Synthesis of cephalosporin compounds

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

wherein A Θ 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;

R 3 is tert-butyldimethylsilyl, tert-butyl, 4-methoxybenzyl, 2-methoxybenzyl, or triphenylmethyl;

R 5 is triphenylmethyl, tert-butyl, tert-butoxycarbonyl, 2-trimethylsilylethoxycarbonyl, or 4-methoxybenzyloxycarbonyl;

R 6 is triphenylmethyl, tert-butyl, tert-butoxycarbonyl, 2-trimethylsilylethoxycarbonyl, or 4-methoxybenzyloxycarbonyl; and

LG is halo or —OC(O)R 18 , wherein R 18 is selected from the group consisting of C 1-6 alkyl and C 1-6 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.

2. The process of claim 1 , wherein:

R′ is tert-butyl; and

R 3 is 4-methoxybenzyl.

3. The process of claim 1 , wherein:

R 5 is tert-butyloxycarbonyl; and

R 6 is triphenylmethyl.

4. The process of claim 1 , wherein LG is chloro or —OC(O)CF 3 .

5. The process of claim 1 , wherein A Θ is selected from chloride, acetate, trifluoroacetate and bisulfate.

6. The process of claim 1 , wherein A Θ is trifluoroacetate or bisulfate.

7. The process of claim 1 , wherein A Θ is trifluoroacetate.

8. The process of claim 1 , wherein the palladium source is selected from the group consisting of: tris(dibenzylideneacetone) dipalladium(0), tris(dibenzylideneacetone)dipalladium(0)-chloroform adduct, tetrakis(triphenylphosphine)palladium, palladium(II) acetate, palladium(II) trifluoroacetate, palladium(II) chloride, palladium(II) bromide, and bis(acetonitrile)dichloropalladium(II).

9. The process of claim 1 , wherein the palladium source is tris(dibenzylideneacetone)dipalladium(0).

10. The process of claim 1 , wherein the palladium-binding ligand is selected from the group consisting of:

11. The process of claim 1 , wherein the palladium-binding ligand is:

12. The process of claim 1 , wherein the step of admixing a compound of formula (IIa) in the presence of reagents comprising (a) a palladium source and (b) a palladium-binding ligand forms a pi-allyl intermediate.

13. The process of claim 1 , wherein the palladium-binding ligand is present in a molar ratio of between about 1:1 to about 10:1 with respect to the molar amount of palladium in the palladium source.

14. The process of claim 1 , wherein the palladium-binding ligand is present in a molar ratio of between about 3:1 and about 10:1 with respect to the molar amount of palladium in the palladium source.

15. The process of claim 1 , wherein the palladium-binding ligand is present in a molar ratio of between about 4:1 and about 10:1 with respect to the molar amount of palladium in the palladium source.

16. The process of claim 1 , wherein the palladium-binding ligand is present in a molar ratio of between about 5:1 and about 10:1 with respect to the molar amount of palladium in the palladium source.

17. The process of claim 1 , wherein the palladium-binding ligand is present in a molar ratio of between about 6:1 and about 10:1 with respect to the molar amount of palladium in the palladium source.

18. The process of claim 1 , wherein the palladium source is present in an amount of from about 0.2 mole % to about 5 mole % with respect to the compound of formula (IIIa).

19. The process of claim 1 , wherein the palladium source is present in an amount of from about 0.5 mole % to about 5 mole % with respect to the compound of formula (IIIa).

20. The process of claim 1 , further comprising the step of removing the palladium by washing with an aqueous acidic solution after forming the compound of formula (II).

21. The process of claim 20 , further comprising the step of recovering the palladium, after the step of removing the palladium, by increasing the pH of the aqueous acidic solution and adding an oxidant to the aqueous acidic solution, thereby recovering the palladium.

22. The process of claim 1 , wherein the reagents further comprise (c) a salt additive which is selected from the group consisting of potassium trifluoroacetate, sodium trifluoroacetate, lithium trifluoroacetate, potassium triflate, sodium triflate, lithium triflate, silver triflate and copper sulfate.

23. The process of claim 1 , wherein the reagents further comprise (c) a salt additive which is potassium trifluoroacetate.

24. The process of claim 1 , further comprising the step of admixing the compound of formula (IIa):

wherein A Θ 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;

with a strong acid selected from trifluoroacetic acid and hydrochloric acid,

to form an admixture comprising a compound of formula (Va):

wherein A Θ is trifluoroacetate or chloride.

25. The process of claim 24 , further comprising the step of isolating the compound of formula (Va) wherein A Θ is trifluoroacetate or chloride comprising the steps of:

(a) extracting the admixture with a non-polar solvent; and

(b) adding from about 2 to about 6 volumes of acetonitrile to isolate the compound of formula (Va).

26. The process of claim 24 , wherein the strong acid is trifluoroacetic acid, and wherein the compound of formula (Va):

A Θ is trifluoroacetate.

27. The process of claim 26 , further comprising the step of isolating the compound of formula (Va) wherein A Θ is trifluoroacetate comprising the steps of:

(a) extracting the admixture with a non-polar solvent; and

(b) adding from about 2 to about 6 volumes of acetonitrile to isolate the compound of formula (Va).

28. The process of claim 27 , further comprising the step of filtering the solids to isolate the compound of formula (Va) wherein A Θ is trifluoroacetate.