Controllable Dearomative Photocycloaddition of Triplet Benzenes With Allenes.

A divergent visible light-induced photocycloaddition (PCA) of benzene derivatives with allenes is described, enabled by efficient sensitization of simple arene moieties using an iridium triplet sensitizer. The reactions, governed by the tethered allene chain, proceed selectively through two distinct pathways: para- and ortho-cycloaddition. The para-cycloaddition pathway, influenced by substituent effect, can further deliver a range of formal meta-type products following a subsequent di-π-methane rearrangement. In comparison, the ortho-cycloaddition pathway produces linear tricyclic cyclobutenes via cascade electrocyclic reactions. Modulated by the substituent on the allene moiety, a sequential di-π-methane rearrangement furnishes different formal meta-type products. Control experiments, together with density functional theory (DFT) calculations, provide a comprehensive understanding of the underlying reaction pathways.