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

The use of triaryl borates for highly selective ether cleavage is described. The borate is regenerable from the aqueous extract of a previous ether cleavage reaction without repurification, making use of low toxicity boron and phenolic waste. Such strategies for CO cleavage are expected to be broadly applicable to synthetic manipulations where management of waste is critical.

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 BBr₃ and BCl₃ to cleave unsymmetric dialkyl ethers with high regio- and chemoselectivity. In this new protocol, regenerable triaryl borates are used in place of BCl₃, 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/BBr₃ mixtures is monitored by ¹¹B-NMR and compared to the previously studied BCl₃/BBr₃ 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 BBr₃/BCl₃ method across a broad range of dialkyl ether substrates.

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