Orthogonal Synthesis of Densely Functionalized Pyrroles and Thiophenes from the Reactions of Imidazo[1,5-<i>a</i>]pyridine Carbene-Derived Zwitterions with Electron-Deficient Alkynes

Abstract

1-Thiocarbamoyl imidazo[1,5-a]pyridinium inner salts, which were obtained readily from the addition of C,N-substituted heterocyclic carbenes imidazo[1,5-a]pyridine-1-ylidenes to isothiocyanates, are powerful ambident nucleophilic zwitterions. They acted as nitrogen nucleophiles toward ethyl propiolate to produce polyfunctionalized pyrrole derivatives in high yields. When treated with dimethyl acetylenedicarboxylate, they behaved exclusively as sulfur nucleophiles to afford fully substituted thiophenes in excellent yields. This work provides highly efficient orthogonal synthesis of polyfunctionalized pyrroles and thiophenes that were not easily obtained by other chemical means.