The effect of reaction temperature.

Entrya	Temp. (°C)	Time (h)	Yieldb (%)	eec (%)
1	20	36	78	91
2	0	36	78	93
3	−20	36	68	95
4	−20	48	76	95
5	−50	72	78	98
6	−55	72	78	99
7	−60	72	77	98
8d	−55	72	78	99
9e	−55	72	75	99

^aConditions: 1a (0.1 M), ClCOOBn (3.5 eq.), OBn-DPI (20 mol%), DIPEA (4.0 eq.), toluene (2 mL), unless otherwise noted.

^bYields were calculated from ¹H NMR spectra.

^cThe ee values were calculated from HPLC spectra.

^dClCOOBn (3.0 eq.).

^eClCOOBn (2.5 eq.).