Cyclization aromatic

The present method is successful with a wide variety of ketones (see Table). Cyclic ketones (entries 1-4, 8) produce benzoannelated products in excellent overall yields. There is no need to purify the intermediate both the nucleophilic addition of methallylmagnesium chloride and the aromatic cyclization take place cleanly. Acyclic ketones (entries 5-7) also provide high yields of benzoannelated product. Aromatic ketones are particularly interesting substrates for this reaction since they provide substituted biphenyls, which are potentially useful materials for liquid crystal synthesis and whose preparation through classical methodology is often not straightforward. The conditions for the cationic cyclization step can be modified to accommodate acid-sensitive functionality. For example, cyclization of 3 to 4, the latter a precursor for 3-methyl-8,14-dehydromorphinan, was accomplished in 77% yield by treatment of 3 at... 

The refractory compounds in the HMW DOM pool seems to be generated through abiotic reactions that act to link degradation products into macromolecules. These new chemical bonds create molecular structures that enhance the overall refractory nature of the DOM. The chemical changes lead to increased crosslinking, aromaticity, cyclization, esterification, and nitrogen depletion. The general types of chemical reactions responsible are oxidations, polymerizations, and condensations. Considerable debate exists as to whether these reactions are wholly abiotic or whether they are, at least in part, microbially mediated. 

Exclusive attack on N-l of HPs seems to occur with aromatic cyclizing agents, e.g., orthobenzoic ester (60JOC361), and in reactions of N-alkylated HPs (60JOC361, 60YZ1550). 

In a series of papers, Jacquesy and Jouannetaud have demonstrated the efficacy of aromatic cyclization reactions in HF SbF5 medium.784 l,3-Bis(methoxyphenyl) propanes and other substituted phenylpropanes 233 give substituted indenes (234) and tricyclic spiro enones (235) in the superacid medium844 (Scheme 5.84). 

An addition-elimination sequence was proposed for the intramolecular aromatic cyclization of a series of 4-aryl-alkenyl iodonium salts which were converted into dihydronaphthalenes [44] ... 

On the other hand, there is the question of the close relationship between coke formation (catalyst stability) and aromatics cyclization (catalyst selectivity) over the acid sites present in the zeolites. On naphtha reforming, coke formation is a bifunctional reaction requiring the dehydrogenation capacity of the metallic function and the condensation capacity of the acidic function. Therefore, it is interesting to... 

Stabilization process which is carried out in air (oxidative stabilization) constitutes the first and very important operation of the conversion of the PAN fiber precursor to carbon as well as activated carbon fiber. During stabilization, the precursor fiber is heated to a temperature in the range of 180-300 °C for over an hour. Because of the chemical reactions involved, cyclization, dehydrogenation, aromatization, and oxidation and cross linking occur and as a result of the conversion of CH N bonds to C=N bonds fully aromatic cyclized ladder type structure forms [36, 49]. 

Polyimides n Thermoplastic aromatic cyclized polymers of trimellitic anhydride and aromatic diamine. Have good tensile strength, dimensional stability, dielectric and barrier properties, and creep, impact, heat, and... 

While boron trihalide-mediated ether cleavage has been successfully applied in a number of organic syntheses, it was discovered that the BBr3-mediated demethylation of 2-methoxybiaryl systans could be problematic due to an intramolecular electrophilic aromatic cyclization (Schone 23.7). In these cases, 10-hydroxy-10,9-boroxarophenanthrenes are obtained as major products. 

A cascade reaction for the construction of spirobenzo[/t]chromanone and spiropyranone derivatives was achieved by a platinum-catalysed tandem cyclization/[l,2]-alkyl migra-tion/allyl shift of epoxy alkynyl allyl ethers followed an aromatic cyclization reaction (Scheme 142). ... 

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