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‐spiro[4.5]dec‐3‐ene‐3,4‐dicarboxylate ( 6 ) was refluxed in toluene, the previously known dimethyl 4,5,6,7‐tetra‐hydro‐1‐methyl‐1 H ‐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‐1 H ‐indole‐2,3‐dicarboxylate ( 8 ).