1,4-Diazabicyclo[2.2.2]octane (DABCO)-Catalyzed [4+2] Domino Reaction of Allenoates: Synthesis of Benzo[4,5]thieno-[3,2-b]pyran Derivatives

A 1,4-diazabicyclo[2.2.2]octane (DABCO)-catalyzed [4+2] annulation reaction between 2-alkylidenebenzothio phene-3(2H)-ones and allenoate has been developed. The substrate scope includes both electron-withdrawing and electron-donating groups on the benzothiophene moiety. This method can be carried out under mild conditions and gives a wide range of highly functionalized benzothiophene-fused gamma-pyran derivatives in good yields with moderate selectivity.