Rearrangements rearrangement/nucleophilic

Anomalous Fischer cyclizations are observed with certain c-substituted aryl-hydrazones, especially 2-alkoxy derivatives[l]. The products which are formed can generally be accounted for by an intermediate which w ould be formed by (ip50-substitution during the sigmatropic rearrangement step. Nucleophiles from the reaction medium, e.g. Cl or the solvent, are introduced at the 5-and/or 6-position of the indole ring. Even carbon nucleophiles, e.g. ethyl acetoacelate, can be incorporated if added to the reaction solution[2]. The use of 2-tosyloxy or 2-trifluoromethanesulfonyloxy derivatives has been found to avoid this complication and has proved useful in the preparation of 7-oxygen-ated indoles[3]. 

Rearrangement by nucleophilic aromatic substitution and aromatic mgrallon trom one hetero atom to another (O lo N or S lo O)... 

I. Dostrovsky, E. D. Hughes, and C. K. Ingold, XXXII. The role of steric hindrance, magnitued of steric effect, range of occurrence of steric and polar effects, and place of the Wagner rearrangement in nucleophilic substitution and elimination, Chem. Soc. 173 (1946). 

The Role of Steric Hindrance (Section G) Magnitude of Steric Effects. Range of Occurrence of Steric and Polar Effects, and Place of the Wagner Rearrangement in Nucleophilic Substitution and Elimination," JCS 149 (1946) 173194. 

Figure 6.17 Examples of rearrangements during nucleophilic fluorination.

In this Chapter are described the possible mechanisms of electrophilic substitution at saturated carbon, as a preliminary to the discussion of the kinetics of substitution. Additionally, there is a description of the nomenclature that has been used to date. There has been no general agreement on the nomenclature of the mechanisms of electrophilic substitution at saturated carbon, and the notation used in subsequent chapters in the present work can thus usefully be enumerated here. We deal first of all with the fundamental mechanisms, that is with mechanisms that do not involve rearrangement or nucleophilic (anionic) catalysis. 

A short review of the first 100 years of ketene chemistry covers haloketenes, Wolff (g) rearrangements, stereoselective nucleophilic attack, dimerization, cycloadditions, ketene-Claisen and -Cope reactions, bisketenes, and free radical processes.12 ... 

The oxidation of the metal complexes of l,10-phenanthroline-5,6-quinone is thought to proceed in a similar manner, with the first step being a benzilic acid rearrangement. Rearrangements of this type may also be followed directly in nickel(u) and cobalt(m) complexes of 2,2 -pyridil. The first step of the reaction involves nucleophilic attack on an O-bonded carbonyl group to form a hydrate, followed by a benzilic acid rearrangement. In this case, the benzilic acid rearrangement products may be isolated as metal complexes (Fig. 8-43). 

Wheland (1960) made the point in several ways that these principles could lead to absurd errors. When ethyl chloride is treated with hydroxide ion, we obtain ethanol, not dimethyl ether but when iso-bornyl chloride is treated in the same way we obtain camphene after a deep-seated skeletal rearrangement. Although nucleophilic substitution at an ethylenic center goes with retention (Miller and Yonan, 1957), the Walden inversion undercuts any general principle of minimum configurational change. Likewise, an early PLM representation of the... 

Examples include the synthesis of 3-amino-l,2,4-oxadiazoles starting from 3-acylamino-5-methyl-l,2,4-oxadiazole <2002H811> and 2-aryl-l,2,3-triazoles from l,2,4-oxadiazole-3-ketone arylhydrazones <1999T12885, 2006JOC5616>. Oximes, hydrazones, formamidines, and thioureas of the furazan series also undergo base-catalyzed mononuclear rearrangements <2004RCB1121>. Nucleophilic attack at N(3) takes place in the benzofuroxan series. For example, reaction with secondary amines leads to o-nitroarylhydrazines (Scheme 55). 

The reversion reaction can be probed by isotope labelling experiments and kinetic studies, and rearrangement and nucleophilic attack by labelling studies or, for sufficiently dissymmetric cyclopropanes, by a study of product structure often combined with labelling studies. 

Smiles rearrangement Intramolecular nucleophilic aromatic rearrangement of activated aromatic substrates. 416... 

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