Cathodic cleavages

TABLE 4. Cathodic cleavage of some /1-ketosulphones by fixed potential electrolysis in DMF (after Reference 48) ... 

Benzylic, allylic and propargylic positions enhance the cathodic cleavage rate of C— heteroatom bonds as, for example, in the reduction of benzylic and allylic halides or alcohols56. Similar activated sulphones, due to their acidity, are in a class apart. Figure 8 shows the similitude between the cathodic behaviour of an allylic sulphone and its isomer, i.e., the corresponding vinylic sulphone when the electrolyses are run in an aprotic solvent. However, in the presence of an excess of proton donor, discrepancies appear. 

Cathodic cleavage 2.2.2- trichloro-l-(4-hydroxyphenyl)ethanol - 2.2- dichloro-l-(4-hydroxyphenyl)ethylene Japan 120 Pb cathode... 

The cathodic cleavage of CX- to CH-bonds can be achieved with a variety of substituents X, such as Hal, NR3+, PR3+, OTos, or epoxides. Generally, good yields, a high potential selectivity, and often good stereoselectivities are encountered (see also Chapters) [117-123]. Chemical reactions for similar conversions, which are well worked out, especially with regard to yield and selectivity, are the reduction of tosylates with LiAlH4 and halides with... 

R = Ar, R3CH=CH Scheme 7 Cathodic cleavage of benzyl ethers. 

Scheme 8 Cathodic cleavage of benzyl- and allylesters e.g. benzyl carbamate, yields 90-99%.

Scheme 3 Mechanism of cathodic cleavage of halogenated alkanes.

Scheme 1 Anodic dimerization of thiourea and cathodic cleavage of the dimer.

Scheme 46 Cathodic cleavage of hexa(thio- butyl)benzene.

Scheme 51 Cathodic cleavage and coupling competing in reduction of a,j6-ethylenic sulfoxides.

In nonaqueous media, the cathodic cleavage of N—S bonds occurs according... 

Scheme 57 Cathodic cleavage of sulfonamide for deprotection of amines.

The cathodic cleavage of dihalides may be a powerful route to a variety of heterocycles (Schemes 63 and 64) [86-88]. 

In cathodic cleavage, a C—X bond is reductively converted to a C—H bond. 

In cathodic cleavage, a C—X bond is mostly reduced to a radical anion that dissociates into a radical and an anion X . The radical is further reduced to an anion and protonated in the final step. 

Many reducing agents are capable of severing a carbon-halogen bond. Cathodic cleavage provides perhaps the most versatile method, and has been put to excellent use. The electrochemical variation of the Wurtz reaction constitutes a powerful method for the construction of a variety of rings, particularly strained systems. Dramatic examples are provided by the assembly of bicyclobutane (308) [89], bicyclohexene (310) [90-92], [2.2.2]propellane (312) [93], spiropentane (316) [94], j -lactams 318 [95], and a variety of small-ring heterocycles (320) [96,97]. 

A benzoyl benzoate substituent in 6-position of p-cyclodcxtrine can act as redox catalyst for the cathodic cleavage of a benzylester-cyclodextrine inclusion compound. Thus, a simple redox enzyme model was formed... 

Electrogenerated Bases Formed by Cathodic Cleavage Reactions.136... 

TABLE 8. Cathodic cleavage of dimethyldiphenylphosphonium bromide (Hg cathode, 20 °C) selectivity versus potential177. 

A control experiment established that LiClOi, has no effect on the homogeneous photolysis of the lithium salt of 2. At conversions of anion greater that 20%, the efficiency of dimer formation decreases. Whether this can be attributed to further oxidation of the anion derived from dimer or to cathodic cleavage of dimer is under investigation. 

In the case of alkyl-substituted aromatics, the predominant reaction path very often is side-chain acyloxylation. By using Pd-coated cathodes in an undivided cell, it is possible to avoid the formation of the side chain-substituted products, because under these conditions the benzyl ester undergoes cathodic cleavage into the starting compounds 161) ... 

Table 9. Cathodic cleavage of benzyl ethers 71) 0.15 M (C4H9)4NBr or 0.1 M (C4H9)4NI in DMF, Q = 2-2.2 F mop1...

Cathodic cleavage of chlorides, bromides and iodides has been extensively studied 78>, but only few examples of C—F bond cleavage have been reported. Cyclic voltammetry at 0.4 V s" showed 79) that in DMF with 0.1 M (C4H9)4NI, benzotrifluoride exhibits a peak at —2.61 V(SCE) but a,a-difluorotoluene and a-fluorotoluene react... 

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