Meerwein reaction, preparation

Meerwein reaction, preparation of p-acety1-a-bromohydro-cinnamic acid, 51, 1 Mercuric acetate, 54, 71 reaction with cyclooctatetra- / ene, 50, 24... 

Meerwein reaction, preparation of p-acetyl-a-bromohydrocinnamic acid, 51, /... 

Malononitrile, alkylation of, S3, 24 Malononitrile, ferr-butyl-, 53, 21 Meerwein reaction, preparation of p-acetyl-a-bromohydrodnnamic add, 51,1... 

Preparative aspects of the Meerwein reactions are treated in comprehensive reviews by Rondestvedt (1960, 1976) and by Engel (1990, Table 107). It is interesting to note in the 1976 review that about two-thirds of all papers published between 1955 and 1974 originated from the Soviet Union. Only two examples of Meerwein reactions were published in Organic Syntheses (Reynolds and VanAllen, 1963 a Ropp and Coyner, 1963). The Meerwein reaction was extensively reviewed by Dombrovskii (1984) and by Saunders and Allen (1985, p. 594). 

Ganushchak et al. (1972, 1984) proposed to perform the Meerwein chloroarylation of ethylenic compounds using the preliminarily prepared aryldiazonium tetrachlorocuprates. They found that methyl, ethyl, butyl acrylate, methyl methacrylate, and acrylonitrile in the polar solvent reacted with tetrachlorocuprate. Chloroarylation products were obtained with better yields than when using the traditional Meerwein reaction conditions. 

This procedure has been used to prepare a variety of substituted a-bromohydrocinnamic acids 2 p-acetyl-a-bromohydro-cinnamic acid was prepared for the first time by this method. The method illustrates a typical application of the Meerwein reaction for the arylation of unsaturated substrates.3 In this reaction a catalytic amount of a copper(I) salt is used to reduce an aryl diazonium salt forming an aryl radical and a copper(II) halide. Addition of the aryl radical to an unsaturated substrate forms an alkyl radical that is reoxidized by the copper(II) halide present forming an alkyl halide and regenerating the copper(I) salt catalyst. In this preparation, the product, an a-bromo acid, is formed in an acidic reaction mixture and dehydro-halogenation does not occur. However, dehydrohalogenation... 

Preparation. The precursor, l-chloro-4- o-nitrophenyl)-2-butene (3), is prepared by the Meerwein reaction of diazotized o-nitroaniline (2) with butadiene in acetone in the presence of cupric chloride and sodium acetate. - Dehydrohalogenation with methanolic potassium hydroxide then gives the diene (4). ... 

Thus adding acetone increases the preparative value of the Sandmeyer reaction. It is assumed240 that the Sandmeyer and the Meerwein reaction occur by way of aryl radicals. 

The sulfonyl part 4 of flucarbazone-sodium (1) can be prepared by a classical Meerwein reaction from the aniline (5) prepared according to Refs. [24, 25] (Scheme 2.6.6). 

Bridgcd Sulfonamides The methods available for the preparation of the sulfonamide bridge at the 3 and 4 position of the pyrazole are somewhat limited by the type of reactions that can be supported at these positions. In contrast to this, numerous methods are available for the introduction of the sulfonamide at the 5 position. They include (a) Meerwein Reaction/amination (b) oxidative chlorination/amination and (c) metalation followed by trapping of the resultant anion with sulfur dioxide or an equivalent. 

Fully substituted pyrazoles (e.g. 82), are readily prepared by the reaction of a substituted hydrazine with ethyl(ethoxyalkylidene)cyanoacetates. Meerwein Reaction then provides the sulfonamide 83. This sulfonamide can be further elaborated to a number of derivatives (e.g.84). 

To meet the needs of the advanced students, preparations have now been included to illustrate, for example, reduction by lithium aluminium hydride and by the Meerwein-Ponndorf-Verley method, oxidation by selenium dioxide and by periodate, the Michael, Hoesch, Leuckart and Doebner-Miller Reactions, the Knorr pyrrole and the Hantzsch collidine syntheses, various Free Radical reactions, the Pinacol-Pinacolone, Beckmann and Arbusov Rearrangements, and the Bart and the Meyer Reactions, together with many others. 

Catalytic amounts of mercuric chloride are usually employed in this preparation. Aluminum isopropoxide is a useful Meerwein-Potmdorf-Verley reducing agent in certain ester-exchange reactions and is a precursor for aluminum glycinate, a buffering agent (see Alkoxides, metal). 

The procedure given is applicable to many other aulfonyl chlorides as well (see Table I). Solid sulfonyl chlorides are added as such. When heavy frothing occurs in the reduction (e.g., with p-nitrobenzenesulfonyl chloride), addition of 50 ml. of chloroform to the reaction mixture will eliminate the foam without reducing the final yield. When the sulfonyl chlorides were prepared according to Meerwein and co-workers, it was found advantageous to use the crude, damp sulfonyl chlorides, since these are more easily reduced than the dried or recrystallized materials. 

In the fourth and final chapter, Howard Haubenstock discusses asymmetric reduction of organic molecules. Within this general topic of wide and continuing interest, Haubenstock s chapter deals with chiral derivatives of lithium aluminum hydride, their preparation from suitable amino or hydroxy compounds, and their use in reducing carbonyl groups. Related reactions of the Meerwein-Ponndorf-Verley type or involving tri-alkylaluminum reagents are also presented. 

Another method, in particular for the preparation of alcohols from ketones involves the transfer of hydrogen from a hydrogen donor. The classic example is the commercially applied Meerwein-Ponndorff-Verley reaction, which uses stoichiometric amounts of Al(O Pr)3 to produce acetone and the alkoxides of the alcohols desired [31], The catalytic version of this reaction, employing... 

Mannich reaction, 1, 10 7, 3 Meerwein arylation reaction, 11, 3 24, 3 Meerwein-Ponndorf-Verley reduction, 2, 5 Mercury hydride method to prepare radicals, 48, 2... 

The reaction gives better yields with dienes, styrenes, or alkenes substituted with electron-withdrawing groups than with simple alkenes. These groups increase the rate of capture of the aryl radical. The standard conditions for the Meerwein arylation employ aqueous solutions of diazonium ions prepared in the usual way. Conditions for in situ diazotization by /-butyl nitrite in the presence of CuCl2 and acrylonitrile or styrene are also effective.106 107 108... 

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