Dearomatization of Aromatic Carbonyl Compounds by Photocycloaddition Reactions to 1,1-Dimethylallene.

The photocycloaddition of 1,1-dimethylallene to various aromatic carbonyl compounds was found to occur exclusively at the benzene core. While the reaction with methyl 2-methoxybenzoate resulted in a mixture of products resulting from ortho, meta, and para photocycloaddition, acetophenone and its 4-substituted derivatives delivered the respective para photocycloaddition products in 50-58% yields. For 2-methoxyacetophenone, an ortho photocycloaddition initiated a reaction cascade, which led to bicyclic products by the incorporation of a nucleophile in 29-74% yields.