Construction of cyclopentane-fused coumarins via DBU-catalyzed [3+2] cycloaddition of 3-homoacyl coumarins with cyclic 1-azadienes.

The metal-free DBU catalyzed [3+2] cycloaddition of 3-homoacyl coumarins with cyclic 1-azadienes proceeded smoothly to furnish the corresponding highly functionalized cyclopentane-fused coumarins with excellent diastereoselectivity and complete chemoselectivity and in good yields under mild conditions.