Biaryl coupling Subject

Three methods for the construction of chiral polynaphthalenes have been described. In the first case, 2,2 -dihydroxy-6,6 -binaphthalenes were subjected to the optimized asymmetric oxidative coupling conditions, yielding the corresponding chiral polymers (a). It was found that each biaryl coupling step during the polymerization process is independent of existing axial chirality... 

Recently, chloro-, bromo-, and iodoben-zenes have been subjected to electroreduction using Ni(0) complex mediators to yield biphenyl. NiCl2L2 and NiBr2L2 [L= P(Ph)3, (Ph)2PCH2CH2P(Ph)2] have been used as catalysts [259-265]. Pro-tic media such as alcohols, that is, methanol, ethanol or alcohol-water mixtures are found to be suitable solvents for achieving the electrosynthesis of biaryls from aryl halides according to a procedure that involves a catalytic process by nickel-2,2 -bipyridine complexes [266]. Electrochemical cross-coupling between... 

Scheme 16 shows parallel syntheses of cyclic and acyclic amide compounds. Fluorous benzaldehydes were first subjected to reductive amination reactions. The resulting amines were then reacted with isocyanates to form substituted hydantoin rings 14 or with benzoyl chlorides to form amides 15. Purified F-sulfonates were used for palladium-catalyzed cross-coupling reactions to form corresponding biaryl 16 [31] and arylsulfide 17 [32] products, respectively. 

Biaryl synthesis constitutes one of the most important subjects in organic synthesis. The recently developed direct arylation reactions for the formation of aryl-aryl bonds have emerged as very attractive alternatives to traditional cross-coupling... 

Suzuki coupling of aryl halides with arylboronic acids is a powerful reaction for the construction of biaryl units in organic synthesis [34]. It is a versatile approach for cross coupling reactions, which have been the subject of intensive research. 

The Suzuki coupling was developed by Professor Akira Suzuki of Hokkaido University. The Suzuki coupling uses a boron compound (R-BYj) and an alkenyl, aryl, or alkynyl halide or triflate (RX) as the carbon sources, with a palladium salt as the catalyst. Bromides and iodides are the most commonly used halides chlorides are less reactive. Alkyl halides can sometimes be used but are subject to elimination. A base is also required. The boron compound can be a borane (R jB), a borate ester (R B(OR)2), or a boric acid (R B(OH)2), where R is alkyl, alkenyl, or aryl. The general reaction is shown in the following scheme, where X is halide or triflate and Y is alkyl, alkoxyl, or OH. A list of the types of components that can be used is given in Table 24.1. This reaction is one of the principal methods now used to prepare biaryls. 

When subjecting guaiacol (4) to this protocol, the anticipated 2,2 -biphenol was not found, but rather a 2,3 -coupling reaction occurred (Scheme 3). Biaryl 5 was the only product which was isolated. The unprecedented connectivity indicated a reaction pathway which involves the attack of a phenoxyl radical onto a closed shell species. The electrolysis of syringol (6) gave the biaryl 7 with exclusive selectivity. Since no leaving functionalities are involved, the selectivity and yield are remarkable [17]. 

The phenanthrene nucleus required for ( )-hasubanonine 79 (Scheme 17.16) was also assembled using RCM [35], in a similar way to that illustrated by luliano [26]. Initially, the biaryl compound 83 had to be assembled. This was done by synthesizing the aromatic iodide 84 and the aromatic pinacol ester 85. These compounds were then subjected to a palladium-mediated coupling, followed by conversion of the aldehydes to aUcenes, which proceeded smoothly to furnish 83. Compound 83 was then subjected to 2-Ru catalyst affording the required phenanthrene 86, which was then converted into ( )-hasubanonine 79 over a number of further steps. 

The atroposelective construction of the 6,6 -biaryl linkage was recognized as the key step in the synthesis of viriditoxin. Although many atroposelective couplings of complex molecules have been completed and have been the subject of many reviews,most of these approaches relied on either proximal stereogenic centers or covalently linked chiral auxiliaries. Our objective was to explore the influence of distal chiral centers on the catalytic oxidative dimerization of naphthopyran-2-ones using vanadium catalysis (Scheme 7). Assembly of naphthopyran-2-ones has been well studied and recently reviewed." The Staunton-Weinreb annulation or the Michael-Dieckmann condensation is ideally suited for the rapid... 

Chan et al. reported Suzuki coupling reaction between IL-supported iodobenzoates 91 and boronic acids (Scheme 11) [42]. The excess starting material and by-products of this process were removed by ether washing, and the ether-insoluble IL-bound biaryl products 92 were further subjected to cleave with ammonia/methanol to afford biaryl 93. 

The tetracyclic A/B/C/D ring core of (205)-camptothecin, one of the most potent antitumor natural products isolated from Camptotheca acuminate, was prepared by a combined directed ortho metallation/cross-coupling strategy. Snieckus showed that 2-bromo-6-methoxypyridine (152) could be sequentially treated with ter/-butyllithium (2 equiv) at -78 °C and anhydrous zinc bromide. The resulting organozinc species was then subjected to palladium-catalyzed cross-coupling reaction with triflate 153 to afford the biaryl 154, a precursor to the tetracyclic A/B/C/D ring core 155. 

Tandem cycloaddition of diiodotetrayne 162 with acetylene resulted in the efficient formation of 4,4 -diiodobiaryl 163 in 87% yield (Scheme 3.34) [49]. This novel biaryl building block was further subjected to cross coupling with p-biarylboronate... 

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