Rhodium-catalysed tetradehydro-Diels-Alder reactions of enediynes a rhodium-stabilized cyclic allene.

Efficient methods for the synthesis of fused-aromatic rings is a critical endeavour in the creation of new pharmaceuticals and materials. A direct method for preparing these systems is the tetradehydro-Diels-Alder reaction, however this is limited by the need for harsh reaction conditions. A potential, but underdeveloped, route to these systems is transition metal-catalysed cycloaromatisation of ene-diynes. Herein, tethered unconjugated enediynes have been shown to undergo a facile room-temperature Rh-catalysed intramolecular tetradehydro-Diels-Alder reaction to produce highly substituted isobenzofurans, isoindolines and an indane. Furthermore, experimental and computational studies suggest a novel mechanism involving an unprecedented and complex Rh/Rh/Rh/Rh redox cycle involving the formation of an unusual strained 7-membered rhodacyclic allene intermediate and a Rh-stabilized 6-membered ring allene complex.