Phenols palladium-catalyzed intramolecular

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 connection with a total synthesis of frondosin B, the key intermediate shown below was synthesized by a sequential reaction of the phenol, the enyne and the bromide in a one-pot operation as shown <04OL457>. The palladium-catalyzed intramolecular C-0 bond formation between aryl halides and enolates was employed to make 2,3-disubstituted benzo[i> furans <04OL4755>. 

More recently, a palladium-catalyzed intramolecular C-H arylation with mesylated compounds was reported by Kalyani and co-workers. A sequential mesylation-arylation protocol using phenols as substrates vras described as well. This method allows for the synthesis of diverse heterocyclic motifs, including dibenzofurans, carbazoles, and indoles, in good yields (Scheme 2.30). The intermolecular aiylations were efficient for the coupling of azoles with electronically diverse mesylates. 

Cataiytic transformation has also been accomplished. Kawaguchi et al. reported the palladium-catalyzed intramolecular 0-arylation of 2-[2-(pseudo)haloaryl]phenols [14]. 2-(2-Chlorophenyl)phenol (68) was converted to dibenzofuran (69) successfully in the presence of palladium(II) acetate/phosphine ligand, but the authors did not explore the scope of this reaction (Scheme 23.26). In addition, they accomplished the synthesis of fused polycyclic compounds such as dibenzo[(i,fi ]benzo[l,2-fe 4,5-fc jdifurans 70 [14] and oxa[7]helicene 71 [17] using this methodology (Scheme... 

With aromatic bromides as the substrates, in 2009, Gevorgyan reported a concise procedure for the synthesis of sihcon-containing oxacydes via the palladium-catalyzed intramolecular C-H arylation. And the resulted sUyl oxacydes could be subsequently desUylated into the corresponding orf/ o-arylated phenols easily (Scheme 3.2) [12]. 

Phenol and its derivatives are the most common substrates for the construction of oxacycles in this approach. In 2000, Fujiwara and coworkers reported a palladium-catalyzed intramolecular addition reaction of aryl alkynoates to construct coumarins in a mixture of trrfluoroacetic acid and CH2CI2 at room temperature (Scheme 3.6) [21]. This method is simple and efficient to give the desired oxygen-containing heterocycles in high yields. However, this palladium-catalyzed C-H olefination reaction is only constrained to the electron-rich aromatic compounds owing to the inherent limitation of electrophilic metalation process. 

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). 

A palladium(ll)-catalyzed intramolecular hydroarylation of a,(3-unstaurated carboxylic acids with electron rich phenols provides straightforward entry to 4-aryldihydrocoumarins 1069 (Equation 419) <2000JOC7516>. 

Biaryl structures are found in a wide range of important compounds, including natural products and organic functional materials [8,80,81]. One of the most common and useful methods for preparing biaryls is the palladium-catalyzed coupling of aryl halides with arylmetals (Scheme 1, mechanism A). On the other hand, aryl halides have been known to couple directly with aromatic compounds as formal nucleophiles under palladium catalysis. While the intramolecular cases are particularly effective, certain functionalized aromatic compounds such as phenols and aromatic carbonyl compounds, as well as... 

Chemo- and regioselective synthesis of naphtho[2,3-c]chromenes result from the palladium-catalyzed reaction of 2-haloaryl aUenes with 2-alkynyl-phenols in refluxing 1,4-dioxane (Scheme 18) (14CC5891). Another palladium catalyst was involved in the intramolecular oxidative cyclization of 3-allyl-2 -hydroxyflavones to afford chromone[2,3-c]-2f/-chromenes in good... 

A new total synthesis of morphine 409 employing a palladium-catalyzed cou-phng as a key step started from the hydroisoquinoline derivative 407 to give dihydrocodeinone 408 (Scheme 8.81). This transformation constitutes a cascade of an intramolecular Heck carbopalladation and subsequent heterocyclization. The initially formed arylpalladium iodide species attacks the bridgehead position of the diene functionality in 407 to form a r-allylpalladium complex that is trapped by the internal nucleophilic phenol moiety (cf. Scheme 8.30). 

Newman et al. reported an approach to 2-bromobenzofurans using an intramolecular copper catalyzed C—O coupling of gm-dibromovinyl phenols (Scheme 24.29, disconnection D-2 and Scheme 24.31) [115]. This process is directly analogous to their palladium-catalyzed route to indoles via gem-dihalovinylaniline precursors (Scheme 24.3). Like the indole synthesis, further development of this chemistry has focused on harnessing the synthetic potential of the second bromine atom. To this end, several research groups have reported routes incorporating a tandem direct arylation leading to 2-aryl [116] and heteroaryl [27,117] benzoxazoles. 

As a further modification of Fujiwara s work, Kitamura and coworkers realized the construction of coumarins by palladium-catalyzed C-H olefination of phenols with acrylates and subsequent intramolecular esterification (Scheme 3.7)... 

Besides six-membered heterocycles, the construction of five-membered analogs by C-H olefination of phenol derivatives has also been reported. In 2011, Wang and coworkers reported a palladium-catalyzed oxidative cyclization of 3-phenoxy acrylates to construct benzofurans via an intramolecular aromatic C-H olefination (Scheme 3.13) [31]. In the presence of 5 mol% Pd(OAc)2/PPh3 and 2.0 equiv. of CF3C02Ag, benzofurans were obtained in good yields in... 

The transition metal-catalyzed addition of alcohols to unsaturated systems has not been widely investigated. Reports on addition of alcohols to 1,3-diene [24] or allene [25] have appeared but have very limited scope. We recently reported the palladium/benzoic acid-catalyzed inter- and intramolecular addition of alcohols to alkynes in which various acyclic and cyclic allylic ethers are produced [26], The Pd-catalyzed addition of alcohols to alkylidenecyclopropanes proceeds smoothly providing a powerful tool for synthesis of allylic ethers [27a]. An intramolecular version of the hydroalkoxylation has been demonstrated in which the phenol-tethered alkylidenecyclopropanes undergo facile cyclization to give exomethylene products [27b],... 

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