Optimization of reaction conditions^a.

Entry	MgX2 (equiv.)	Temp [°C]	Conv.b [%]	Yieldb [%]
				2a	2a′
1	MgI2 (1.5)	80	60	38	1
2	MgI2 (2)	80	62	40	2
3	MgI2 (3)	80	73	68	4
4	MgI2 (3)	100	>99	93c	6
5	MgBr2 (3)	100	99	93d	5
6	MgCl2 (3)	100	94	89	4

^aAll the reactions were conducted using 0.5 mmol of 1a in THF (2.5 mL).

^bGC yields with n-dodecane as an internal standard.

^cIsolated yield was 96% as a 94 : 6 trans/cis-mixture.

^dIsolated yield was 93% as a 94 : 6 trans/cis-mixture.