Optimization study of reaction conditions^a.

Entry	Variation from standard condition	Yield (%)b	trans : cisb
1	None	98 (93)c	89 : 11
2	25 °C, 24 h	81	90 : 10
3	1b (2 equiv.) instead of 1a	0	N/A
4	1c (2 equiv.) instead of 1a	0	N/A
5	1d (2 equiv.) instead of 1a	0	N/A
6	TDAE (2 equiv.) instead of 1a	0	N/A
7	Zn (6 equiv.) instead of 1a	0	N/A
8	Mn (6 equiv.) instead of 1a	0	N/A
9	Addition of ZnCl2 (2 equiv.)	0	N/A
10	Addition of MnCl2 (2 equiv.)	56	87 : 13
11	Without TMEDA	7	71 : 29
12	L1 (5 mol%) instead of TMEDA	97	90 : 10
13	L2 (5 mol%) instead of TMEDA	7	57 : 43
14	L3 (5 mol%) instead of TMEDA	0	N/A
15	L4 (5 mol%) instead of TMEDA	8	>99 : 1
16	L5 (5 mol%) instead of TMEDA	0	N/A
17	L6 (5 mol%) instead of TMEDA	0	N/A
18	CrCl3(tmeda) (5 mol%) instead of CrCl3(thf)3 and TMEDA	90	88 : 12

^aReaction condition: 2a (0.1 mmol), bromoform (2 equiv.), CrCl₃(thf)₃ (5 mol%), ligand (5 mol%), and reductant (above-mentioned amount) in 1,2-dimethoxyethane (DME, 0.10 M) at 50 °C for 24 hours.

^bDetermined by ¹H NMR analysis using 1,3,5-trimethoxybenzene as an internal standard.

^cIsolated yield. TDAE: tetrakis(dimethylamino)ethylene.