Ready Access to Benzannulated [5,5]-Oxaspirolactones Using Au(III)-Catalyzed Cascade Cyclizations

This work showcases an unprecedented Au(III)-catalyzed cascade cyclization of 2-(4-hydroxyalkynyl)benzoates to access benzannulated [5,5]-oxaspirolactones related to biologically active natural products. This reaction proceeds through an initial 5-endo-dig mode of hydroalkoxylation of the alkynol segment to give the oxocarbenium species (via cyclic enol-ether) followed by the addition of carboxylate onto the oxocarbenium that delivers the oxaspirolactone scaffold. While testing this method's scope, we found that the steric and electronic environment of the hydroxyl group could alter the reaction pathway that delivers isochromenone through a competitive 6-endo-dig mode of attack of the carboxylate onto the tethered alkyne.

Rhenium-catalysed reactions in chemical synthesis: selected case studies

This Perspective presents and discusses a selection of examples that reinforce the enabling and distinctive reactivity provided by homogeneous rhenium catalysis in chemical synthesis. Specifically, the ability for lower oxidation...

Lactonization of 2-Alkynylbenzoates for the Assembly of Isochromenones Mediated by BF3·Et2O

A general and efficient lactonization method of readily available 2-alkynylbenzoates affording biologically important isochromenones has been realized via a solely BF₃·Et₂O-mediated 6-endo-dig cyclization process under mild conditions. An alternative mechanistic pathway in which BF₃·Et₂O activates the carbonyl of the ester moiety, rather than the alkyne triple bond, was postulated on the basis of control experiment results. Gram-scale reaction and further application for the assembly of more complex molecules demonstrated the practicability of the protocol.

Silver triflate/p-TSA co-catalysed synthesis of 3-substituted isocoumarins from 2-alkynylbenzoates

A well-balanced composition of catalytic system partners makes the approach cheap, quick, regioselective, mild, general, scalable and high-yielding.