Metal catalysed hydroboration of vinyl sulfides, sulfoxides, sulfones, and sulfonates

The hydroboration of phenyl vinyl sulfide with catecholborane (HBcat) and pinacolborane (HBpin) has been examined with a number of rhodium complexes, all of which proceed with excellent regiocontrol in favour of the branched product PhSCH(B(OR)2)CH3. The corresponding linear product can be obtained exclusively in reactions employing [Cp*IrCl2]2 and HBcat. Catalysed hydroborations of (E)-2-(p-toluenethio)styrene with HBcat using Rh(acac)(dppp) gave predominant formation of one product while reactions using HBpin afforded several products arising from a competing C–S bond cleavage (acac = acetylacetonato, dppp = 1,3-bis(diphenylphosphino)propane). Although reactions of phenyl vinyl sulfoxide were complicated by a competing deoxygenation reaction, hydroborations of phenyl vinyl sulfone using HBcat once again gave regioselective formation of either the branched or linear products, depending on the choice of catalyst used to effect this transformation. Catalysed hydroborations of phenyl vinyl sulfonate were less chemo- and regioselective, yielding hydrogenation and diboration products in addition to the two hydroboration product isomers.

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