Optimization of the reaction conditions^a.

Entry	Base	Solvent (v/v)	Yieldb (%)
1	K2CO3	TCE : H2O = 7 : 2	38
2	NaOH	TCE : H2O = 7 : 2	37
3	KOtBu	TCE : H2O = 7 : 2	31
4	Piperidine	TCE : H2O = 7 : 2	57
5	DMAP	TCE : H2O = 7 : 2	40
6	Morpholine	TCE : H2O = 7 : 2	35
7	PDA	TCE : H2O = 7 : 2	58
8	4-ADPA	TCE : H2O = 7 : 2	75
9		TCE : H2O = 7 : 2	30
10	4-ADPA	TCE : H2O = 5 : 4	48
11	4-ADPA	TCE : H2O = 2 : 7	35
12	4-ADPA	DMSO : H2O = 7 : 2	22
13	4-ADPA	Anisole : H2O = 7 : 2	43
14	4-ADPA	PhCl : H2O = 7 : 2	29
15c	4-ADPA	TCE : H2O = 7 : 2	61
16d	4-ADPA	TCE : H2O = 7 : 2	52

^aConditions: 1a (0.2 mmol), 2a (0.5 mmol), base (0.2 mmol), paraformaldehyde (0.8 mmol), solvent (0.9 mL), 130 °C, 3 h, air. PDA = 1,4-benzenediamine, 4-ADPA = 4-aminodiphenylamine, TCE = 1,1,1,2-tetrachloroethane.

^bGC yields.

^c110 °C.

^d4-ADPA (0.1 mmol).