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 important targets for chemical diversification strategies. This report improves upon a previous method utilizing a 1:1 mixture of BBr3 and BCl3 to cleave unsymmetric dialkyl ethers with high regioselectivity and chemoselectivity. The versatility of the mixed boron trihalide reaction was demonstrated in the complex setting of lignocellulose separation, where the method provided remarkably high-quality lignin. Motivated by the potential for large-scale application, our new protocol employs regeneratable triaryl borates in place of BCl3. All boron waste from the reaction can be converted back to triaryl borate for subsequent reactions. Triaryl borate regenerated from unpurified aqueous waste performed equally well to pure triaryl borate. Further, the reaction compares favorably to the original BBr3/BCl3 method across a wide variety of dialkyl ether substrates.