Nickel-Catalyzed Stille Cross Coupling of C–O Electrophiles

Aryl sulfamates,
tosylates, and mesylates undergo efficient Ni-catalyzed
cross coupling with diverse organostannanes in the presence of relatively
unhindered alkylphosphine ligands and KF. The coupling is valuable
for difficult bond constructions, such as arylheteroaryl,
arylalkenyl, and arylalkynyl, using nontriflate phenol
derivatives. A combination of experimental and computational studies
implicates an unusual mechanism for transmetalation involving an 8-centered
cyclic transition state. This reaction is inhibited by chloride sources
due to slow transmetalation of organostannanes at a Ni­(II)chloride
intermediate. These studies help to explain why prior efforts to achieve
Ni-catalyzed Stille coupling of phenol derivatives were unsuccessful.