Deprotonation of furans using lithium magnesates

Furan was deprotonated on treatment with 1/3 equiv of Bu3MgLi in THF at rt. The lithium arylmagnesate formed was either trapped with electrophiles or involved in a palladium-catalyzed cross-coupling reaction with 2-bromopyridine. The highly coordinated magnesate Bu4MgLi2 (1/3 equiv) proved to be a better deprotonating agent than Bu3MgLi; the monitoring of the reaction using NMR spectroscopy showed that the deprotonation of furan at rt required 2 h whereas the subsequent electrophilic trapping was instantaneous. The method was extended to benzofuran, allowing its functionalization at C2 in high yields. The deprotonation of 2-methylfuran and lithium furfurylalkoxide at C5 turned out to be difficult, requiring either long reaction times or higher temperatures.