thermal Valence Rearrangements of Heterocycles. Part 2. A new synthetic approach towards the indole ring system

A new synthetic approach towards the indole ring system is described. When dimethyl 1-methyl-2-oxa-1-aza-spiro4.5]dec-3-ene-3,4-dicarboxylate ( 6 ) was refluxed in toluene, the previously known dimethyl 4,5,6,7-tetra-hydro-1-methyl-1H-indole-2,3-dicarboxylate ( 7 ) was obtained in 71% yield, via a 2,3-dihydroisoxazole-pyrrole rearrangement. After treatment with DDQ , the tetrahydro analogue 7 was converted to the corresponding dimethyl 1-methyl-1H-indole-2,3-dicarboxylate ( 8 ).