Optimization of the reaction conditions^a.

Entry	Catalystk	Solventl	Time (h)	Yieldb (%)
1	DABCO	Toluene	12	NR
2	Pyrrolidine	Toluene	12	Trace
3	NaOAc	Toluene	12	NR
4	DMAP	Toluene	12	NR
5	TMG	Toluene	12	Trace
6	DBU	Toluene	12	48
7	TBD	Toluene	12	22
8	MTBD	Toluene	12	18
9	DBN	Toluene	12	28
10	DBU	DCM	12	28
11	DBU	EA	12	59
12	DBU	MeOH	12	25
13	DBU	MeCN	12	46
14	DBU	THF	12	64
15	DBU	1,4-Dioxane	12	NR
16	DBU	DMSO	12	20
17	DBU	H2O	12	NR
18	DBU	THF	24	82
19c	DBU	THF	24	80
20c,d	DBU	THF	24	79
21e	DBU	THF	24	77
22f	DBU	THF	24	59
23f,g	DBU	THF	12	82
24f,g,h	DBU	THF	12	84
25f,g,i	DBU	THF	12	55
26g,j	DBU	THF	24	24

^aUnless otherwise noted, the reaction was carried out with 1a (0.1 mmol), 2a (0.3 mmol), catalyst (20 mol%), solvent (1.0 mL) at 60 °C.

^bIsolated yields, dr > 20 : 1, dr values were measured by crude HNMR.

^c2a (0.5 mmol).

^d40 °C.

^eAdditive: 4 Å molecular sieve.

^fCatalyst (10 mol%).

^gSolvent (0.5 mL).

^h2a (0.15 mmol).

ⁱ2a (0.1 mmol).

^jCatalyst (5 mol%).

^kDABCO = 1,4-diazabicyclo[2.2.2]octane, DMAP = 4-dimethylamino-pyridine, TMG = 1,1,3,3-tetramethylguanidine, TBD = 1,5,7-triaza-bicyclo[4.4.0]dec-5-ene, MTBD = 7-methyl-1,5,7-triazabi-cyclo[4.4.]dec-5-ene, DBN = 1,5-diazabicyclo[4.3.0]non-5-ene, DBU = 1,8-diazabicyclo-[5.4.0]undec-7-ene.

^lDCM = dichloromethane, EA = ethyl acetate, THF = tetrahydrofuran, DMSO = dimethyl sulfoxide.