Decarboxylative Borylation of Aliphatic Esters via Visible-Light Photoredox Catalysis

Alkylboronates serve as pivotal intermediates in synthetic chemistry; however, their preparation through mainstream methods—such as transmetalation, hydroboration, or transition-metal-catalyzed borylation of (pseudo)halides—typically demands strictly anhydrous conditions and often exhibits limited compatibility with sensitive functional groups.

Herein, we report a mild, operationally straightforward, and versatile alternative: a decarboxylative borylation of readily available alkyl N-acyloxy-phthalimide esters under visible-light photoredox catalysis. This new protocol directly addresses the common synthetic challenges by proceeding efficiently under ambient conditions, utilizing non-anhydrous solvents, and critically, requiring no stoichiometric sacrificial additives. The reaction is catalyzed by an inexpensive iridium photosensitizer ([Ir(ppy)₂dtbpy]PF₆) upon irradiation with compact fluorescent light, employing tetrahy-droxydiboron as the boron source. A broad range of primary and secondary alkyl boronic acids are obtained in good-to-excellent yields. These products, which can be isolated as air-stable trifluoroborates after a simple KHF₂ workup, tolerate a diverse array of functional groups, including esters, ethers, halides, and heterocycles, highlighting the exceptional chemoselectivity of this radical-based pathway. Mechanistic investigations, including control experiments, support a catalytic cycle initiated by the single-electron reduction of the redox-active ester.

This generates an alkyl radical, which subsequently engages with an in situ formed, base-activated diboron species to forge the critical C–B bond. The method provides a general and practical strategy for converting abundant, stable aliphatic carboxylic acids—via their activated derivatives—into valuable alkylboron building blocks under remarkably mild conditions, offering a complementary and robust tool for complex molecule synthesis.