[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.