Photoreduction to alkenes usually occurs when simple acyclic mono- and di-alkylacetylenes are photolysed at 185 nm in hydrocarbon solvents such as pentane. 1 Intramolecular abstraction of a secondary hydrogen from an alkyl substituent by photoexcited acetylene and cyclization of the resultant diradical has only been observed with cyclononyne, which gives bicyclo[4.3.0]non-l-ene (@ = 0.25) in addition to (E,Z)-cyclononenes (@ = 0.16).1 We ...