Table 1.

Optimizations of reaction conditions^a.

Entry	R	Catalyst	Solvents	Yieldb (%)	drb (3a:4a)	eec (3a/4a, %)
1	PMP	A1	toluene	52	1:2.8	45/31
2	PMP	A2	toluene	41	1:1	41/24
3	PMP	A3	toluene	51	1.4:1	35/57
4	PMP	A4	toluene	50	1.3:1	72/81
5	PMP	A5	toluene	68	1:2.5	24/90
6	PMP	B1	toluene	57	2.7:1	91/34
7	PMP	B2	toluene	91	10:1	87/–
8	PMP	C1	toluene	51	1:11	–/98
9	Ar	B2	toluene	99	12:1	91/–
10	Ar	C1	toluene	80	1:9	–/94
11	Ar	B2	CCl4	98	20:1	91/–
12	Ar	C1	CCl4	85	1:12	–/98

^aReactions were performed with 1a (0.15 mmol), 2a (0.1 mmol), cat (0.01 mmol), 3 Å MS (100 mg), solvents (0.5 mL) at ambient temperature for 24 h.

^bYields and dr value were determined by crude ¹H NMR analysis using 1,2-dimethoxyethane (DME, 0.1 mmol) as internal standard.

^cee values were determined by HPLC analysis on a chiral stationary phase. PMP = para-methoxylphenyl, Ar = 3,5-dimethoxyphenyl.