Broad Scope Extra-Annular [4 + 2] Cycloaddition of o-Carboryne with Styrenes: Efficient Route to Carborane-Fused Polycyclics

o-Carboryne (1,2-dehydro-o-carborane) generated in situ from the precursor 1-OTf-2-Li-o-1,2-C₂B₁₀H₁₀ undergoes an efficient extra-annular [4 + 2] cycloaddition with styrenes at room temperature to give a series of carborane-fused polycyclics in good to high isolated yields. This reaction is compatible with many functional groups and has a very broad substrate scope. Further transformations of the resultant products have been carried out, affording various multi-functionalized o-carboranes.