Table 1.

Screen of thioureas catalysts with Boc imine 14a.^a

entry	catalyst	Et3N (equiv)	% conversion b	% ee c
1	(1S,2S)-1	0.4	100	8
2	(R)-5	—	0	—
3	(R)-5	0.4	50	4
4	(R)-6	—	65	5
5	(R)-7	0.4	100	5
6	(R)-8	0.4	10	4
7	(R)-9	0.4	36	0
8	(R)-10	0.4	100	16
9	(R)-11	0.4	73	<5
10	(R)-12	0.4	100	74
11	(R,R)-13	0.4	100	6

^aReactions conducted with 10 equiv CH₃NO₂ and 20 mol % catalyst in toluene at 25 °C for 12 h except entry 10 which was 2 h.

^bDetermined by ¹H NMR spectrum of crude reaction mixture.

^cDetermined by HPLC on Chiralpak OJ-H column.