Silver Triflate/p-TSA Co-Catalysed Synthesis of 3-Substituted Isocoumarins from 2-Alkynylbenzoates

In this paper, we describe the silver triflate/p-toluensulfonic acid co-catalysed synthesis of seventeen isocoumarins and two thieno[2,3-c]pyran-7-ones starting from 2-alkynylbenzoates and 3-alkynylthiophene-2-carboxylates, respectively. The reactions proceed with absolute regioselectivity under mild reaction conditions and low catalyst loading, to give the desired products in good to excellent yields. A conceivable reaction mechanism is proposed and supported by isotope-exchange tests, and 1H NMR studies and ad-hoc experiments.