In the presence of novel iron(II) chloride-diphosphine complexes and magnesium bromide, lithium arylborates react with primary and secondary alkyl halides to give the corresponding coupling products in good to excellent yields. High functional group compatibility is also demonstrated in the reactions of substrates possessing reactive substituents, such as alkoxycarbonyl, cyano, and carbonyl groups.
A catalytic amount of 1,2-bis(diphenylphosphino)benzene (DPPBz) achieves selective cleavage of sp(3)-carbon-halogen bond in the iron-catalysed cross-coupling between polyfluorinated arylzinc reagents and alkyl halides, which was unachievable with a stoichiometric modifier such as TMEDA; the selective iron-catalysed fluoroaromatic coupling provides easy and practical access to polyfluorinated aromatic compounds.
An enantioselective silaborative C−C cleavage of meso-methylenecyclopropanes (meso-MCPs) was achieved by using a palladium catalyst bearing a chiral monodentate phosphine ligand. The (R)-2-bis(3,5-dimethylphenyl)phosphino-1,1‘-binaphthyl gave the highest enantioselectivity in the reactions with (methyldiphenylsilyl)pinacolborane at 50 °C, affording derivatives of 2-boryl-4-silyl-1-butene in high yields with high enantiomeric excesses. The reactions of bicyclic MCPs that have fused five- to eight-membered rings gave the corresponding products with 89−91% ee, whereas a little lower ee was observed in the reaction of a non-fused MCP (81% ee). Synthetic applications of the products were demonstrated through synthesis of β-silyl ketones by H2O2 oxidation and synthesis of stereodefined homoallylic alcohols via homologation−allylboration sequence, in which the chiral β-substituent of the allylborane has critical impact on the diastereochemical outcome.
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