Irradiation of various methylated 2-(4-pentenyl)tropones affords regioisomeric formal[6π+2πand[87π + 2π]cycloadducts. The cyclooctadiene-containing [6π + 2π]adductsare produced as mixtures of stereoisomers. A self-consistent mechanistic scheme based upon evidence accumulated through the study of regioselectivity and stereoselectivity as a function of reaction conditions has been proposed. This mechanism includes several discrete intermediates en route to the final cycloadducts. Attempts to functionalize [6π + 2π] cycloadducts through vinyllithium addition led to unconventional products through unanticipated reaction pathways.