Enantioselective Intramolecular ortho Photocycloaddition Reactions of 2‐Acetonaphthones

2‐Acetonaphthones, which bear an alkenyl group tethered to its C1 carbon atom via an oxygen atom, were found to undergo an enantioselective intramolecular ortho photocycloaddition reaction. A chiral oxazaborolidine Lewis acid leads to a bathochromic absorption shift of the substrate and enables an efficient enantioface differentiation. Visible light irradiation (λ=450 nm) triggers the reaction which is tolerant of various groups at almost any position except carbon atom C8 (16 examples, 53–99 % yield, 80–97 % ee). Consecutive reactions were explored including a sensitized rearrangement to tetrahydrobiphenylenes, which occurred with full retention of configuration. Evidence was collected that the catalytic photocycloaddition occurs via triplet intermediates, and the binding mode of the acetonaphthone to the chiral Lewis acid was elucidated by DFT calculations. The intramolecular ortho photocycloaddition of 2‐acetonaphthones has been achieved with high enantioselectivity. The catalytic use of a chiral Lewis acid was critical for the success of the reaction and its mode of action has been elucidated by mechanistic experiments and calculations. The primary photocycloaddition products underwent photochemically or thermally a variety of consecutive reactions.