Table 2. Screening of the Model Reaction in Various Solvents^a.

entry	solvent	yield (%)
1	DMF	94
2	EtOH	–
3	DCE	73
4	ACN	86

^aReaction conditions: 1a (0.1 mmol), 2 (0.1 mmol), 3 (0.25 mmol), 4 (0.35 mmol), Sc(OTf)₃ (20 mol %), dry solvent (2 mL) 70 °C, N₂ atmosphere. DMF = N,N-dimethylformamide. DCE = 1,2-dichloroethane. ACN = acetonitrile. It is noteworthy that the presence of solid potassium carbonate as a base in dry pyridine did not affect the global yield when the reaction was performed at a gram scale (Table 1, entry 9). Finally, the reaction performed equally well with ScBr₃ as a catalyst (Table 1, entry 10). Using the optimized conditions [20% Sc(OTf)₃], the protocol was extended to substrates 1b–l, starting from commercially available isatins subjected to N-alkylation²⁹ (Table 3).