”Copper Effect” in Migita–Kosugi–Stille Coupling Revisited

”Copper effect” in Migita–Kosugi–Stille coupling (MKSC) has been well known as acceleration effect by a copper cocatalyst, which has thus far been ascribed to two different actions of copper depending on polarity of solvents, i.e., Sn/Cu transmetalation (in polar solvent such as DMF and NMP) and scavenging of ligands (in less polar ethereal solvent). Herein, we report on reconsideration of the copper effect; MKSC is markedly accelerated based on the Sn/Cu transmetalation in ethereal solvents. In particular, perfluorophenyl- and heteroaryl-stannanes were found to undergo the Sn/Cu transmetalation with excellent site-selectivity in the presence of other Ar–Sn bonds under the ethereal conditions, leading to highly chemoselective, sequential MKSC without masking/unmasking process on a tin center. Moreover, we have also demonstrated that a combination of 119Sn NMR chemical shifts (experimental) and computed FIA (theoretical) provides a quantitative criterion estimating tin-Lewis acidity that is strongly linked to activity toward the present MKSC.