Table 2. Effect of Et₃N^a,b.

entry	catalyst (mol%)	additive (mol%)	yield (%)	ee (%)
1	2 (10)	none	70	88
2	2·HCl (10)	none	21	18
3	2·HCl (10)	Et3N (50)	76	84
4	2 (10)	Et3N (50)	95	99
5	2 (10)	Et3N (25)	96	99
6	2 (5)	Et3N (25)	83	94
7c	2 (10)	Et3N (50)	70	93

^aConditions: substrate (0.05 mmol), catalyst (10 mol%), diketone (0.1 mmol), DCM (1 mL), under N₂, initially cooled to −78 °C and stirred at −0 °C, 36 h.

^bThe yield was determined by the ¹H NMR analysis of the crude product using CH₂Br₂ as the internal standard.

^cReaction carried out in the absence of added 4 Å MS.