Vladimir Ivanov

Direct Arylation of Heterocycles: The Performances of Ferrocene-Based Polyphosphane Ligands in Palladium-Catalyzed CH Bond Activation

The palladium‐catalyzed direct arylation of alkylated‐ furan, thiophene, and thiazole and benzoxazole heterocycles with electronically and sterically deactivated bromoarenes was selectively and efficiently promoted by ferrocenyl polyphosphanes. In this Cuf8ffH bond activation reaction of heteroaromatics, the performances of polydentate di‐, tri‐, and tetraphosphane ligands were compared, showing that the triphosphane 1,1′,2‐tris(diphenylphosphino)‐4‐tert‐butylferrocene 3 was the most effective for the coupling. The introduction of more electron‐donating (iPr) or electron‐withdrawing (furyl) groups on the phosphorus atoms did not improve the ligand performances. The coordination behavior of 3 towards palladium(II) and other groupu200510 metals, NiII and PtII, was studied and the corresponding 1,2‐P chelating phosphorus complexes were isolated in high yields and fully characterized by multinuclear 1H, 13C, 31Pu2005NMR (3⋅PdCl2, 3⋅PtCl2) and X‐ray structures (3⋅NiBr2). It was found that the triphosphane ligand 3 was able to accommodate bidentate chelating cis coordination to group 10 metals, and additionally a much rarely described bis monodentate trans configuration. The combination of these two modes of coordination in a multimetallic species was clearly evidenced for the first time for a ferrocenyl polyphosphane. This versatility in bonding is a clear difference of coordination potential of this catalytically more efficient triphosphane compared to analogous ferrocenyl di‐ or tetraphosphanes.

C-Phosphorylation of Azoles in Synthesis of Novel Fused Phosphorus-Containing Heterocycles

Direct C-phosphorylation with phosphorus(III) halides in basic medium has proved to be an efficient and convenient method for the introduction of a variety of phosphorus functions in the electron-rich heteroaromatic1 compounds. When applied to functionalized pyrroles,2 this reaction has afforded a number of novel phosphorus-containing fused heterocycles. Herein, we report on our recent findings concerning the construction of phosphorus-containing fused heterocycles having azole nuclei. Readily available derivatives of 5-amino-1-aryl-3-methylpyrazoles— amides, ureas, and azomethines3—have been subjected to the phosphorylation with P(III) halides in basic medium to produce biand even tricyclic (as in the last case) heterocyclic compounds having an endocyclic phosphorus atom (Figure 1). We explored the same approach concerning 1,3-azoles, known to be phosphorylated via a different mechanism.4 We have shown that the amide 5 (X = CH) reacts with phosphorus tribromide as well as with dibromophenylphosphine in basic medium to yield the 4,5-dihydrobenzo[e]imidazo[2,1-c][1,4,2]diazaphosphinine derivatives, which could be converted into P(V) derivatives 8 and 95 (Figure 2).