Arylation, palladium-catalysed

Indoles with carbocyclic halogen or triflate substituents are potential starting materials for vinylation, arylation and acylation via palladium-catalysed pro-cesses[l]. Indolylstannanes. indolylzinc halides and indolylboronic acids are also potential reactants. The principal type of substitution which is excluded from such coupling reactions is alkylation, since saturated alkyl groups tend to give elimination products in Pd-catalysed processes. 

Carbon-carbon bond formation reactions and the CH activation of methane are another example where NHC complexes have been used successfully in catalytic applications. Palladium-catalysed reactions include Heck-type reactions, especially the Mizoroki-Heck reaction itself [171-175], and various cross-coupling reactions [176-182]. They have also been found useful for related reactions like the Sonogashira coupling [183-185] or the Buchwald-Hartwig amination [186-189]. The reactions are similar concerning the first step of the catalytic cycle, the oxidative addition of aryl halides to palladium(O) species. This is facilitated by electron-donating substituents and therefore the development of highly active catalysts has focussed on NHC complexes. 

The cycloaddition of alkynes and alkenes to nitrile oxides has been used in the synthesis of functionalised azepine systems <96JHC259>, <96T5739>. The concomitantly formed isoxazole (dihydroisoxazole) ring is cleaved by reduction in the usual way. Other routes to 1-benzazepines include intramolecular amidoalkylation <96SC2241> and intramolecular palladium-catalysed aryl amination and aryl amidation <96T7525>. Spiro-substituted 2-benzazepines have been prepared by phenolic oxidation (Scheme 5) <96JOC5857> and the same method has been applied to the synthesis of dibenzazepines <96CC1481>. 

By analogy with modern routes for the preparation of well-defined polyanilines (D ), palladium-catalysed cross coupling of 1,4-diiodobenzene and primary aryl- and alkyl-phosphines affords the comparatively short chain polymers (66a-c) (Mn= 1000-4000) (Scheme 20), that can be oxidised either by atmospheric... 

The direct arylation of heteroaryls is particularly attractive due to the fact that these moieties are present in many biologically active compounds [58], Recently, etinkaya and co-workers reported the direct arylation of benzoxazoles and ben-zothiazoles with aryl bromides catalysed by a bis-NHC-palladium complex [59], Also, Sames and co-workers have described the C-H arylation of different SEM-protected heteroarenes, catalysed by NHC-Pd complex 28 (Scheme 7.12, pathway a) [60],... 

Another methodology that is widely used for C-C bond formation is the Heck coupling (Heck, 1985 T.suji, 1995). The Heck reaction involves the palladium-catalysed arylation of olefinic double bonds (Eqn. (12)) and provides an alternative to Friedel-Crafts reactions for attaching carbon fragments to aromatic rings. 

A closely related reaction that is currently receiving much attention is the palladium-catalysed Suzuki coupling of arylboronic acids with aryl halides (Fu and Littke, 1998). For example, this technology has recently been applied by Clariant workers for the production of o-tolyl-benzonitrile (Eqn. (13)), an intermediate to a series of so-called angiotensin-II antagonists, a new class of antihypertensive drugs (Bernhagen, 1998). 

Quinazoline diones 54 were also available from 2-bromobenzoates via a palladium-catalysed jV-arylation of ureas<060L5089>. 

Vinyl ethers stannylated in the a-position undergo palladium-catalysed coupling with aryl hlides, as shown, for example, in reaction 64312 and 65313a. 

Herrmann WA, Brossmer C, Reisinger CP, Riermaier T, Ofele K, Beller M (1997) Coordination chemistry and mechanisms of metal-catalyzed C-C coupling reactions. Part 10. Palladacycles efficient new catalysts for the Heck vinylation of aryl halides. Chem Eur J 3 1357-1364 Iyer S, Jayanthi A (2001) Acetylferrocenyloxime palladacycle-catalyzed Heck reactions. Tetrahedron Lett 42 7877-7878 Iyer S, Ramesh C (2000) Aryl-Pd covalently bonded palladacycles, novel amino and oxime catalysts di- x-chlorobis(benzaldehydeoxime-6-C,AT)dipalla-dium(II), di- x-chlorobis(dimethylbenzylamine-6-C,A)dipalladium(II) for the Heck reaction. Tetrahedron Lett 41 8981-8984 Jeffery T (1984) Palladium-catalysed vinylation of organic halides under solid-liquid phase transfer conditions. J Chem Soc Chem Commun 1287-1289 (b) idem,... 

Y. Kayaki, Y. Noguchi, S. Iwasa, T. Ikariya, R. Noyori, An Effitient Carbonylation of Aryl Halides Catalysed by Palladium Complexes with Phosphite Ligands in Supercritical Carbon Dioxide , Chem Commun. 1999, 1235-1236. 

Djakovitch, L., Wagner, M., and Kohler, K, Animation of aryl bromides catalysed by supported palladium, / Organomet. Chem., 592, 225, 1999. 

Quaternary ammonium salts aid the transfer of the hypophosphite anion in the palladium-catalysed reduction of, for example, alkynes to alkenes, nitroarenes to aminoarenes, and in the hydrogenolysis of tetrazolyl aryl ethers to phenols [12-14], It has been demonstrated that the hydrogenolysis is ineffective when preformed tetra-n-butylammonium hypophosphite is employed in a dry homogenous organic solvent [13, 14], For optimum hydrogen transfer, the concentration of hypophosphite relative to the substrate must be controlled at a low level and this is most effectively accomplished with a two-phase system. 

Cluster or bimetallic reactions have also been proposed in addition to monometallic oxidative addition reactions. The reactions do not basically change. Reactions involving breaking of C-H bonds have been proposed. For palladium catalysed decomposition of triarylphosphines this is not the case [32], Likewise, Rh, Co, and Ru hydroformylation catalysts give aryl derivatives not involving C-H activation [33], Several rhodium complexes catalyse the exchange of aryl substituents at triarylphosphines [34] ... 

Special dibenzoxazepinones 86, obtained through the general method described in Fig. 16 and containing, as a third additional functionality, a triple bond, have been further cyclized via a palladium-catalysed hydroamination reaction (Fig. 17) [68]. In this way complex polycyclic systems 87 have been assembled in three steps, taking advantage of the three additional functions embedded in the starting component the aryl fluoride, the phenol and the triple bond. 

A palladium-catalysed carbonylative Sonogashira coupling was successfully carried out in the same setup [35]. Aryl iodides and phenylacetylene were submitted... 

Palladium catalysed copolymerization of aryl iodides with acetylene gas in an aqueous medium provides areneethynylene polymers and oligomers (Li et al., 1997)... 

The carbon skeleton of natural product galanthamine was prepared by the ring closure of an enantiopure aryl-cyclohexenyl ether. The transformation, run in the presence of a palladium-dppp catalyst and silver carbonate, led to the diastereoselective formation of the tricyclic product (3.25.). It is worth mentioning, that the chiral information in the ether intermediate was introduced in the palladium catalysed Tsuji-Trost reaction (N.B. the synthetic approach depicted in 3.13. and 3.25. are much alike).31... 

V-aryl-o-haloanilines can be converted into indole derivatives in a palladium catalysed oxidative addition, C-H activation sequence. The transformation has been utilized extensively in the preparation of polycyclic compounds. In a recent example, leading to the formation of the carbazole ring system, Larock and co-workers demonstrated that the formation of the... 

Heck-, Suzuki- and Stille-type Couplings - The Heck reaction, palladium-catalysed coupling of aryl or vinyl halides with alkenes or alkynes, is an extremely useful synthetic method. Only recently have Heck reactions been performed in aqueous media, probably due to the perception that water must be carefully... 

Arcadi, A. Cacchi, S. Marinelli, F. A Versatile Approach to 2,3-Disubsti-tuted Indoles through the Palladium-Catalysed Cyclisation of o-Alkynyltri-fluoroacetanilides with Vinyl Triflates and Aryl Halides, Tetrahedron Lett. 1992, 33, 3915-3918. 

A number of methods for the preparation of vinyl and allyl sulfones are available [1U9, 110], and the syntheses of vinyl sulfones from alkenes has been reviewed [116]. A simple one-step procedure of wide applicability makes use of a palladium-catalysed cross-coupling reaction between aryl and alkyl sulfonyl chlorides and substituted vinyl and allyl stannanes... 

Triarylphosphine ligands are of utmost importance in transition-metal catalysis. Thus, direct palladium-catalysed high-speed generation of these ligands from secondary phosphines and aryl halide building blocks would be a suitable and convergent synthetic route with high flexibility. Stadler and Kappe have shown that this method for the... 

Scheme 2.32 Palladium-catalysed synthesis of esters from aryl halides with Mo(CO)6 as the carbon monoxide source (DMAP = 4-dimethylaminopyridine).

Littke, A.F. and Fu, G.C., Palladium-catalysed coupling reactions of aryl chlorides, Angew. Chem., Int. Ed. Engl, 2002,41,4176-4211. 

Xu, L.J., Chen, W.P., Ross, J. and Xiao, J.L., Palladium-catalysed regioselective arylation of an electron-rich... 

Yang, B.H. and Buchwald, S.L., Palladium-catalysed amination of aryl halides and sulfonates, /. Organomet. Chem., 1999,576, 125-146. 

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