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.