Synthesis of thioesters by reactions of carboxylic acids with tris(ethylthio)borane

Thioesters are obtained in high yield by reactions of carboxylic acids with tris(ethylthio)borane in a refluxing solvent. The reaction pathway is complex, involving initial production of carboxylic anhydrides and oxybis(diacyloxy-boranes), which are separately attacked by liberated ethanethiol or the excess of tris(ethylthio)borane