Carbanions formation, photochemical

PhSSPh with retention/ or photochemically/ Methyl phenyl N-methyl-sulphoximide gives adducts with ketones after conversion into its carban-ion, from which either tertiary alcohols are obtained by Al-Hg reduction under neutral conditions, or alkenes by reduction in aqueous acid, thus providing an alternative to the Wittig methylenation reaction/ Oxosul-phonium ylides formed by N-dimethylation followed by carbanion formation with NaH are useful as alkylidene-transfer reagents/ Uses of sulphoximides in heterocyclic synthesis have been reported methyl phenyl sulphoximide reacts through N with ethoxymethylene malonate esters. ... 

This review is concerned with the formation of cation radicals and anion radicals from sulfoxides and sulfones. First the clear-cut evidence for this formation is summarized (ESR spectroscopy, pulse radiolysis in particular) followed by a discussion of the mechanisms of reactions with chemical oxidants and reductants in which such intermediates are proposed. In this section, the reactions of a-sulfonyl and oc-sulfinyl carbanions in which the electron transfer process has been proposed are also dealt with. The last section describes photochemical reactions involving anion and cation radicals of sulfoxides and sulfones. The electrochemistry of this class of compounds is covered in the chapter written by Simonet1 and is not discussed here some electrochemical data will however be used during the discussion of mechanisms (some reduction potential values are given in Table 1). 

The above reactions proceed via free radical coupling. An alternative system for photochemically driven hydrocarbon functionalization evidently proceeds via the carbanion, which is obtained from reduction of the initially formed free radical3. The carbanion reacts with acetonitrile to give, after in situ hydrolysis, the methyl ketone, e.g., formation of (tricyclo[3.3.1.13-7]dec-1-yl)ethanone6. 

Evidence has been obtained that the photodecarboxylation of benzannelated acetic acids in aqueous solution proceeds via carbanion intermediates 5H-dibenzo[a,d]cyclohepten-5-carboxyl-ic acid, for example, undergoes photodecarboxylation with a quantum efficiency of close to unity. The reactions of the -nitrobenzyl anion, generated by photochemically induced loss of carbon dioxide from -nitrophenylacetate anion, have been examined and a mechanism proposed to account for the formation of the corresponding bibenzyl derivative. Reductive decarboxylation of carboxylic... 

Photochemical carbon acid dissociation has been studied in considerable detail by Wan and his coworkers. The current work has examined the photochemical behaviour of the dibenzocycloheptene derivatives (149). The influence of substituents on the process was studied. A review has highlighted the photochemical methods for the formation of carbanions. Within the general framework of photodeprotonation of benzylic systems Wan and his coworkers have also reported the results of a study into the photochemical deprotonation of the thioxanthenium salts (150)-(153). The reactions are carried out by irradiation at 254 nm in dry acetonitrile under an argon purge. Prolonged irradiation of compound (150), for example, results in the production of (154) in 60% yield. The authors reason that this product is formed via the intermediacy of the... 

Decarboxylation of (175) occurs on its irradiation in an argon matrix at 10 K using 254 nm light. Spectroscopic analysis of the resulting matrix indicates the presence of a complex between carbon dioxide and the carbene (176). Tiaprofenic acid (177) undergoes facile photochemical decarboxylation, and this is reported to take place from an upper triplet excited state." A study of the transient photochemistry of 5-(p-toluyl)-l-methyl-2-pyrrolylacetic acid has been reported. Decarboxylation results in the formation of a carbanion in its triplet state. A laser-flash study using irradiation at 266 nm of the xanthene-9-carboxylate (178) has shown that the radical (179) is formed. This study used NaY zeolites and studied the oxidation of the radical within the cage structure. Calculations have indicated that decarboxylation of (180) and (181) and deprotonation of cycloheptatriene and cyclopentadiene affords the same anions (182) and (183), respectively. ... 

Cleavage of a carbon-carbon bond having suitable acceptor and donor groups also takes place photochemically giving rise to simultaneous formation of a carbocation and a carbanion, as shown in Scheme 5.6. 

Studies of the photochemical formation of benzyl carbanions have been reported for two systems this year. Ultra-violet light irradiation of (420) in aqueous acetonitrile resulted in formation of (421) exchange of the benzylic hydrogens of (420) was also observed when heavy water was used in the solvent. Compound (421) was shown to arise by two pathways a di-7r-methane rearrangement, and a 1,7-hydrogen shift followed by electrocyclic closure. The deuterium exchange reaction is presumed to occur due to... 

Catalytic antibodies have been produced to catalyze an impressive variety of chemical reactions. For instance, stable phosphonic esters (or lactones, respectively) have been used as transition state mimics for the hydrolysis of esters and amides [555-557], acyl transfer [558] and lactonization [559] reactions, which all proceed via a tetrahedral carbanionic intermediate. In some instances, the reactions proved to be enantiospecific [560]. Elimination reactions [561, 562], reductions [563], formation and breakage of C-C bonds [564,565] and even photochemical reactions [566] can be catalyzed. The cleavage of an ether [567] and cis-trans isomerization of alkenes have been reported [568]. 

---