Influence of the catalyst structure.

Entry	Cat.	X (mol%)	Solvent	Time (d)	Yielda (%)	syn : antib	eec (%)
1d	DABCO	20	DCM	2	45	1 : 1.2	—
2	3a	20	Toluene	4	80	5.4 : 1	88
3e	3a	20	Toluene	7	76	7.0 : 1	93
4	4a	20	Toluene	4	80	1 : 11	56
5f	4a	5	DCE	2	95	1 : 24	70
6f	4b	5	DCE	2	90	1 : 15	95
7	8	20	Toluene	4	52	3.9 : 1	72
8	9	20	Toluene	4	51	3.5 : 1	73
9	6a	20	Toluene	4	33	1.6 : 1	56
10	10	20	Toluene	4	79	1 : 5.2	63
11	11	20	Toluene	1	89	1 : 3.0	61
12	12	20	Toluene	1	63	1.2 : 1	84

^aIsolated yield.

^bDetermined by ¹H NMR analysis of the crude mixture.

^cDetermined by HPLC analysis.

^dRoom temperature.

^e0.3 mmol, with 90 mg powdered 5 Å MS, [1a] = 0.3 M.

^f[1a] = 0.1 M. [1a] = 0.2 M without noted. DCM: CH₂Cl_2. DCE : CH₂ClCH₂Cl.