Regioselective Pummerer rearrangement in [2.2]paracyclophanes

We investigated and rationalized a synthetic pathway to [2.2]paracyclophanedienes, that exploits the combination of the Pummerer rearrangement on a dithiacyclophane with a photochemical sulfur extrusion step and a base-catalyzed elimination step. The synthetic pathway is very effective for the symmetric, prototypical [2.2]paracyclophanediene. In the case of an asymmetric precursor, bearing two aromatic units with differing electronic properties, mass spectrometry coupled with gas chromatography analysis suggests that the Pummerer rearrangement installs the acetate groups on the methylene carbon atoms neighboring the perfluoroaryl moiety. The rearrangement occurs with a high regioselectivity. Such an unexpected result may be useful in the design of sophisticated [2.2]paracyclophane architectures for applications in catalysis and electronics.