Table 1.

Screening of the catalysts and optimization of the reaction conditions^[a]

Entry	Catalyst	Acid	Solvent	Time [d]	Yield [%][b]	ee [%][c]
1	1	HCl	THF	5	64	66
2	2	HCl	THF	5	63	50
3	3	HCl	THF	5	51	57[d]
4	4	HCl	THF	8	21	40[d]
5	5	HCl	THF	9	trace	nd[e]
6	6	HCl	THF	5	21	5
7	7	HCl	THF	6	56	3
8	1	HCl	dioxane	7	80	61
9	1	HCl	CHCl3	5	60	59
10	1	HCl	CH2Cl2	5	62	50
11	1	HCl	toluene	9	12	37
12	1	HCl	TFE[f]	5	trace	nd[e]
13	1	HCl	CH3CN	5	85	40
14	1	HCl	DMSO	5	83	17
15	1	HCl	acetone	5	43	46
16	1	PhCO2H	THF	15	<5	nd
17	1	2-NBA[g]	THF	15	13	0
18	1	TFA	THF	5	60	44
19	1	p-TSA	THF	8	75	55
20	1	CF3SO3H	THF	6	71	20
21[h]	1	HCl	THF	7	51	52
22[i]	1	HCl	THF	5	73	61
23[i,j]	1	HCl	THF	5	91	62
24[i,k]	1	HCl	THF	5	97	64
25[i,k,l]	1 [m]	HCl	THF	6	81	73
26[i,k,l]	1[n,o]	HCl	THF	6	76	72

^[a]Unless otherwise noted, all reactions were conducted with compounds 8a (0.25 mmol), 9 (0.25 mmol), and 10 (0.25 mmol) in the presence of the catalyst (0.025 mmol, 10 mol %) and the acid cocatalyst (0.025 mmol, 10 mol %) in the specified solvent (1.5 mL) at room temperature.

^[b]Yield of the isolated product after column chromatography.

^[c]Determined by the HPLC analysis on a ChiralCel OD-H column.

^[d]The S-enantiomer was obtained as the major product.

^[e]Not determined.

^[f]2,2,2-Trifluoroethanol.

^[g]2-Nitrobenzoic acid.

^[h]Conducted with 5 mol % of the catalyst and 5 mol % of the acid cocatalyst.

^[i]Conducted with 20 mol % of the catalyst and 20 mol % of the acid cocatalyst.

^[j]Conducted with compounds 8a (0.25 mmol), 9 (0.375 mmol), and 10 (0.75 mmol).

^[k]Conducted with compounds 8a (0.25 mmol), 9 (0.50 mmol), and 10 (1.25 mmol).

^[l]The reaction temperature was 0 °C.

^[m]Catalyst 1 was recovered in 93% yield after the reaction.

^[n]Carried out with the recovered catalyst 1.

^[o]Catalyst 1 was recovered in 98% yield after the reaction.