Herein, we report a novel strategy for the formation of copper carbene via the cycloisomerization of the π-alkyne–Cu­(I) complex from terminal alkynes and tropylium tetrafluoroborate. Mechanistic studies and DFT calculations indicate that the reaction undergoes the intramolecular cycloisomerization process from the π-alkyne–Cu­(I) complex to afford the copper carbene intermediate, followed by migratory insertion with the second terminal alkyne to afford the barbaralyl-substituted allenyl acid esters. In addition, we develop a mild and highly efficient Cu­(I)-catalyzed cross-coupling protocol to synthesize 7-alkynyl cycloheptatrienes that has a broad functional group tolerance and is applicable to the late-stage functionalization of natural products.

A direct and catalytic dehydrative esterification of carboxylic acids with alcohols is described. B(C 6 F 5 ) 3 is shown to be a highly effective catalyst for the Fischer esterification, providing esters in high to excellent yields. This esterification shows excellent chemo-and site-selective monoesterification of various polyols without any protection step, including bio-derived molecule glycerol.