Lactonization of 2-Alkynylbenzoates for the Assembly of Isochromenones Mediated by BF 3 ·Et 2 O.

A general and efficient lactonization method of readily available 2-alkynylbenzoates affording biologically important isochromenones has been realized via a solely BF3 center dot Et2O-mediated 6-endo-dig cyclization process under mild conditions. An alternative mechanistic pathway in which BF3 center dot 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.