A method giving simple access to various 1-(phenylthio)-4-substituted-1,3-dienes (5−10) is described. The influence of the different functionalizations introduced on the dienic systems has been tested in a set of classical [4 + 2] cycloaddition reactions. Both the endo/exo and regio selectivities have been investigated. While the endo compound is, as expected, the only or major isomer in all cases, the regio competition between sulfur and oxygen is in favor of the oxygen substituent in the case studied here, in contrast to related works. For one type of adduct, X-ray crystallographic analysis and NMR spectroscopy have been used in conjunction with ab initio and semiempirical AM1 calculations to determine the structure and conformations of products as well as the energetic pathway from the primary concave endo cycloadduct (28) to a rearranged bicyclic structure (39). The theoretical results fully support the occurrence of a photochemical [1,3] sigmatropic shift of the thiophenyl group.