Thiophene-Fused Bisdehydro[12]annulene That Undergoes Transannular Alkyne Cycloaddition by Either Light or Heat

A new bisdehydro[12]­annulene derivative having a thiophene-fused
structure has been synthesized. This highly twisted π-conjugated
macrocycle with two acetylene moieties in close proximity produces
a [2+2]-type alkyne cycloadduct by either photoirradiation or mild
heating without any transition metals. Theoretical calculations reveal
that the thermal reaction proceeds through successive 8π and
4π electrocyclic reactions, while the photochemical reaction
is an asynchronous concerted [2+2] cycloaddition. The fused structure
with the less-aromatic thiophene ring is crucial for achieving this
reaction. The cycloadduct, thiophene-fused biphenylene, has significant
potential as a new polycyclic π-scaffold for electronic applications.