By STEVEN WOLFF* and WILLIAM C. AGOSTA* (Laboratories of The Rockefeller University, New York, New York 10021) ... Summary Photolysis of 3-( 3-methylbut-3-eny1)cyclo- pent-2-enone (4) leads to the tricyc10[5.2.0.0~~~]nonane ... THE unreported hydrocarbon tricyclo [4.2.0.01v4]octane (1) has been called1 [4.4.4]fenestrane and a broken window in recognition of a formal relationship with its tetracyclic homologue (2). This latter compound, known as [ ...