Table 1.

Base Screen^a

entry	base	yield (%)b	drc	ee (%)d
1	Et3N	39	9:1	14
2e	Et3N	trace	---	---
3	KHMDS	25	5/1	23
4	NaOAc	62	5/1	42
5	PhCOONa	72	6/1	50
6	A1	94	5/1	57
7	A2	94	5/1	59
8	A3	76	6/1	33
9	A4	80	6/1	41

^aConditions: 2a, 0.2 mmol; 1a, 0.1 mmol; base, 20 mol%; C1 (structure in Table 2), 20 mol%; CH₂Cl₂, 1 mL; 4A MS under Ar.

^bNMR yields of trans and cis-diastereomers (internal standard).

^cThe ratio of trans/cis determined by ¹H NMR.

^dEe of trans-3a determined by chiral HPLC.

^e1.2 eq of Et₃N was used.