Table 1. Reaction optimization. Full optimization data available in the ESI.

Entry	Catalyst	Solvent	Yield a (%)	er b
1 (ref. 14)	A	THF	12	53 : 47
2	B	THF	80	83 : 17
3 c	C	THF	92	86 : 14
4	D	THF	83	66 : 34
5	E	THF	95	83 : 17
6	F	THF	90	90 : 10
7 d	None	THF	95	50 : 50
8 e	F	Et2O	93	94 : 6
9 f	F	Et2O	88	82 : 18
10 e	G	Et 2 O	98	95 : 5

^aIsolated yield.

^bDetermined by HPLC analysis on a chiral stationary phase.

^cReaction carried out at 0.25 M concentration.

^dReaction carried out over 72 h.

^eReaction carried out at 0 °C, using 1.2 eq. of thiol and 0.06 M concentration.

^fReaction carried out at –40 °C, using 1.2 eq. of thiol and 0.06 M concentration.