Table 1. Catalyst identification and optimization of reaction conditions ^a .

Entry	Catalyst	t [h]	Yield [%] of 3aa b	Yield [%] of 4aa b	er of 4aa c
1 d	None	6	90	90	—
2	None	48	<5	—	—
3	I	48	88	85	94.5 : 5.5
4	II	46	95	87	94 : 6
5	III	48	>99	86	92 : 8
6	IV	48	90	86	92 : 8
7	V	48	90	85	93 : 7
8	VI	48	>99	88	70 : 30
9	VII	24	>99	88	97.5 : 2.5
10 e , f	VII	24	—	48	97.5 : 2.5
11 e , g	VII	24	—	91	97.5 : 2.5

^aReactions were carried out on a 0.1 mmol scale using 1.0 equiv. of 1a and 1.2 equiv. of 2a.

^bYields correspond to the isolated product.

^cThe enantiomeric ratio (er) was determined by HPLC analysis.

^dReaction at 25 °C.

^eUsing 2.0 equiv. of DBU.

^fOne-pot reaction in 2-MeTHF. Time required for the 2nd step was 40 h.

^gOne-pot reaction with solvent switch.