Electrochemically induced rearrangement

Cleavage of a C—S bond in the initially formed anion radical has been shown to be the first chemical step in the electrochemically induced rearrangement of 5,5-diarylbenzene-1,2-dicarbothioates to 3,3-bis(arylthio)phthalides in dimethylformamide. The reaction can be effected with 0.1 F/mol and is considered a kind of internal SRN1 reaction (Praefke et al. 1980). 

Under similar reaction conditions, some ketones such as (53) gave products via an electrochemically induced Favorskii rearrangement (Eq. 10) [89, 90]. 

Electrolysis of amides in MeOH containing the bromide ion efficiently led to products of the Hofmann rearrangement (for example, 119 to 120 Scheme 43) [131]. This reaction, named the electrochemically induced (E-I) Hofmann rearrangement, is achieved without any bromine and base under mild and neutral reaction conditions. 

Scheme 44 Electrochemically induced Hofmann rearrangement with insertion of an epoxy alcohol.

Scheme 45 Electrochemically induced Hofmann rearrangement of N-Boc glutamine with retention of configuration.

Figure 14.2 Electrochemically induced molecular rearrangements undergone by the copper catenate 12+/ +. In the text, the subscript 4 or 5 indicates the number of nitrogen atoms coordinated to the metal. This number is explicitly shown on the figure.

Fig. 13 Principle of the electrochemically induced molecular motion in a rotaxane copper complex. The stable, four-coordinate monovalent complex is oxidized to an intermediate tetrahedral divalent species. This compound undergoes a rearrangement to afford the stable, five-coordinate copper(u) complex.

The addition of thiols to a non-activated double bond is catalysed by In(OTf)3 and when applied to 6-methylhept-5-en-2-thiol results in cyclisation to the tetrahydrothiopyran (Scheme 44) <06CC332>. Tetrahydrothiopyran-2-nitrile has been obtained by a base or electrochemically induced Stevens rearrangement of the S-ylide, 1-cyanomethyl-tetrahydrothiophenonium bromide <06CL98>. 

Figure 6.11 An electrochemically-induced molecular rearrangement of a copper(I)-con-taining unsymmetricaV l -catenane ...

Fig. 7. Principle of the electrochemically induced molecular motions in a copper(I) complex pseudorotaxane. The stable four-coordinate monovalent complex is oxidized to an intermediate tetrahedral divalent species. This compound undergoes a rearrangement to afford the stable five-coordinate copper(II) complex. Upon reduction, the five-coordinate monovalent state is formed as transient. Finally, the latter undergoes the reorganization process that regenerates the starting complex [the black circle represents Cu(I) and the white circle represents Cu(II)]...

Recently, the electrochemistry of fullerenes and their derivatives has gained much attention [33]. Cgo, C70 and higher fullerenes were reduced electrochemi-cally, and six reduction waves were observed for both Cgo and C70 [34], as well as for most of the higher fullerenes [35]. The energy levels that were obtained from these experiments were mostly in line with MO calculations. The electrochemistry of numerous fullerene derivatives was studied to compare their electron affinities and energy levels with their parent fullerenes. Electrochemically induced isomer-izations can be observed in CV, as is the case in the rearrangement of fulleroids to methanofullerenes [36]. 

ET-induced cycloadditions of polycyclic olefins and cycloreversions of cyclobutane species have been studied by ESR spectroscopy [266]. Upon chemical and electrochemical reduction, 2,2 -distyrylbiphenyl rearranges by intramolecular coupling into a bis-benzylic dihydrophenanthrene dianion (Scheme 1), which can be either protonated to a 9,10 -dibenzyl-9,10-dihydrophenanthrene or oxidatively coupled to a cyclobutane species. It is interesting to note that the intramolecular bond... 

Electroswitching of structure takes place when a redox change induces a reversible structural or conformational process in a molecule, such as an electrochemically activated intramolecular rearrangement [8.259]. On the supramolecular level it consists of the electroinduced interconversion between two states of different superstructure. A case in point is the reversible interconversion of a double-helical dinuclear Cu(l) complex M2L22+ [8.260] and of a mononuclear Cu(ll) complex ML2+ in a sequential electrochemical-chemical process [8.261] ... 

The structure of diphosphallenic radical cations, generated from the allene ArP=C=PAr by electrochemical oxidation, has been examined using EPR spectroscopy. Ab initio calculations including correlation effects at the MP2 and MCSCF levels have determined that two rotamers exist compatible with Jahn-Teller distortion of the allene.146 Anodically generated radical cations of alkyl phosphites [(RO P] and silylphosphites [(RO)2POSiMe3] reacted with alkenes by initial attack at the C=C bond followed by electron transfer, deprotonation, and elimination of an alkyl or trimethylsilyl cation to form identical alkyl phosphate adducts.147 The electron ionization-induced McLafferty rearrangement of n-hexylphosphine afford the a-distonic radical cation CTEPH, the distinct reactivity of which suggests there is no... 

Under basic conditions, mesoionic 1,2,3,4-oxatriazoles 5 and 6 rearrange in alcohol solutions to the respective anhydro-5-hydroxy-thiatriazolium hydroxides and anhydro-5-hydroxy-tetrazolium hydroxides (Equation 2) <1979J(P1)732, 1996CHEC-II(4)679>. That rearrangement of 1,2,3,4-oxatriazole 5 (Ar = Ph) to 3-phenyl-5-anhydro-l,2,3,4-thiazolium hydroxide can be induced electrochemically, has been reported for the first time (Section 6.08.5.5) <1997MRC124>. 

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