7-Azaindolium TFPB: Efficient H-Bonding Catalyst

Significance

7-Azaindolium TFPB 3 was found to efficiently activate nitroalkenes 1 towards conjugate addition of electron-rich heteroarenes and arenes (1 example) 2. Excellent yields of products 4 could be obtained with the remarkably low catalyst loading of only 0.5 mol%. In the case of N-methyl indole, 0.05 mol% 3 was sufficient to promote the reaction (see example 5). The present work also includes the first report on Diels-Alder (DA) reactions of nitroalkenes mediated by an H-bonding catalyst. With 20 mol% of catalyst 3, the DA reaction of nitroalkenes 1 with cyclopentadiene gives moderate yields. When compared to acyclic 2-benzylaminopyridinium TFPB 6, the conformationally rigid and fully conjugated catalyst 3 gave improved results regarding yields and selectivity.