Table 2. Control experiments of β-lactam formation.

Entry	Change from the ‘standard conditions’*	Yield of 2d (%)†
1	None	88
2	No Co(OAc)2	0
3	Shi’s conditions‡ instead of the standard conditions	0
4	Co(OAc)2 (1 eq), no Ag2CO3	0
5	Ce(SO4)2 (6 eq) instead of Ag2CO3	25
6	Co(acac)3 (1 eq) instead of Co(OAc)2, no Ag2CO3	0
7	CoF3 (1 eq) instead of Co(OAc)2, no Ag2CO3	0
8	Co(acac)3 (10%) instead of Co(OAc)2	53
9	CoF3 (10%) instead of Co(OAc)2	46
10	Addition of TEMPO (1 eq)	63
11	Addition of TEMPO (2 eq)	56

^*Reaction conditions: 1d (0.3 mmol), Co(OAc)₂ (0.03 mmol), Ag₂CO₃ (0.75 mmol), PhCO₂Na (0.15 mmol), 0.6 ml PhCl, 150 °C, 24 h.

^†Yields are based on 1d, determined by ¹H NMR using dibromomethane as the internal standard.

^‡Shi’s conditions: 1d (0.25 mmol), AgOAc (20 mol%), PhI(TFA)₂ (0.50 mmol), 4,4′-di-t-butyl-2,2′-bipyridine (20 mol%), K₂CO₃ (0.50 mmol), PhCl/DCE (1.5 ml/1.5 ml), 120 °C, 12 h.