Table 1. Screening of catalysts and oxidants for the enantioselective coupling of aldehyde 1a to indole 2a ^a .

Entry	Cat.	Oxidant	Temp. (°C)	Yield (%)	ee (%)
1 b	3a	CAN	RT	0	—
2 b	3a	CAN	–20	0	—
3 b	3a	Cu(OTf)2	–20	0	—
4 c	3b	DDQ	RT	38	—
5 c	3c	DDQ	RT	0	—
6 c	3d	DDQ	RT	41	66
7	3d	DDQ	RT	70	70
8	3d	Fluoranil	RT	31	63
9	3d	Chloranil	RT	10	43
10	3e	DDQ	RT	63	58
11	3f	DDQ	RT	64	82
12 d	3f	DDQ	RT	73	94

^aPerformed on a 0.10 mmol scale under Ar: 1.0 equiv. 1a, 5.0 equiv. 2a, 0.20 equiv. 3, 1.5 equiv. acid, 1.1 equiv. oxidant and 0.4 mL CH₂Cl₂.

^b2.0 equiv. oxidant and 0.4 mL DME.

^cAcid omitted.

^dDDQ added in two portions.