Tandem isobenzofuran formation-Diels alder reactions in the coupling of carbene complexes with 2-alkynylbenzaldehyde derivatives featuring an alkyne-dienophile tether

The coupling of carbene complexes and 2-alkynylbenzaldehyde derivatives has been examined for systems where the alkyne is further linked to an alkene. This reaction proceeds via generation of an isobenzofuran followed by a stereoselective intramolecular Diels-Alder reaction, followed by opening of the resulting oxanorbornene ring. A variety of hydrophenanthrene derivatives and heterocyclic analogues have been produced in this reaction. In one case the intramolecular Pauson-Khand reaction is a competing process.