Harnessing sunlight without a photosensitizer for highly efficient consecutive [3+2]/[4+2] annulation to synthesize fused benzobicyclic skeletons.

A photosensitizer-free, highly efficient sunlight-promoted tandem [3+2]/[4+2] annulation of unsaturated α-bromocarbonyls with o-alkynylanilines was developed, and allowed for convenient synthesis of fused benzobicyclic skeletons. The reaction was clean and practical in mild conditions and showed excellent functional group compatibility.