Table 1. Optimization for the Pd-catalyzed C-2 arylation of 1-methylindole ^a .

Entry	Catalyst (mol%)	Solvent	Reaction time	Yield GC-FID (%)
1	Pd(OAc)2 (10.0)	DMF	30 min	66
2	Pd(OAc)2 (5.0)	DMF	30 min	34
3	—	DMF	16 h	0
4	Pd(OAc)2 (5.0)	Solvent b	30 min	<72
5	Pd(OAc)2 (5.0)	THF	30 min	77; 76 c
6	Catalyst (5.0) d	THF	2 h	0
7	Pd(TFA)2 (5.0)	THF	30 min	76
8	Pd2(dba)3 (2.5)	THF	30 min	68
9	Pd(OAc)2 (0.5)	THF	1 h	81
10	Pd(OAc)2 (0.2)	THF	1 h	Trace
11	Pd(OAc)2 (0.5)	2-MeTHF	2 h	87
12	Pd(OAc)2 (0.5)	EtOAc : 2-MeTHF (1 : 1)	1 h	89
13	Pd(OAc)2 (0.2)	EtOAc : 2-MeTHF (1 : 1)	1 h	78
14 e	Pd(OAc)2 (0.5)	EtOAc : 2-MeTHF (1 : 1)	30 min	93; 90 f

^aReaction conditions: catalyst, 0.5 mmol heteroarene and 1.2 equiv. benzenediazonium tetrafluoroborate in 2.5 mL solvent at rt, 0.1 equiv. decafluorobiphenyl as internal standard for GC-FID, open flask.

^bSolvent: H₂O, AcOH, EtOAc, propylene carbonate, DMF, acetone, MeCN, Et₂O, 1,4-dioxane, MeOH, EtOH, i-PrOH n-BuOH, DCM, DCE, CHCl₃, toluene.

^cSchlenk line techniques used.

^dCatalyst: 10% Pd/C, PdCl₂, Cu(OAc)₂, Cu(OTf)₂, Pd[P(C₆H₅)₃]₄, (MeCN)₂Pd(ii)Cl₂ and (η³–C₃H₅)₂Pd₂Cl₂, PEPPSI-SIPr.

^e2 h premixing of Pd(OAc)₂ with 1-methylindole, 1.0 equiv. of benzenediazonium tetrafluoroborate used.

^fisolated yield.