Optimization of an asymmetric version of the reaction promoted by thiourea 48^a.

Entry	Solvent	BzX	M (mol L−1)	(X mol%)	Yield [%]	ee [%]
1	CH2Cl2	BzCl	0.015	20 mol%	79	51
2	Toluene	BzCl	0.015	20 mol%	52	64
3	Toluene	BzBr	0.015	20 mol%	75	83
4	Toluene	BzBr	0.015	10 mol%	83	83
5	Toluene	BzBr	0.020	10 mol%	83	78
6	Toluene	BzBr	0.010	10 mol%	85	84

^aFinal reactions were performed with 19 (0.09 mmol) under argon.