Phenols palladium catalyzed

Examples of palladium-catalyzed reduction are 4-chloro-2,6-di-r-butyl-phenol to 2,6-di-t-butylcyclohexanone (750 psig, 25 C) with loss of halogen 24), 1,8-dihydroxynaphthalene to 8-hydroxy-1-tetralone 30), and 2,4-dimethylphenol to 2,4-dimethylcyclohexanone (27). 

A series of benzo[fc]benzo[2,3-cfjthiophen-6,9-diones 12 has been prepared in modest yields by palladium mediated cyclization of the precursors 13. However, the necessity to use stoichiometric amounts of the palladium source precludes cost effective preparation of the targets. The required substrates 13 may be constructed by palladium catalyzed reactions between the appropriate phenols with 2,3-dimethylbenzoquinone <06SC3319>. 

Zhang and coworkers have reported on a palladium-catalyzed carbon-sulfur cross-coupling of aryl perfluoroalkoxysulfonates with thiols (Scheme 7.78) [91]. The fluorous substrates were obtained from commercially available phenols by treatment with perfluorooctanesulfonyl fluoride (C8F17S02F) under basic conditions. Various thiols were reacted with a slight excess of the perfluorinated sulfonates in a... 

At first Smutny carried out the palladium-catalyzed reaction of butadiene with phenol using PdCl2 as a catalyst (28, 29). Phenoxybutene and o- and p-butenylphenols were obtained in low conversion and yield. When pyridine was added, 8-phenoxy-l,6-octadiene was obtained in low yield. However, 8-phenoxy-l,6-octadiene and 3-phenoxy-l,7-octadiene... 

The palladium-catalyzed arylation of 2-phenylphenols and naphthols shows an interesting feature of arylation of C-H bonds, leading to the formation of an (aryl)(aryloxy)palladium(n) intermediate.65,65a,65b The phenolates are suitable as precoordinating groups. The reaction of 2-hydroxybiphenyl with an excess of iodobenzene occurs regioselectively at the two ortho-positions of phenyl group under palladium catalysis (Equation (57)). In the case of 1-naphthol, the peri-position is phenylated (Equation (58)). 

Hydroarylation of alkynoates with phenols is applied to the synthesis of calanolides A 17 and B 18, which are active against AZT-resistant strains of HIV-1.163 The key step is the palladium-catalyzed coumarin formation reaction, as shown in Scheme 18. 

In an alternative strategy functionalized phenols, such as iodophenol, were involved in palladium-catalyzed carbonylation of alkynes or allenes, producing coumarin or chromone derivatives (Scheme 23) [130-133]. After oxidative addition of the iodoarene to the Pd(0) catalyst the order of insertion of either CO or the unsaturated substrate mainly depends on the nature of the substrate. In fact, Alper et al. reported that CO insertion occurs prior to allene insertion leading to methylene- or vinyl-benzopyranone derivatives [130]. On the contrary, insertion of alkynes precedes insertion of CO, affording couma-rine derivatives, as reported by Larock et al. According to the authors, this unusual selectivity can be explained by the inability of the acyl palladium species to further react with the alkyne, hence the decarbonylation step occurs preferentially [131-133]. 

Disubstituted 4-chloro-2-cyclobutenones 75 undergo the palladium-catalyzed cross-coupling reaction with vinyl- and arylstannanes 76 or vinylzir-conium reagents to give the 4-R sa,-2-cyclobutenones 77. Without isolation, these cyclobutenones 77 are rearranged to the substituted phenols 78 on thermolysis [38], Application of this method to the stannylated heteroaromatics 79 provides a synthetic route to the aromatic benzoheterocycles 80 [39]. (Scheme 27 and 28)... 

The preparations of aryl sulfides typically employ aryl halides as starting materials. The procedure described here makes use of the ubiquitous class of commercially available phenolic compounds in the form of aryl triflates, which expands the range of readily accessible aryl sulfides. Prior to this disclosure, the use of aryl triflates in a palladium-catalyzed process for the formation of aryl alkyl sulfides was unprecedented. This procedure appears to be general with regard to electronically neutral or electron-deficient aryl triflates (Table 1). The yields in Table I correspond to the initially disclosed procedure employing sodium (ert-butoxide as the base. Lower yields were obtained with the 4-nitro-... 

The 4- and 6-positions of pyrrolo[2,3-3]pyridines can be substituted via palladium-catalyzed cross-coupling reactions with the 4- or 6-halo-substituted derivatives (Scheme 3) <2001SL609>. Nucleophilic displacement of the 4-substituent of 6-chloro-4-nitro- and 4,6-dichloro-pyrrolo[2,3-/ ]pyridines takes place with phenols. Protection of the pyrrole nitrogen with a /3-trimethylsilylethoxymethyl (SEM) group affords good yields of the aryl ethers (Equation 3) <2006TL2069>. 

The formation of chromane derivatives has also been realised in the palladium catalyzed intramolecular nucleophilic substitution of allyl carbonates (Tsuji-Trost reaction). In most cases the reaction is accompanied by the formation of a new centre of chirality. Using Trost s chiral ligand the ring closure was carried out in an enantioselective manner. The asymmetric allylation of the phenol derivative shown in 4.20. was achieved both in good yield and with excellent selectivity.23... 

In fact, the role of copper and oxygen in the Wacker Process is certainly more complicated than indicated in equations (151) and (152) and in Scheme 10, and could be similar to that previously discussed for the rhodium/copper-catalyzed ketonization of terminal alkenes. Hosokawa and coworkers have recently studied the Wacker-type asymmetric intramolecular oxidative cyclization of irons-2-(2-butenyl)phenol (132) by 02 in the presence of (+)-(3,2,10-i -pinene)palladium(II) acetate (133) and Cu(OAc)2 (equation 156).413 It has been shown that the chiral pinanyl ligand is retained by palladium throughout the reaction, and therefore it is suggested that the active catalyst consists of copper and palladium linked by an acetate bridge. The role of copper would be to act as an oxygen carrier capable of rapidly reoxidizing palladium hydride into a hydroperoxide species (equation 157).413 Such a process is also likely to occur in the palladium-catalyzed acetoxylation of alkenes (see Section 61.3.4.3). 

Palladium-catalyzed cyclization of o-allylphenols to benzofurans has been extensively studied.11 As is usual, early systems were catalytically inefficient but continued studies led to substantial improvement. A wide range of catalyst systems work for this process. One of the most efficient, from a standpoint of catalyst turnover and chemical yield, was based on chiral TT-allylpalladium catalysts (equation 6), although the optical yields were low. y-Pyrones can also be efficiently synthesized by palladium(II)-cata-lyzed addition of phenolic OH groups to conjugated enones (equation 7).12... 

We recently reported the synthesis of a perfluoroalkylsulfonyl linker attached to TentaGel resin 13 (Fig. 6), which proves to act in a fashion similar to triflates as we had hoped, and demonstrated its application for the traceless cleavage of phenols using palladium-catalyzed reduction and Suzuki cross-coupling reactions.3,4... 

Fig. 10. Multiple derivatization of purines including palladium-catalyzed reaction at the poorly reactive C2 position, (a) NaBH(OAc)3, 1% HOAc, THF (b) 59 (0.5 equiv.), 2,6-dichloropurine (1 equiv.), DIEA (1.5 equiv.), BuOH 80° (c) R2OH, PPh3, DiAD (1.5 2 1.3) in excess, THF, RT (d) boronic acids (5 equiv.), 7% Pd2(dba)3, 14% carbene ligand, Cs2C03 (6 equiv.), 1,4-dioxane, 90°, 12 h (e) anilines (5 equiv.), 7% Pd2(dba)3, 14% carbene ligand, KO Bu (6 equiv.), 1,4-dioxane, 90°, 12 h (f) phenols (5 equiv.), 7% Pd2(dba)3, 28% phosphine ligand, K3P04 (7 equiv.), toluene, 90°, 12 h (g) primary or secondary amines (5 equiv.), 90°, 12 h.

Quite recently, Grigg and co-workers have based several of their ingenious multicomponent reactions on the combination of the above-mentioned palladium-catalyzed coupling reactions of allenes with a subsequent reaction in a one-pot operation. For example, the catalytic re-allylpalladium species generated from the carbopalladation of the allene with iodobenzene was captured by a phenolic nucle-... 

The Tsuji-Trost Reaction (or Trost Allylation) is the palladium-catalyzed allylation of nucleophiles such as active methylenes, enolates, amines and phenols with allylic compounds such as allyl acetates and allyl bromides. 

Saa, J. M. Martorell, G. Garda-Raso, A. Palladium-catalyzed cross-coupling reactions of highly hindered, electron-rich phenol triflates and organostannanes./. Org. Chem. 1992, 57, 678-685. 

Krotz A, Vollmuller F, Stark G, Beller M (2001) Salt-free c-c coupling reactions of arenes palladium-catalyzed telomerization of phenols. Chem Commun 195-196... 

The preparation of different (NHC) - Pd°(dvds) complexes allowed the authors to make a systematic comparison of structure/activity for the telomerization reaction [228]. This study showed that electron-withdrawing substituents on the carbene backbone destabilizes the catalyst and therefore enhance its reactivity. These catalysts are applicable to primary and secondary alcohol as well as phenols and represent the first industrially viable catalyst system for palladium-catalyzed telomerization of butadiene with alcohol. 

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