Table 1.

Thiourea catalyst optimization

entry	thiourea catalyst	T (°C)a	[1a]o (M)	yield[%]b	ee[%]c
1	-	−78	0.1	0	N/A
2	4	−78	0.1	75	10
3	5a	−78	0.1	68	50
4	5b	−78	0.1	63	20
5	5c	−78	0.1	57	80
6	5d	−78	0.1	63	29
7	5c	−60	0.05	37	93
8	epi-5c d	−60	0.05	68	44
9	5e	−60	0.05	63	87
10	5f	−60	0.05	63	85
11	ent-5g	−60	0.05	72	−97

^aReaction temperature for the alkylation step in MTBE.

^bYields determined by ¹H NMR spectroscopic analysis of the crude reaction mixture relative to 2,5-dimethylfuran as the internal standard.

^cDetermined by HPLC on commercial chiral columns.

^dPyrrolodine configuration is (R), tert-leucine configuration is (S).