Oxygenation palladium-catalyzed

C. Palladium-catalyzed reactions with oxygen nucleophiles. 

Chapter 11 focuses on aromatic substitution, including electrophilic aromatic substitution, reactions of diazonium ions, and palladium-catalyzed nucleophilic aromatic substitution. Chapter 12 discusses oxidation reactions and is organized on the basis of functional group transformations. Oxidants are subdivided as transition metals, oxygen and peroxides, and other oxidants. 

Monoanions derived from nitroalkanes are more prone to alkylate on oxygen rather than on carbon in reactions with alkyl halides, as discussed in Section 5.1. Methods to circumvent O-alkylation of nitro compounds are presented in Sections 5.1 and 5.4, in which alkylation of the a.a-dianions of primary nitro compounds and radial reactions are described. Palladium-catalyzed alkylation of nitro compounds offers another useful method for C-alkylation of nitro compounds. Tsuj i and Trost have developed the carbon-carbon bond forming reactions using 7t-allyl Pd complexes. Various nucleophiles such as the anions derived from diethyl malonate or ethyl acetoacetate are employed for this transformation, as shown in Scheme 5.7. This process is now one of the most important tools for synthesis of complex compounds.6811-1 Nitro compounds can participate in palladium-catalyzed alkylation, both as alkylating agents (see Section 7.1.2) and nucleophiles. This section summarizes the C-alkylation of nitro compounds using transition metals. 

A mild aerobic palladium-catalyzed 1,4-diacetoxylation of conjugated dienes has been developed and is based on a multistep electron transfer46. The hydroquinone produced in each cycle of the palladium-catalyzed oxidation is reoxidized by air or molecular oxygen. The latter reoxidation requires a metal macrocycle as catalyst. In the aerobic process there are no side products formed except water, and the stoichiometry of the reaction is given in equation 19. Thus 1,3-cyclohexadiene is oxidized by molecular oxygen to diacetate 39 with the aid of the triple catalytic system Pd(II)—BQ—MLm where MLm is a metal macrocyclic complex such as cobalt tetraphenylporphyrin (Co(TPP)), cobalt salophen (Co(Salophen) or iron phthalocyanine (Fe(Pc)). The principle of this biomimetic aerobic oxidation is outlined in Scheme 8. 

Although there are indeed only few reported methods of direct activation of molecular oxygen via transition metals, there are many reports of indirect oxidation. The majority of this research is based on palladium-based oxidation as summarized in equation 32. The palladium complex catalyzed oxidation reactions have been reviewed previously186 and also only very recently187 and in this book the palladium catalyzed oxidation of dienes and polyenes will be discussed separately and therefore will not be discussed... 

The Alder-ene cyclization of allylic silyl ethers represents a clever use of cycloisomerization chemistry, as the enol ether products can be easily unmasked to yield aldehydes. Palladium-catalyzed cycloisomerization of 1,6- and 1,7-enynes containing an allylic oxygen most often gives rise to 1,3-dienes (see Section 10.12.4.1). However, enynes of type 63 underwent facile Alder-ene cyclization to the corresponding five- or six-membered rings (Equation (40)) using both [CpRu(MeCN)3]PF6 41 and the Cp analog ([Cp Ru(MeCN)3]PF6, 64).53... 

Stille coupling (12, 56).1 The key step in a synthesis of (E)-neomanoalide (4) involves palladium-catalyzed coupling of an allyl halide with an a-stannylfuran. Thus 1 and 2 couple in the presence of Pd(dba)2 and P(C6H5), to form 3 as a 1 1 mixture of (E)- and (Z)-isomers in 66% yield. Conversion of 3 to 4 involves reduction (DIBAH) and selective singlet oxygen oxidation of a 2-silylfuran to a butenolide. 

Popp BV, Stahl SS (2007) Palladium-Catalyzed Oxidation Reactions Comparison of Benzo-quinone and Molecular Oxygen as Stoichiometric Oxidants. 22 149-189 Prashad M (2004) Palladium-Catalyzed Heck Arylations in the Synthesis of Active Pharmaceutical Ingredients. 6 181-204 Prestipino C, see Zecchina A (2005) 16 1-35 Pretraszuk C, see Marciniec B (2004) 11 197-248... 

The two oxygen-activating complexes [Co(L)j [L = salophen, tetra-tert-butylsalo-phen (55)] have been prepared and were also synthesized within dehydrated zeolite NaY using the intrazeolite ligand synthesis method [164]. These encapsulated metal complexes were shown to be capable of oxidizing hydroquinone and so were then used in a triple catalytic system to mediate the palladium-catalyzed aerobic 1,4-diacetoxylation of 1,3-dienes (Figure 5.28) [165]. The catalytic system involved [Pd(OAc)2], hydroquinone and the [Co(salophen)] complex in acetic acid (Co Pd diene hydroquinone LiOAc = 1 2.23 50 8.3 690, acetic acid, 25 °C,... 

The groups of Sigman and Stoltz have concurrently published the palladium-catalyzed oxidative kinetic resolution of secondary alcohols using molecular oxygen as the stoichiometric oxidant. Both communications also described a single example of a diol desymmetrization using a palladium catalyst in the presence of (—(-sparteine [Eqs. (10.42) ° and (10.43) ] ... 

Following our first report on the palladium-catalyzed reaction of vinyl triflates with olefins (Heck-type reaction), oxidative insertion of palladium(O) into the carbon-oxygen bond of easily available vinyl triflates ... 

Palladium-catalyzed approaches have been described and studied for the oxygenated series. Thus, treatment of 2,3-dibromo-l-propene 182 with the monoanion of catechol 181, generated with NaH, in the presence of Pd(PPh3)4 and anhydrous potassium carbonate, afforded 2,3-dihydro-2-methylene-l,4-benzodioxin 183 in 67% yield (Equation 31) <1998JA9283>. 

Abstract Palladium-catalyzed oxidation reactions are among the most diverse methods available for the selective oxidation of organic molecules, and benzoquinone is one of the most widely used terminal oxidants for these reactions. Over the past decade, however, numerous reactions have been reported that utilize molecular oxygen as the sole oxidant. This chapter outlines the fundamental reactivity of benzoquinone and molecular oxygen with palladium(O) and their catalyst reoxidation mechanisms. The chemical similarities... 

Palladium-catalyzed addition of oxygen nucleophiles to alkenes dates back to the Wacker process and acetoxylation of ethylene (Sects. 1 and 2). In contrast, catalytic methods for intermolecular oxidative amination of alkenes (i.e., aza-Wacker reactions) have been identified only recently. Both O2 and BQ have been used as oxidants in these reactions. 

Palladium-Catalyzed Allylic Alkylation of Sulfur and Oxygen Nucleophiles -Asymmetric Synthesis, Kinetic Resolution and Dynamic Kinetic Resolution... 

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