Oxidative cycloaddition of molecules with multiple thiophene cores

The oxidative cycloaddition of molecules with multiple thienyl-units to alkynes and alkenes is described. The reaction proceeds at room temperature. Yields can be increased upon the use of BF₃·Et₂O. Intermediates of the reaction are thiophene-S-oxides. An examplary isolation of a thiophene-S- oxide (16) in this series and its subsequent cycloaddition are shown. In the case of the oxidative cycloaddition of the thiophenes with alkenes 7- thiabicyclo[2.2.1]heptene-S-oxides (cf., 9) are formed. An X-Ray crystal structural analysis of 9a-H indicates the cycloaddition to be stereoselective (syn-endo). The SO-bridge in these bicyclic subunits could be extruded both thermally and oxidatively under PTC-conditions at room temperature. The products are novel orthocyclophanes.