Regiocontrolled Cleavage of Dialkyl Ethers Using Regenerative Borates as a Sustainable Alternative to Boron Trichloride

Ethers are ubiquitous functional groups in natural products, surfactants, and materials, making them valuable targets for chemical diversification. This report advances a previously reported method utilizing a 1:1 mixture of BBr 3 and BCl 3 to cleave unsymmetric dialkyl ethers with high regio‐ and chemoselectivity. In this new protocol, regenerable triaryl borates are used in place of BCl 3 , offering a more sustainable approach. Importantly, all boron‐containing byproducts from the reaction can be converted back into the triaryl borate, enabling full reagent recovery. The speciation of borate/BBr 3 mixtures is monitored by 11 B‐NMR and compared to the previously studied BCl 3 /BBr 3 system. Additionally, Design of Experiments (DOE) statistical analysis reveals a correlation between borate Lewis acidity and cleavage selectivity. The triaryl borate regenerated in situ from aqueous waste performs comparably to freshly prepared material in subsequent reactions. Overall, this system matches or exceeds the performance of the original BBr 3 /BCl 3 method across a broad range of dialkyl ether substrates.