With Aryl Bismuth Reagents

In the Arylation of Inorganic and Organic Substrates with Aryl Bismuth(V) Reagents. 

Barton and coworkers have explored the arylation of various nucleophiles including nitroalkanes using bismuth reagents.105 Reaction of 2-nitropropane with triphenylbismuth carbonate gives 2-nitro-2-phenylpropane in 80% yield.106 Recently, this arylation has been used for the synthesis of unusual amino acids. Arylation of a-nitro esters with triphenylbismuth dichloride followed by reduction gives unique a-amino acids (Eq. 5.68).107... 

Aryl chlorides can also be used as coupling partners for azabismocine reagents 2. In the coupling reaction with aryl chlorides, Pd(PPh3)4 was not an efficient catalyst, and Pd(OAc)2/l,l,-bis(diphenylphosphino)ferrocene (dppf) combination was found to be effective [54]. Not only the arylation, but also methylation, alkenylation and alkynylation reactions can be accomplished by using the corresponding bismuth compounds (Scheme 35). The addition of CsF improved the product yields. However, electron-rich aryl chlorides were unable to be coupled efficiently under these reaction conditions. 

A recent report has shown that tricyclopropylbismuth can be utilized in the cross-coupling reaction with aryl halides and triflates [57]. Representative examples are shown in Scheme 38. Addition of a base activator and excess of the bismuth reagents are necessary to obtain the coupling products in good yields, although more than one cyclopropyl group was transferred when 0.5 equivalents of... 

In the phenylation reaction of substituted anilines, the electronic nature of the substituents plays a role only on the reaction rate, not on the overall yield (4-methoxyphenyl 91% after 15 minutes and 4-nitrophenyl 90% after 16 hours). The steric hindrance is also a factor which influences the reaction in slowing down the reaction rate. To obtain good to excellent yields, an excess of bismuth reagent is then required with hindered substrates. For example, mesitylamine required 2.2 equivalents of triphenylbismuth diacetate to afford the AT-phenyl derivative in 92% after 24 hours. Moreover, triphenylamine was obtained in 23% yield after 48 hours by arylation of, iV-diphenylamine. A variety of aliphatic, alicyclic, heterocyclic and aromatic amines as well as hydrazines were N-arylated by this system. No reaction took place with a-amino acids but their esters were mono-iV-phenylated under... 

A variety of methods have been developed for the preparation of substituted benzimidazoles. Of these, one of the most traditional methods involves the condensation of an o-phenylenediamine with carboxylic acid or its derivatives. Subsequently, several improved protocols have been developed for the synthesis of benzimidazoles via the condensation of o-phenylenediamines with aldehydes in the presence of acid catalysts under various reaction conditions. However, many of these methods suffer from certain drawbacks, including longer reaction times, unsatisfactory yields, harsh reaction conditions, expensive reagents, tedious work-up procedures, co-occurrence of several side reactions, and poor selectivity. Bismuth triflate provides a handy alternative to the conventional methods. It catalyzes the reaction of mono- and disubstituted aryl 1,2-diamines with aromatic aldehydes bearing either electron-rich or electron-deficient substituents on the aromatic ring in the presence of Bi(OTf)3 (10 mol%) in water, resulting in the formation of benzimidazole [119] (Fig. 29). Furthermore, the reaction also works well with heteroaromatic aldehydes. 

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