Merging [2 + 2] Cycloaddition with 1,6-/1,4-Aza-Binucleophilic Additions toward Unprecedented Indazole-Containing Polycycles

Bu-Zheng Tang, Jia-Zhuo Li, Ai-Wen Zhang, Wen-Juan Hao,* Shu-Jiang Tu, Bo Jiang*

The first metal-free [2 + 2] cycloaddition and 1,6-/1,4-aza-binucleophilic addition cascade of yne-allenone esters and cyclic aza-binucleophiles was reported, leading to the atom-economic protocol toward hitherto unreported indazole-containing polycycles with one quaternary carbon-amino functionality and good to excellent yields. The reaction pathway involves [2 + 2] cycloaddition, ring-opening of fused cyclobutenes and 1,6-/1,4-aza-binucleophilic addition sequence, resulting in continuous multiple bond-forming events including C–C and C–N bonds to build up molecular complexity.

Adv. Synth. Catal. 2019, 361, 3394-3402