[2 + 2] Cycloaddition of o-Carboryne with Vinyl Ethers: Synthesis of Carborane-Fused Cyclobutanes

o-Carboryne (1,2-dehydro-o-carborane) is a very useful synthon for the synthesis of a variety of carborane-functionalized molecules. Using 1-Li-2-OTf-o-C₂B₁₀H₁₀ as a precursor, o-carboryne undergoes an efficient [2 + 2] cycloaddition with a large variety of vinyl ethers at room temperature to give a series of carborane-fused cyclobutanes in very good to high isolated yields. This reaction is compatible with many functional groups and has a very broad substrate scope ranging from alkyl- to aryl- and to silyl-substituted vinyl ethers. A stepwise reaction mechanism is proposed based on the control experiments, which is supported by DFT calculations. All new compounds have been fully characterized by ¹H, ¹³C, and ¹¹B NMR spectroscopy as well as HRMS spectrometry. Some are further confirmed by single-crystal X-ray analyses.