Table 1. Diastereoselective azo-coupling of tryptophan derivatives ^a .

Entry	Solvent	T (°C)	Reaction time	15 : 16	Yield b (%)
1	MeOH	–78	1 h	1 : 1	66%
2	MeCN	rt	24 h	—	— c
3	Toluene	rt	24 h	1 : 1.5	41%
4	THF	rt	24 h	1 : 1.5	74%
5	THF	15	24 h	Only 16	14%
6	DCE	15	24 h	1 : 5	82%
7	DCE	rt	24 h	1 : 5	57%
8	DCE–THF(1 : 1)	15	48 h	1 : 10	63%
9	DCE–THF(1.5 : 1)	15	48 h	<1 : 25	67% (61 d %)
10	DCE–THF(2 : 1)	15	96 h	1 : 20	50%
11	DCE–THF(4 : 1)	15	96 h	1 : 4	43%

^aConditions: 14 (0.1 mmol), PhN₂BF₄ (0.11 mmol), K₂CO₃ (0.15 mmol) and solvent (1 mL).

^bNMR yield with 1,3,5-trimethoxylbenzene as internal standard.

^cNo desired product was detected.

^dIsolated yield.