Optimization studies for the synthesis of indoles^a.

Entry	Deviation from the standard conditions	Yieldb/%
1	None	82
2	Other solvents instead of the mixed solvents	<70
3c	B2(OH)4 instead of B2nep2	62
4	Other diboron reagents instead of B2(OH)4 or B2nep2	<30
5	0.5 equiv. instead of 2.2 equiv. B2nep2	35
6	1.0 equiv. instead of 2.2 equiv. B2nep2	52
7	Other catalytic bases instead of DIPEA	<60
8	Without DIPEA	40
9	Without B2nep2	Trace
10	In the dark	0
11	In air	48

^aStandard reaction conditions: 1a (0.2 mmol), DIPEA (0.04 mmol), B₂nep₂ (0.44 mol), THF/MeOH (8/1, 0.45 mL), N₂, rt, under the irradiation of blue LEDs (400 nm), 12 h.

^bIsolated yields of 2a.

^cB₂(OH)₄: tetrahydroxydiboron; B₂nep₂: bis(neopentylglycolato)diboron.