The selective assembly
of the 1,4-oxathiin nucleus has been treated
as a powerful strategy to access this scaffold present in molecules
with very interesting properties. In this study, the chameleon-like
reactivity of pyridinium 1,4-zwitterionic thiolates is exploited to
assemble the 1,4-oxathiin core through a [3 + 3] annulation. The optimal
annulation partner has been found to be the iodonium ylide of the
cyclic 1,3-diketones. The developed protocol allows the synthesis
of a variety of bicyclic 1,4-oxathiin derivatives under very mild
conditions under copper(I) iodide catalysis. Access to benzoannulated
1,4-oxathiins has been achieved through iodine-mediated aromatization
of the initially obtained bicyclic compounds.