Screening of solvents^a.

Entry	Solvent	Time	Yieldb (%)	eec (%)
1	n-Hexane	24	52	48
2	Toluene	72	49	45
3	CH2Cl2	72	41	30
4	EtOAc	24	67	54
5	CH3OCH2CH2OCH3	36	47	40
7	MTBE	36	84	49
8	THF	36	81	69
9	Dioxane	36	76	57
10	MeOH	24	69	57
11	Ethylene glycol	24	42	57

^aReaction conditions: the azodicarboxylate (1 equiv.) was added to the aldehyde (1.5 equiv.), with catalyst (15 mol%) in THF at rt for the stated period of time under argon. Reaction without isolation of intermediate.

^bIsolated yield.

^cDetermined by chiral HPLC.