Pd-catalyzed processes

The intramolecular version of this reaction is known [2]. It must be noted that in the initial reactions, P(o-To1)3 was used as part of the catalyst however, some diphosphane complexes such as 1,1 -bis(diphenylphosphino)ferreocene (dppf) and 2,2 -bis(diphenylphosphino)-l,l -binaphthyl (BINAP) showed improvements for the coupling of aryl bromides and iodides with primary alkyl amines [2]. These studies are comprehensively detailed in Ref. [2]. 

Aryl tosylates and mesylates can also be successfully used [14b]. 

Important structural features of diall lbiaryl phosphine ligands [12e] 

The cross-coupling reactions of hydrazines with aryl halides to give substituted hydrazines is very important from the point of view of nitrogen heterocyde synthesis (for example, indoles, indazoles, pyrazoles, and aryltriazoles, and before this report by Straddiotto s group [28a], there was no literature method for the Pd-catalyzed cross-coupling of hydrazine to aryl electrophiles. Hydrazines are difficult substrates because of their reducing power and the reactivity of the mono-arylated hydrazine product to further arylation. 

7-diaminophenothiazines display two reversible oxidations with remarkable semiquinone-formation constants. The potentials can be fine-tuned by the electronic nature of the remote substituents on the / -substituted aniline moieties. All these compounds qualify as weakly luminescent and highly suitable hole conduction molecules for moleculcu- electronics applications or charge transport layers in organic light-emitting diode (OLED) and organic fidd-effect transistor (OFET) devices. 

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Watanabe reports a new method for the direct conversion of o-choroacetaldehyde N,N-disubstituted hydrazones into 1-aminoindole derivatives 93 by palladium-catalyzed intramolecular ring closure of 92 in the presence of P Bu3 or the bisferrocenyl ligand 94 <00AG(E)2501>. When X = Cl, this cyclizative process can be coupled with other Pd-catalyzed processes with nucleophilic reagents (e.g., amines, azoles, aryl boronic acids) so as to furnish indole derivatives with substituents on the carbocyclic ring. 

As Scheme 1 illustrates, the Pd-catalyzed process includes the formation of hemiamidal 1 in the same manner as that in the Co-catalyzed process. However, the unique feature in this process is that hemiamidal 1 is converted to a-bromoamide 2, which is the key intermediate in this process. Then, the oxidative addition of 2 to the Pd(0) species forms alkyl-Pd complex 3. Subsequent insertion of CO to the carbon-Pd bond of 3 gives the acyl-Pd complex 4, which leads to the formation of the A -acyl-a-amino acid 5 through reductive elimination and hydrolysis. 

The categories of sequentially Pd-catalyzed processes in this chapter are based upon the initial process. These are Heck reactions, allylic substitutions, aminations, Sonogashira couplings, metallations, CH activations, cycloisomer izations and miscellaneous processes. 

Sequentially Pd-catalyzed processes have been serendipitous as well as designed. All this indicates a plethora of opportunities for inventing and discovering new methodologies in the near future. 

As another show case of a sequentially Pd-catalyzed process [31] a one-pot four-component synthesis of pyrazole 31 encompasses a coupling-addition-cyclo-condensation-coupling sequence where, without further catalyst addition, the Pd catalyst of the Sonogashira coupling is exploited in the terminal Suzuki coupling step (Scheme 22) [113]. 

As a consequence of the mild reaction conditions in the sequence to 3-halo furans 55 the palladium catalyst should be still intact to trigger another Pd-catalyzed coupling in the sense of a sequentially Pd-catalyzed process [31]. As a consequence, a sequential Sonogashira-deprotection-addition-cyclocondensation-Suzuki reaction, where the same catalyst system is applied in two consecutive significantly different cross-coupling reactions in the same reaction vessel should be feasible. Therefore, upon consecutive reactions of (hetero)aroyl chlorides 7 and THP-protected propargyl alcohols 54, Nal and PTSA, and finally, addition of 1.05 equiv of boronic acids 60 and sodium carbonate, the substituted 3-aryl furans 61 can be obtained in decent yields (Scheme 35). 

Disappointingly, a Heck reaction on 5-bromo-2-methoxymethyl-6-phenylpyridazin-3(2//)-one (172) afforded only a low yield of 5-alkenyl-2-methoxymethyl-6-phenylpyridazin-3(2//)-ones (232). The major compounds were dehalogenated substrate (230) and 6-substituted 2-methoxymethyl-4-phenylphthalazin-1 (2/7)-oncs (231). The formation of the latter compound depends on the alkene since when styrene was used no phthalazin-l(2//)-one formation occurred. In this case, 65% of 2-methoxymethyl-6-phenylpyridazin-3(2//)-one and 5% 2-methoxymethyl-6-phenyl-5-(2-phenylvinyl)pyridazin-3(2//)-onc could be isolated. The formation of alkyl (2-methoxymethyl)-1 -oxo-4-phenyl-1,2-dihydrophthalazine-6-carboxylates and (2-methoxymethyl)-1 -oxo-4-phenyl-1,2-dihydrophthalazine-6-carbonitrile, using alkyl acrylates and acrylonitrile as alkenes, respectively, can be rationalized by a tandem Pd-catalyzed process. 

Typically, the most common method for allyl cleavage is through a Pd-catalyzed process, but in the case of allyl phosphates, nucleophilic reactions are effective and often better because phosphate is such a good leaving group. 

A chiral Ir(I) catalyst derived from the amino-(2,2 -biphenoxy)phosphine 37 promotes the synthesis of optically active 3-amino-l-alkenes from 2-alkenols, which are activated by (Eto)5Nb/ l-Vinyl-l,2,3,4-tetrahydroisoquinolines are obtained in good yields in the Pd-catalyzed process. Enantioselectivity is induced by the atropisomeric 38. ... 

Bis[dicarbonylchlororhodium(I)] and bis[(l,5-cyclooctadiene)chlororhodium(I)], Epoxide opening. The monoepoxide of a diene is regioselectively attacked by nucleophile (ArNHR, ROH) at the allylic position using [Rh(CO)2Cl]2 as catalyst, affording anil-1,2-amino alcohols and alkoxy alcohols. The results are apparently complementary to those obtained from the Pd-catalyzed process. 

Coupling between an imino chloride aiv by cyclization." This Pd-catalyzed process 1 able decomposition occurs and the reaction ... 

Protection of alcohols. Ether formation from ROH and 4-XCf,H4CH2Br mediated by NaH in DMF is easily achieved. Such ethers are cleaved by Pd-catalyzed processes. 

Multicomponent Coupling Reactions. Tandem one-pot Pd-catalyzed processes have been developed that permit the coupling of three (or more) reactants in a single step. For example, allenes, aryl halides, and aryl boronic acids react in the presence of Pd(dba)2 and CsF to afford functionalized olefins (eq 25). In related transformations, in situ-generated benzynes have been... 

Regardless of the mechanistic interpretation, the Pd/AsPhj system has recently been extensively used. This has had a great impact on the development of the Stille reaction and other Pd-catalyzed processes. Indeed, this catalytic system has in many instances been found to give superior results to the corresponding phosphine analog. Moreover, it has made possible some reactions for which phosphine ligands have failed to work. ... 

Some of these allylpalladium complexes, Pd2(V-C3H5)2(/t-Cl)2 in particular, are important not only as precursors to a large variety of allylpalladium complexes, but also as Pd(0) sources in a variety of Pd-catalyzed processes. It is actually commercially available. 

Also interesting is the preparation of cationic palladium complexes, such as [MePd (PMe3)2]Xt i and [(C6F5)Pd(CO)(PPh3)]X,t considering the fact that cationic palladium complexes are believed to be the actual catalytic species in several Pd-catalyzed processes, an example of which being the copolymerization of alkenes and... 

Numerous examples of Heck-type reactions are known, where the common /3-H-elimination usually following the carbopalladation step is inhibited because of stractural or stereochemical reasons. Either the intermolecular reaction with an additional reagent or another cyclization reaction then terminates the Pd-catalyzed process. Such reactions are discussed below, again starting from substrates related to the substructure shown in Figure 1. 

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