A rhodium catalyst induced ring opening of benzocyclobutenols with selective cleavage of the C(sp(2))-C(sp(3)) bond adjacent to the hydroxyl group. The site-selectivity markedly contrasted with that of their thermal ring-opening reaction. The rhodium-catalyzed ring opening led to the development of a new alkyne insertion reaction constructing a dihydronaphthalene framework.

Carbon-carbon bonds constitute the major framework of organic molecules and carbonhydrogen bonds are abundant in their peripheries. Such nonpolar s-bonds are thermodynamically stable and kinetically inert in general. Nonetheless, selective activation of those ubiquitous bonds may offer a straightforward method to construct and/or functionalize organic skeletons. Herein we describe ring expansion from orthocyclophanes to metacyclophanes occurring upon sequential action of light and a metal catalyst. Formally, specific non-strained carbon-hydrogen and carbon-carbon bonds are cleaved and exchanged without elimination of any leaving groups. Notably, the product is energetically uphill from the starting material, but the endergonic photocyclization step makes it possible to drive the transformation forward. The ring expansion is extended to the stereospecific synthesis of metacyclophanes possessing planar chirality, during which central chirality on a tertiary carbon is transferred to planar chirality.

Tetralins (tetrahydronaphthalenes) are synthesised from benzocyclobutenols based on the rhodium-catalysed site-selective ring opening followed by intermolecular/intramolecular conjugate addition of the resulting arylrhodium species to electron-deficient alkenes. The produced structures make a remarkable contrast with those available from the same compounds under thermal reaction conditions.