Photochemical Isomerization of Cyclohept-1-ene-1-carbaldehyde: Strain-Release Cycloadditions and Ene Reactions.

Cyclohept-1-ene-1-carbaldehyde undergoes photoinduced → isomerization at λ = 350 nm. The ring strain facilitates Diels-Alder cycloaddiions with 1,3-dienes, [3 + 2] cycloadditions with 1,3-dipoles, and ene reactions with olefins. Products are -fused at the cycloheptane core and were obtained in yields of up to 82%. Single crystal X-ray analyses corroborated the constitution and relative configuration of key products. With BF as a Lewis acid and 2,3-dimethylbuta-1,3-diene, cyclohept-1-ene-1-carbaldehyde reacted in the dark and rearranged stereoselectively to a tricyclic ketone (87%).