UC Irvine

The syntheses of borylated S- and O- heterocycles are reported via mechanistically distinct borylative cyclizations. These methods can proceed with a Au(I) catalyst (direct borylation, formation of B–X bond) or without (formal borylation). Commercially-available B-chlorocatecholborane was the boron source used in these studies. The borylated products furnished from these methods provide complementary functional group tolerance to existing borylation methods, as well as complementary regioselectivity. Borylated benzofurans, dihydrofurans, isocoumarins, alpha-pyrones, benzothiophenes, and dihydrothiophenes were synthesized using this borylative cyclization methodology. In the direct borylative cyclization pathway (chapter 2), the mechanism is proposed to proceed via Au(I)-induced cyclization via a boric ester, follow by transmetalation of the organogold intermediate to furnish the desired borylated heterocycle. In the formal borylative cyclization pathway (chapters 3–5), mechanistic studies revealed that B chlorocatecholborane preferentially coordinated with the C–C pi system instead of the heteroatom to induce cyclization. These methods generate borylated building blocks that can be further functionalized through various C–B sigma-bond transformations.