1,3-Dipolar Cycloaddition of Nitrones to a Nitrile Functionality in closo-Decaborate Clusters: A Novel Reactivity Mode for the Borylated CN Group

The Z-configured nitrones –O+N­(Me)C­(H)­C6H4R2-p (R2 = OMe (2a), Me (2b), NO2 (2c)) react with the nitrile functionality of the closo-decaborate clusters [Bun4N]­[B10H9(NCR1)] (R1 = Me (1a), Et (1b), But (1c), Ph (1d)) in CHCl3 solution under mild conditions (20–25 °C, 16–18 h) to afford the products of cycloaddition: viz., the borylated 2,3-dihydro-1,2,4-oxadiazoles [Bun4N]­[B10H9{NaCR1ON­(Me)­CbH­(C6H4R2-p)}](a–b) (3a–l). This reaction represents the first example of boron-mediated 1,3-dipolar cycloaddition of allyl anion type dipoles, i.e. nitrones, to the nitrile group. Alteration of the lipophilic [Bun4N]+ counterion with the hydrophilic Na+ via the metathetical reaction with NaBPh4 in 3a,b,e,f allows the modification of their hydrophilic–lipophilic properties and, consequently, solubility. Compounds 3a–j and 5a–d were characterized by high-resolution ESI-MS, IR, and 1H, 13C­{1H}, and 11B­{1H} NMR spectroscopy. The structures of 3a,e,f were determined by single-crystal X-ray diffraction.