Mechanism of the Rearrangement

The mechanism of the rearrangement catalyzed by Pd(fl), typically by PdCl2(RCN)2, is explained by the oxypalladation of an alkene to form 810 as an intermediate, or cyclization-induced rearrangement. As a limitation, no rearrangement takes place when the allylie ester 812 is substituted at the C-2 position of the allyl group, while a smooth rearrangement of 811 takes place[500]. 

The general mechanism of the rearrangement of aryl and diaryl-thiazoles seems to exclude the zwitterion route. Instead it takes place through bending of thiazoles bonds (98.213). Moreover, tricyclic sul-fonium cation intermediates, after irradiation of deuterated phenyl-thiazoles, have been suggested by several workers (98). 

JCS(P1)2673 89H1121]. As proven by crossover experiments, interconversion of the tautomers occurs intermolecularly, an ion pair 37c being the intermediate in the dissociation-recombination mechanism of the rearrangement. 

The mechanism of the rearrangement is explained as shown in Scheme 19. Protonation of the 9-hydroxy group followed by its elimination and subsequent chloride attack at the 4a-carbon generates a chloroindolenine 126. Addition of water to the 9a-imine carbon atom of 126 gives 127. Concerted elimination of the chloride with rearrangement of the alkyl side chain attached to the 9a carbon atom results in 3,3-disubstituted oxindole structure 120a. 

An intramolecular mechanism of the rearrangement has been shown in the special ESR study (refs. 21, 22), conducted on the model radicals, generated by abstraction of a bromine atom from T2 " the rate constant K2, equal to (5.0 + 0.3) X 104 sec- at 22°C, has been also determined. In addition, fragmentation of radical... 

Since the exact mechanism of the rearrangement of unsubstituted amidoxime DMAD adduct 51 was unclear, we decided to undertake our own studies. These... 

Concerning the mechanism of the rearrangement, it is proposed to involve the addition of the nucleophilic nitrogen of the 1,3-ambident nucleophiles to C-6 (see Section III,A,2,a). This covalent adduct is in equilibrium with the open-chain diamidino compound 83 (R = OCH3, SCH3). Cycliza-tion into 84, followed by a base-catalyzed fragmentation of the nitrogen-carbon bond at N-3 and expulsion of the thiomethyl or methoxy anion, yields the 2-amino-4(5)-phenylpyrimidines (Scheme III.47). 

The mechanism of the rearrangement is an excellent practical industrial example of a broad type of rearrangement, one occurring with an electron-deficient oxygen. The mechanism is given in Fig. 10.2. 

The mechanisms of the rearrangements of the aminochromes in the presence of alkali or zinc acetate differ mainly in the method by which the two catalysts bring about essentially the same electronic changes in the aminochrome molecule.106... 

The (/ -complexes all undergo thermal rearrangement to /2, /4-bicyclo[4.2.1]nona-2,4,7-triene tricarbonyl complexes. The possible mechanism of the rearrangement of the molybdenum complex has been thoroughly investigated by deuterium labeling and kinetic studies228. 

On A Oj and more typically on ZnO, the selectivity shifts towards formation of the aldehyde (increasing 4/3 ratios, Table 2). There are also large differences in selectivity between the isomers. These are indicative of a change in the mechanism of the rearrangement. With increasing basicity of the oxides, the relative importance of basic sites in the ring opening increases. This results in an increased probability of formation of the double-bonded surface intermediate (Fig. 3), which can be transformed to both isomeric carbonyl compounds. 

An important consequence of the mechanism of the rearrangement step is that if the migrating group R is attached to the amide carbonyl via a chiral carbon atom the configration is retained in the product, thus generating a fully optically active amine from optically active starting material (e.g. 2-phenylpropanamide). 

Bauer G (2000) Reactive oxygen and nitrogen species efficient, selective and interactive signals during intercellular induction of apoptosis. Anticancer Res 20 4115-4140 Beckwith AU, Davies AG, Davison IGE, Maccoll A, Mruzek MH (1989) The mechanisms of the rearrangements of allylic hydroperoxides 5a-hydroperoxy-3p-hydrocholest-6-ene and 7a-hydro-peroxy-3(1-hydroxycholest-5-ene. J Chem Soc Perkin Trans 2 815-824 Behar D, Czapski G, Rabani J, Dorfman LM, Schwarz HA (1970) The acid dissociation constant and decay kinetics of the perhydroxyl radical. J Phys Chem 74 3209-3213 Benjan EV, Font-Sanchis E, Scaiano JC (2001) Lactone-derived carbon-centered radicals formation and reactivity with oxygen. Org Lett 3 4059-4062 Bennett JE, Summers R (1974) Product studies of the mutual termination reactions of sec- alkylper-oxy radicals Evidence for non-cyclic termination. Can J Chem 52 1377-1379 Bennett JE, Brown DM, Mile B (1970) Studies by electron spin resonance of the reactions of alkyl-peroxy radicals, part 2. Equilibrium between alkylperoxy radicals and tetroxide molecules. Trans Faraday Soc 66 397-405... 

One interesting example derived from the Di-rc-Methane rearrangement14 16). The overall mechanism of the rearrangement is depicted in Scheme 1. 

The mechanisms of the rearrangements have not been established but they may well proceed via a betaine intermediate similar to those considered for similar transformations of mesoionic isomers (Section 4.01.1.2(h)) (79JCS(P1)732). Ollis and Ramsden have treated this type of rearrangement in more detail in their review (76AHC(19)l). 

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