Regiochemistry of intramolecular [2+2] photocycloadditions of oxygenated 6-alkenyl-3-alkoxy-2-cyclohexenones is studied. Application of this methodology to construct a key intermediate [3.3.2] bicyclic skeleton of ryanodol is described as well. Irradiation of (3-butenyl)compounds 3, 11, 14 and of (4-pentenyl)compound 6 afforded exclusively the linear photoadducts 4, 12, 15 and 7 respectively. Irradiation of allyl compound 25 brought the desired crossed photoadduct 26. The structures of the photoadducts 4, 7 and 26 were assigned based on spectroscopic analysis and confirmed by subsequent retroaldol cleavage reactions of the corresponding photoproducts. The regiochemistry of linear adduct 15 was deduced by a sequence of transformations. Retroaldol cleavage of the photoadduct 15, followed by transannular reductive coupling with SmI���, and hydrolysis of the protecting group provided triol 18. PDC oxidation of 18 gave [4.2.2] bicyclic triketone 20 and a cyclic hemiketal 21. Finally, Swern oxidation of 18 confirmed both isomers of photoproduct 15 are linear adducts. Selective retroaldol ring opening of compound 26 resulted in the formation of the bicyclo[3.3.1]nonane skeleton, amenable through a one carbon ring expansion to establish the core bicyclo[3.3.2]decane system in ryanodol. / Graduation date: 1998