Regioselectivity in the Stille coupling reactions of 3,5-dibromo-2-pyrone.
The Stille couplings of 3,5-dibromo-2-pyrone normally take place regioselectively at C3, lower in electron density than C5, thus oxidative addition proceeds faster . When the reactions are carried out with Cu(I) in DMF or other polar aprotic solvent, however, the couplings occur predominantly at C5. The observed regiochemical reversal is attributed to the preferred formation of 5-pallado-2-pyrone intermediate which, in addition, turned out to be more reactive than 3-pallado-2-pyrone intermediate.
Kim
Won-Suk
WS
Department of Chemistry, Hanyang University, Seoul 133-791, Korea.
Kim
Hyung-Jin
HJ
Cho
Cheon-Gyu
CG