A CO2-mediated base catalysis approach for the hydration of triple bonds in ionic liquids

Abstract

Herein, we report a CO₂-mediated base catalysis approach for the activation of triple bonds in ionic liquids (ILs) with anions that can chemically capture CO₂ (e.g., azolate, phenolate, and acetate), which can achieve hydration of triple bonds to carbonyl chemicals. It is discovered that the anion-complexed CO₂ could abstract one proton from proton resources (e.g., IL cation) and transfer it to the CN or CC bonds via a six-membered ring transition state, thus realizing their hydration. In particular, tetrabutylphosphonium 2-hydroxypyridine shows high efficiency for hydration of nitriles and CC bond-containing compounds under a CO₂ atmosphere, affording a series of carbonyl compounds in excellent yields. This catalytic protocol is simple, green, and highly efficient and opens a new way to access carbonyl compounds via triple bond hydration under mild and metal-free conditions.