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2-Heteroaryl-benzoxazoles

Aryl- and 2-heteroaryl-benzoxazoles (112, 113) were prepared by Pd-catalyzed three-component condensation of aryl halides with o-aminophenols and carbon monoxide followed by dehydrative cyclization [63, 64]. A variant of such methodology using o-fluorophenylamines in place of o-am 1 nophenols was used to synthesize arylbenzoxazoles. [Pg.401]

The Kalkhambkar R G et al. approach (2012) The synthesis of 2-aiyl- and 2-heteroaryl-benzoxazoles and benzothiazoles fiom Schiff bases by using catalytic amounts of Pd(OAc)2 in imidazolium ILs (bmim)BF and (bmim)PFg without ligands and/or additives has been reported (Scheme 7.22) [126]. [Pg.220]

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],... [Pg.202]

Palladium chemistry involving heterocycles has its unique characteristics stemming from the heterocycles inherently different structural and electronic properties in comparison to the corresponding carbocyclic aryl compounds. One example illustrating the striking difference in reactivity between a heteroarene and a carbocyclic arene is the heteroaryl Heck reaction (vide infra, see Section 1.4). We define a heteroaryl Heck reaction as an intermolecular or an intramolecular Heck reaction occurring onto a heteroaryl recipient. Intermolecular Heck reactions of carbocyclic arenes as the recipients are rare [12a-d], whereas heterocycles including thiophenes, furans, thiazoles, oxazoles, imidazoles, pyrroles and indoles, etc. are excellent substrates. For instance, the heteroaryl Heck reaction of 2-chloro-3,6-diethylpyrazine (1) and benzoxazole occurred at the C(2) position of benzoxazole to elaborate pyrazinylbenzoxazole 2 [12e]. [Pg.1]

Oxazoles and benzoxazoles are viable participants in the heteroaryl Heck reactions. In their monumental work published in 1992, Ohta and colleagues demonstrated that oxazoles and benzoxazoles, along with other rc-sufficient aromatic heterocycles such as furans, benzofurans, thiophenes, benzothiophenes, pyrroles, thiazole and imidazoles, are acceptable recipient partners for the heteroaryl Heck reactions of chloropyrazines [22b]. Therefore, treatment of 2-chloro-3,6-diethylpyrazine (27) with oxazole led to regioselective addition at C(5), giving rise to adduct 28. By contrast, a similar reaction between 2-chloro-3,6-diisobutylpyrazine (29) and benz[fc]oxazole took place at C(2) exclusively to afford pyrazinylbezoxazole 30. [Pg.330]

Similar results were obtained for the heteroaryl Heck reaction of iodobenzene or bromobenzene with oxazole and benzoxazole [23]. [Pg.331]

A plausible mechanism for the above reaction involves oxidative addition of the heteroaryl chloride to Pd(0) to provide Pd(II) intermediate 75, which subsequently inserts into benzoxazole to form the arylpalladium(II) complex 76. P-Hydride elimination of 76 would afford 11 with concomitant regeneration of Pd(0) for the next catalytic cycle. [Pg.18]

Oxazoles and benzoxazoles are viable participants in the heteroaryl Heck reaction, whereby the alkyl halide or aryl halide is coupled to the unfunctionalized oxazole. First developed by Ohta and colleagues, it was demonstrated that a diverse array of aromatic heterocycles can be substrates in the reaction with chloropyrazines. While substitution was expected to occur at the 2-position, the reaction with chloropyrazine as the aryl halide resulted in substitution at the 5-position. When benzoxazole is used as the coupling partner, substitution is effected at the 2-position. More recently, a systematic study by Strotman and co-workers has demonstrated that slight modifications of the reaction conditions can allow completely regioselective coupling at either the 2- or 5-position. ... [Pg.268]

Shao and coworkers employed a [NHC-Pd(II)-Im] catalyst in the C-2 arylation of oxazoles and benzoxazoles with less-expensive and readily available aryl chlorides (2014OL1984). Consequently, 5-aryloxazoles (16 examples 77—97% yield) and 5-(un)substituted benzoxazoles (26 examples 53—96% yield) readily coupled to aryl chlorides bearing an assortment of different functional groups with no significant impact on the reaction. Examples of coupled products using the heteroaryl chlorides and 2-chloropyr-idine, 3-chloropyridine, or 2-chlorothiophene are illustrated below. [Pg.125]

At the same time, Itami and coworkers described a very similar series of couplings of azoles (benzthiazoles, benzoxazoles, benzimidazoles, thiazoles, and imidazoles) with aryl and heteroaryl halides and triflates using nickel(ll) acetate-bipyridyl and nickel(II) acetate-dppf catalysts, with lithium t-butoxide in dioxan. The Ni(OAc)2. bipy catalyst system was optimal for aryl/heteroaryl bromides and iodides (Scheme 5.4, Table 5.3), and the Ni(OAc)2.dppf system was effective for aryl/heteroaryl chlorides and triflates (Scheme 5.5, Table 5.4). Reaction temperatures were 85°C for the former and 140°C for the latter, and in both cases 1.5 equivalents of lithium /-butox-ide was required, a considerably lower loading than required under Miura s conditions. Fortuitously, there are a number of final products common to both authors,... [Pg.114]

Direct Arylation of Benzoxazoles and Related Heterocycles. Benzoxazole 3 was functionalized with a variety of arenes and heteroarenes in the presence of catal)4ic amounts of [Pd(phen)2](PFe)2 (eq 3). In particular, heteroaryl iodides provided excellent yields of the comesponding products. The reaction... [Pg.107]

Direct Carbonylative Coupling. Unsymmetrical diaryl ketones were synthesized via the direct carbonylative coupling of aryl iodides and heteroarenes in the presence of catalytic [PdCl(cinnamyl)]2, l,3-bis(diphenylphosphino)propane (dppp) as the ligand, and stoichiometric Cul. Thus, heterocycles such as oxazoles, benzoxazoles, thiazoles, benzothiazoles, and imidazoles reacted, with 4-iodoanisole in 56-75% yields (eq 1). Aryl iodides containing a variety of electron-donating or electron-withdrawing substitutents were tolerated in the reaction (eq 2) however, aryl bromides provided only traces of products. The role of the stoichiometric copper salt was to form a heteroaryl-Cu species, which could easily transmetallate to Pd. No reaction was observed in the absence of the Cul additive. [Pg.516]

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. [Pg.664]


See other pages where 2-Heteroaryl-benzoxazoles is mentioned: [Pg.332]    [Pg.399]    [Pg.18]    [Pg.404]    [Pg.260]    [Pg.168]    [Pg.87]    [Pg.119]   
See also in sourсe #XX -- [ Pg.401 ]




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Benzoxazole

Heteroaryl

Heteroarylation

Heteroarylations

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