Palladium amine oxides

Both amine oxides related to pyridines and aliphatic amine oxides (/25) are easily reduced, the former the more so. Pyridine N-oxide has been reduced over palladium, platinum, rhodium, and ruthenium. The most active was rhodium, but it was nonselective, reducing the ring as well. Palladium is usually the preferred catalyst for this type of reduction and is used by most workers 16,23,84 158) platinum is also effective 100,166,169). Katritzky and Monrol - ) examined carefully the selectivity of reduction over palladium of a... 

A-Amine oxides can be reduced (deoxygenated) to tertiary amines. Such a reaction is very desirable, especially in aromatic nitrogen-containing heterocycles where conversion to amine oxides makes possible electrophilic substitution of the aromatic rings in different positions than it occurs in the parent heterocyclic compounds. The reduction is very easy and is accomplished by catalytic hydrogenation over palladium [736, 737], by borane [738], by iron in... 

Ranu and Banerjee developed a [bmim][OH] TSIL for oxidative homocoupling of terminal alkynes to 1,4-disubstituted 1,3-diynes in atmospheric conditions using Cu(ii) without using either palladium catalyst, amines, oxidants or organic solvents. Significant advantages stated by the authors include fast kinetics, high yields and mild reaction conditions. 

Gabriele B, Salerno G, Mancuso R et al (2004) Efficient synthesis of ureas by direct palladium-catalyzed oxidative carbonylation of amines. J Org Chem 69(14) 4741 1750... 

Aoyagi, Y., Mizusaki, T., Ohta, A. Facile and efficient synthesis of pyrroles and indoles via palladium-catalyzed oxidation of hydroxy-enamines and -amines. Tetrahedron Lett. 1996, 37, 9203-9206. 

Perhaps the best known alkyne semi-hydrogenation catalyst is that developed by Lindlar which comprises calcium carbonate-supported palladium, modified by addition of lead acetate and, often, quinoline to improve selectivity [51]. Selective hydrogenation of 1-bromo-ll-hexadecyne (Eq. 8) has been shown to occur in high yield and without hydrogenolysis of the carbon-bromine bond, over Lin-dlar s catalyst treated with aromatic amine oxides such as pyridine A-oxide... 

For synthesis of quinazoline derivatives, various coupling reactions have been utilized after synthesis of quinazoline-2,4(lH,3H)-diones via palladium-catalyzed oxidative coupling by Hirota et aL [187]. For example, synthesis of diarylquinazolines by iron-catalyzed cross-coupling reaction [188], and diamino quinazolinones by palladium-catalyzed amination [171] have been developed Synthetic applications to quinazoline alkaloids are given in Sect. 3. 

This chapter focuses on the subset of these reactions that have been studied most intensively and that draw from the stoichiometric reactions presented earlier in this text. Thus, the first sections of this chapter highlight certain aspects of hydrocyanation, hydrosilylation, disilylation, hydroboration, diboration, silylborations, and hydroami-nation. The last section presents aspects of palladium-catalyzed oxidation and metal-catalyzed oxidative amination of olefins. 

Copper compounds, besides being the most widely used co-catalysts for palladium re-oxidation, are themselves active in DMC formation. Amine-copper(II) complexes are very efficient in producing DMC from the methanol/CO system, even at room temperature. However, their exploitation on a technical scale failed, mainly due to water-sensitivity and ligand instability under oxidative reaction conditions. 

The palladium oxide catalysed reaction between [Re(CO)sX] (X = Cl, Br, I) and L, a group VB donor ligand, proceeds to give cis-[Re(CO)4XL] in high yields (>75%) when L has a cone-angle of less than 150 The amine-oxide assisted decarbonyation of [Re2(CO)10] in the presence of 1,1 -bis(diphenylphosphino)ferrocene (dppf) produces, under different conditions the following products ... 

Palladium-catalyzed oxidative amination reactions are proposed to occur by the same basic mechanism as Waeker eyclizations (Scheme 12.11, Nu = NR). Stahl and co-workers developed a catalytic system for oxidative amination using pyridine as a ligand," but found some key challenges in this system, similar to the alcohol oxidation developed by Sigman and co-workers (i) pyridine, a kinetically labile ligand, could dissociate under the reaction... 

Gabriele, B. Salerno, G. Mancuso, R. Costa, M. Efficient Synthesis of Ureas by Direct Palladium-Catalyzed Oxidative Carbonylation of Amines. J. Org.Chem. 2004, 69,4741 750. 

Abstract During the last decades a powerful set of protocols featuring C(sp )-N bond formation have emerged as convenient alternatives for the assembly of enamine and enamides. Those methods consist of mostly palladium-catalyzed oxidative amidations of alkenes and both palladium- and copper-catalyzed cross-couplings between generally vinyl halides or pseudohalides and amines or amides. In this review recent advances in both types of processes will be disclosed. Additionally, the synthetic value of the title processes will be illustrated by describing relevant total syntheses of natural products involving vinylation process as the key step. 

A recent example where amine ligands have made a significant impact is direct O2 palladium-catalyzed oxidations [2 c, 58, 59]. A key contribution which inspired much of the growth in the field was reported in 1998 by Uemura and coworkers where they discovered the combination of Pd(OAc)2 and pyridine as a system for aerobic alcohol oxidation (Scheme 5.18A) [60]. A greater than 2 1 ratio of pyridine to Pd(OAc)2 is required to avoid decomposition of the catalyst Mechanistic studies performed indicate pyridine not only acts to support Pd(0) during reoxidation with dioxygen, but also inhibits the rate of alcohol oxidation... 

Palladium-catalyzed oxidations are not the only systems to benefit from the use of amine hgands, as copper systems have also utilized diamine hgands for direct 02-coupled aerobic oxidations. As an example, (-)-Phbox, and (+)-PMP ligands have been successfully used in an asymmetric copper coupling of l,T-bi-2-naphthol units (Scheme 5.19) [67]. Very recently Porco and coworkers reported a Cu(I)/(-)-sparteine-mediated system for the enantioselective oxidative dearo-... 

Amine activatitMi pathway has been well studied in catalysis by lanthanides, early transition metals, and alkali metals. In metal amide chemistry of late transition metals, there are mainly two pathways to synthesize metal amide complexes applicable under hydroamination conditions [54], One is oxidative addition of amines to produce a metal amide species bearing hydride (Scheme 8a). The other gives a metal amide species by deprotonation of an amine metal intermediate derived from the coordination of amines to metal center, and it often occurs as ammonium salt elimination by the second amine molecule (Scheme 8b). Although the latter type of amido metal species is rather limited in hydroamination by late transition metals, it is often proposed in the mechanism of palladium-catalyzed oxidative amination reaction, which terminates the catalytic cycle by p-hydride elimination [26]. Hydroamination through aminometallation with metal amide species demands at least two coordination sites on metal, one for amine coordination and another for C-C multiple bond coordination. Accordingly, there is a marked difference between the hydroamination via C-C multiple bond activation, which demands one coordination site on metal, and via amine activation. 

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