Photocyclization of Cyclononene and Cycloundecene

Article abstract of DOI:10.1021/jo00013a041

Irradiation of cyclooctene (7b) and cycloundecene (7d) in pentane afforded cis-bicyclo<4.3.0>nonane (10b) and cis-bicyclo<6.3.0>undecane (10d), respectively.Small amounts of the fragmentation products 1-undecene (14d) and 1-undecyne (15d) were also obtained from cycloundecene (7d).The photobehavior of the series of medium- and large-ring alkenes 7a-e is compared.Aside from E <-> Z isomerization, the principal pathway in each case involves rearrangement of the ?,R(3s) excited state to the cycloalkylidene intermediate 8, which undergoes predominant, if not exclusive, 1,5-transannular insertion to afford the corresponding cis-bicycloalkanes (10).The cycloalkylidene 8 formed in this way exhibit behavior somewhat different from those generated by other methods.The possible contributory role of carbene intermediates derived from ?,R(3s) excited states in E <-> Z photoisomerization of acyclic alkenes is also discussed.