Table 1. Optimisation of reaction parameters.

Entry a	Solvent	Additive [mol%]	T [°C]	Cat. loading [mol %]	Yield b [%]
1	DCE	PhCO2 Na (40)	80	10	16
2	Toluene	PhCO2 Na (40)	80	10	0
3	Dioxane	PhCO2 Na (40)	80	10	Trace
4	CHCI3	PhCO2 Na (40)	80	10	Trace
5	DCE	AdCO2 Na (40)	80	10	23
6	DCE	PivCO2 Na (40)	80	10	18
7	DCE	Amino acid (40)	80	10	Scheme 2
8	DCE	Fmoc-Pro-ONa (40)	80	10	55
9	DCE	Fmoc-Pro-ONa (30)	80	10	62
10	DCE	Fmoc-Pro-ONa (20)	80	10	57
11	DCE	Fmoc-Pro-OK (30)	80	10	0
12	DCE	Fmoc-Pro-OLi (30)	80	10	0
13	DCE	Fmoc-Pro-OAg (30)	80	10	0
14	DCE	Fmoc-Pro-ONa (30)	70	10	45
15	DCE	Fmoc-Pro-ONa (30)	90	10	47
16	DCE	Fmoc-Pro-ONa (30)	80	15	73(71)

^aReaction conditions: 1a (0.05 mmol), 2a (0.1 mmol), catalyst, additive, solvent (0.5 mL), temperature, 36 h.

^bYield calculated by ¹H NMR with methyl para-nitrobenzoate as internal standard; isolated yield of product in parentheses.