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

Cyclohept-1-ene-1-carbaldehyde undergoes photoinduced E → Z 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 trans-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 BF3 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%).