Synthesis of cephalosporin compounds

A process for preparing a compound of the formula (IIa):

• wherein AΘ is a pharmaceutically acceptable anion, selected from the group consisting of chloride, bromide, iodide, sulfate, bisulfate, toluenesulfonate, methanesulfonate, edisylate, maleate, monophosphate, biphosphate, ketoglutarate, trifluoroacetate, and trifluoromethanesulfonate;
• comprising the step of admixing a compound of the formula (IIIa), or a salt thereof,
• with a compound of the formula (X):
• wherein:
• R′ is tert-butyldimethylsilyl, tert-butyl, 4-methoxybenzyl, 2-methoxybenzyl, or triphenylmethyl;
• R3 is tert-butyldimethylsilyl, tert-butyl, 4-methoxybenzyl, 2-methoxybenzyl, or triphenylmethyl;
• R5 is triphenylmethyl, tert-butyl, tert-butoxycarbonyl, 2-trimethylsilylethoxycarbonyl, or 4-methoxybenzyloxycarbonyl;
• R6 is triphenylmethyl, tert-butyl, tert-butoxycarbonyl, 2-trimethylsilylethoxycarbonyl, or 4-methoxybenzyloxycarbonyl;
• and
• LG is halo or —OC(O)R18, wherein R18 is selected from the group consisting of C1-6 alkyl and C1-6 haloalkyl;
• in the presence of reagents comprising:
• (a) a palladium source, wherein the palladium source is selected from the group consisting of:
• bis(acetonitrile)dichloropalladium(II), bis(acetylacetonate)palladium(II), bis(benzonitrile)palladium(II) chloride, bis(dibenzylideneacetone)palladium, allylpalladium(II) chloride dimer, palladium(II) acetate, palladium(II) trifluoroacetate, palladium(II) chloride, palladium(II) bromide, tetrakis(acetonitrile)-palladium(II)tetrafluoroborate, tris(dibenzylideneacetone)dipalladium(0), tris(dibenzylideneacetone)dipalladium(0)-chloroform adduct, [1,2-bis(diphenylphosphinoethane] dichloropalladium(II), 1,1′-bis(diphenylphosphino)ferrocene-palladium(II)dichloride dichloromethane adduct, bis(tricyclohexylphosphine)palladium(0), bis(triethylphosphine)palladium(II) chloride, bis(triphenylphosphine)palladium(II) acetate, bis(triphenylphosphine)palladium(II) chloride, bis(tri-t-butylphosphine)palladium(0), bis[1,2-bis(diphenylphosphino)ethane]palladium(0), bis[tri(o-tolyl)phosphine]palladium(II) chloride, dichlorobis(tricyclohexylphosphine)palladium(II), tetrakis(triphenylphosphine)palladium(0), and trans-benzyl(chloro)bis(triphenylphosphine)palladium(II);
• and
• (b) a palladium-binding ligand selected from the group consisting of:
• to provide the compound of formula (IIa), or a salt thereof.