Phosphines palladium-catalyzed cross-coupling

Additional examples of palladium-catalyzed cross-couplings, in particular with allenylzinc compounds, can be found elsewhere [11, 15, 36]. A systematic study comparing several chiral palladium phosphine catalysts in the reaction of 4,4-di-methyl-1,2-pentadienylzinc chloride and iodobenzene revealed that an enantiomeric excess of only 25% was obtained from the best catalyst combination PdCl2 and (R,R)-DIOP [15]. The synthetic value of these transformations of donor-substituted allenes as precursors is documented by the preparation of a/l-unsaturatcd carbonyl... 

The synthesis of phosphino sulfoximine 97 relied significantly on the successful development of methods pursued in parallel in our group. Whereas palladium-catalyzed cross-couplings between 53 and 98 proceeded in low yield, the copper catalysis with a combination of copper(l) iodide and cesium acetate worked well, affording 99 in up to 83% yield [78]. The resulting phosphine oxides 99 were then reduced to the corresponding phosphines 97 using a mixture of trichlorosilane and triethylamine (Scheme 2.1.1.33). 

Pyridylmethylphosphinates can be accessed, albeit in low isolated yield, by palladium-catalyzed cross-coupling of 2- and 3-pyridylmethyl chlorides with anilinium hypophosphites <2005T6315>. For example, 3-chloromethylpyr-idine hydrochloride reacts with anilinium hypophosphite in the presence of Pd(OAc>2, dppf, 1,4-diazabicy-clo[2.2.2]octane (DABCO), and (BuOTSi as esterification agent to give butyl (pyridine-3-ylmethyl)phosphinate 53 in 46% yield (Equation 37). This transformation proceeds in 24% yield when performed on 2-chloromethylpyridine. 

Both amido and pinacol derivatives of B-Si compounds 125 and 126 added to terminal and internal alkynes in the presence of a palladium244-246 or platinum(O) catalyst247 by a mechanism involving an oxidative addition-insertion process (Equation (39)).248 On the other hand, phosphine-free nickel(O) catalyst resulted in the dimerization of alkynes giving a Z,Z-isomer of l-silyl-4-borylbutadiene derivatives.249 Since the palladium-catalyzed cross-coupling at the C-B bond is faster than the G-Si bond of 137, a silylboration-cross-coupling sequence provided a method for the synthesis of 1-alkenylsilanes.246... 

Tetraki s(tri phenyl phosphine) palladium was prepared by treating palladium chloride, available from Matthey Bishop, Inc., with hydrazine hydrate 1n the presence of triphenyl phosphine according to an Inorganic Syntheses procedure. The submitters used a freshly prepared, shiny yellow, crystalline sample of the palladium complex. On standing for an extended period of time (> a few weeks), its color gradually darkens. Even such samples are effective in many palladium-catalyzed cross-coupling reactions, but have not been tested in this reaction. Tetraki s( tri phenyl phosphine) palladium is also available from Aldrich Chemical Company. 

Palladium and platinum form numerous alkyl complexes of the types M(R)(X)L2 and MR2L2, usually stabilized by phosphine ligands. The palladium compounds are prone to reductive elimination this is important in palladium catalyzed cross-coupling reactions (Section 21-14) ... 

Application of Sterically Demanding Phosphine Ligands in Palladium-Catalyzed Cross-Coupling leading to C(sp )—E Bond Formation (E = NH, OH, and F)... 

Phosphine ligands derived from 2-phosphino-substituted heterocycles and their applications in palladium-catalyzed cross-coupling reactions ... 

Ishikawa S, Manabe K (2007) Oiigoarene strategy for catalyst development hydroxyiated oligoarene-type phosphines for palladium-catalyzed cross coupling. Chem Lett 36 1302-1303... 

In another notable application of the palladium-catalyzed cross-coupling of nitrogen-containing organozincs, reagents derived from amino acids react with aryl halides in DMF using P(o-Tol)3, tris(ortho-tolyl)phosphine as ligand (Scheme 4.81) [5]. The approach is equally weU suited for the preparation of arylated a-amino acids [255, 256] such as 358 or fS-amino acids [257]. The use of PtBUj affords better results for the synthesis of proHno-homotryptophane derivatives [258]. 

Limited studies are focused on the coupling of primary and secondary phosphines with aryl electrophiles due to palladium-catalyzed aerobic oxidation of R PH to R PCO) [225], Palladium-catalyzed cross-coupling of primary or secondary phosphines has been reported with aryl iodides (Scheme 20.67) [226,227], Buchwald and coworkers utilized Pd(OAc)j-DTPF for the coupling of secondary aryl phosphines with aryl halides [256]. This system is also effective for the reaction of phosphines with aryl chlorides. 

There were a couple of reports of cross-coupling reactions of pyrazoles published. Palladium-catalyzed cross-coupling between 3,4-, and 5-halopyr-azoles 32 and H-phosphonates, H-phosphinates, and secondary phosphine oxides to give pyrazoles 33 was accomplished in moderate-to-good yields (13OL5550). 1,3,5-Triarylaminopyrazoles 35 were prepared by Ullmann coupling firom l,3-diaryl-5-aminopyrazoles 34 and aryl halides in the presence ofcopper(I) iodide (13T570). 

---