Table 1. Cyclization of 4-pentynoic acid (1) ^a .

Entry	Conditions a	Yield b (%)
1	XantphosCu(i)	12
2	XantphosCu(ii)	4
3	CuOAc	2
4	Cu(OAc)2	0
5 c	XantphosCu(i) + Et3N	39
6 c	XantphosCu(ii) + Et3N	17
7 c	CuOAc + Et3N	11
8 c	Cu(OAc)2 + Et3N	0

^aReaction conditions: [1] = 10 mM, [Cu] = 0.5 mM, CD₃CN, RT, 24 h.

^bYield determined by ¹H NMR spectroscopy using 1,3,5-trimethoxybenzene as an internal standard.

^c[Et₃N] = 1.5 mM.