Alkyne synthesis through coupling of gem -diborylalkanes with carboxylic acid esters

Alkynes are fundamental molecular building blocks of great importance in synthetic chemistry and materials science. The efficient construction of alkynyl functionality from widely accessible functional groups is therefore highly valuable. Here we report the development of a modular synthesis of alkynes through reaction of carboxylic esters with lithiated gem -diborylalkanes and aryl triflimides. 1 H, 13 C and 11 B NMR spectroscopic and X-ray crystallographic analyses identify and characterize an intermediate α-boryl lithium enolate, which upon triflation with an aryl triflimide followed by water quenching generates the alkyne product. The developed strategy allows a range of carboxylic acid esters to be converted into both internal and terminal alkynes, within a short reaction time, including the transformation of chiral α-substituted esters into chiral propargyl compounds without racemization. The method has been applied to the synthesis of 13 C-labelled alkynes, using 13 C-labelled gem -diborylmethane and 13 C-labelled carboxylic esters, which enables access to 13 C-labelled terminal alkyne fragments in drugs and natural products.