Isomeric solid enols on ring- and amide-carbonyls of substituted 2-carbanilido-1,3-indandiones

Both isomeric enols on ring carbonyl (5b) and on amide carbonyl (6b) derived from N-p-methoxyphenyl-2-carbamido-1,3-indandione (4b) were isolated, and their X-ray structures were determined. X-ray diffraction of the N-o,p-dimethoxy analogue indicated a disorder ascribed to the presence of a 6:4 mixture of 5c and 6c. Calculation (B3LYP/6-31+G*) gave good agreement with observed geometries. The calculated energies indicated that enols 6 are more stable by <1 kcal/mol than enols 5 and much more stable than amides 4.