2,4,6-Trimethylaniline → 2H-Indol-2-one, 1,3-dihydro-1,6-dimethyl-

Participants

Reaction Conditions

Reaction Steps

A solution of 2,4,6-trimethylaniline (6.86 g, 5 mmol) in dry THF (100 mL) under an atmosphere of N2 was cooled to -78° C. and n-butyllithium (21 mL, 2.5M solution in hexanes) was added dropwise. The mixture was allowed to warm to 0° C., and dry CO2 gas was bubbled in for 2-3 minutes. The excess CO2 was removed under vacuum, and after the addition of further THF to replace that lost by evaporation, the solution was recooled to -78° C. n-Butyllithium (22 mL, 2.5M solution in hexanes) was again added dropwise, and the temperature was then allowed to rise slowly to -10° C. where a deep red colored solution was obtained. After a further 30 minutes at that temperature, the mixture was again recooled to -78° C. and CO2 gas was bubbled in until the red color disappeared. The reaction mixture was allowed to warm to 20° C., and after removal of the solvent, 0.1M HCL (50 mL) was added to initiate both deprotection of the nitrogen and ring-closure. The resulting mixture was extracted with EtOAc, and this was then washed successively with 0.1M HCl, water, and dilute aqueous Na2CO3. After drying (Na2SO4), the solvent was removed under vacuum, to leave an oil which was purified by chromatography on Al2O3 to give 1,6-dimethyl-2-indolinone (3.37 g, 42% yield) [VII: R1 =6-Me; R3 =Me]; mp (hexane) 94.5°-96° C.

Provenance & Evidence