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 BF ·Et O-mediated 6-endo-dig cyclization process under mild conditions. An alternative mechanistic pathway in which BF ·Et O 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.