Table 1. Optimisation of the cross-coupling of thiocarbonylthio 5 with boronic acid 4b.

Entry 5		Cu salt	Solvent	Temp	Yield a
1	a	Cu(acac)	THF	66	0
2	′′	CuCl2·H2O	′′	′′	Trace
3	′′	Cu powder	′′	′′	12
4	′′	Cu(OAc)2·H2O	′′	′′	21
5	′′	Cu(BF4)2·H2O	′′	′′	35
6	′′	′′	Dioxane	′′	12
7	′′	′′	DMF	′′	21
8	′′	′′	Toluene	′′	16
9	′′	′′	CH2Cl2	40	42
10	′′	′′	DCE	66	54
11 a	b	′′	DCE	80	67
12 a	b	Cu(BF4)2·H2O·EtOAc	′′	80	85

^aIsolated yields.