Reactivity, alkyl halides with dioxide

Other electrophiles that react with in situ-generated perfluorocarbanions in elude epoxides [226] equation 47), carbon dioxide [227] (equation 47) acyl halides [228, 229, 230, 20, 232, 233] (equation 48), fluoroformates [23d] car bonyl fluonde [23S, 236, 237] hexafluorothioacetone (generated from its dimei) [238] (equation 48), an a-fluoroalkylamine f2J9] (equation 48), cyanuric fluoride [240], and reactive alkyl halides [247, 242 243, 244, 245] (equation 49) Interestingly, an in situ-generated carbanion will also react with dibromodifluoromethane ia a mechanism involving difluorocarbene [246] (equation 50)... 

The electrophilic character of sulfur dioxide does not only enable addition to reactive nucleophiles, but also to electrons forming sulfur dioxide radical anions which possess the requirements of a captodative" stabilization (equation 83). This electron transfer occurs electrochemically or chemically under Leuckart-Wallach conditions (formic acid/tertiary amine - , by reduction of sulfur dioxide with l-benzyl-1,4-dihydronicotinamide or with Rongalite The radical anion behaves as an efficient nucleophile and affords the generation of sulfones with alkyl halides " and Michael-acceptor olefins (equations 84 and 85). 

Normally, the most practical vinyl substitutions are achieved by use of the oxidative additions of organic bromides, iodides, diazonium salts or triflates to palladium(0)-phosphine complexes in situ. The organic halide, diazonium salt or triflate, an alkene, a base to neutralize the acid formed and a catalytic amount of a palladium(II) salt, usually in conjunction with a triarylphosphine, are the usual reactants at about 25-100 C. This method is useful for reactions of aryl, heterocyclic and vinyl derviatives. Acid chlorides also react, usually yielding decarbonylated products, although there are a few exceptions. Likewise, arylsulfonyl chlorides lose sulfur dioxide and form arylated alkenes. Aryl chlorides have been reacted successfully in a few instances but only with the most reactive alkenes and usually under more vigorous conditions. Benzyl iodide, bromide and chloride will benzylate alkenes but other alkyl halides generally do not alkylate alkenes by this procedure. 

Carbon dioxide is not the only nonflammable, biocompatible, and widely available solvent. Let us not forget about water. In particular, supercritical water oxidation and related reactive processes have shown a tremendous capacity for reducing toxic chemicals to innocuous constituents. Akiya and Savage have authored a recent review. Of particular interest is the section on hydrolysis in SCF water. Numerous references are tabulated according to chemical family. With regard to the more toxic compounds, Klein et al. have been especially active for many years and Tester et al. have focused on alkyl halides. ... 

The difluorovinyllithium 566 was initially prepared by in situ dehydrofluorina-tion-deprotonation of the TV.TV-diethyl carbamate derivative 568 with two equiv of LiTMP845 or LDA844,845 (Scheme 154). This intermediate 566 showed lower reactivity than the corresponding defluorinated system 561. Moderate to good yields were obtained with silicon, selenium and tin halides (38-80%)844,845,847 and alkyl triflates (71-91%)845, moderate reactivity being showed toward carbon dioxide and carbonyl compounds844,845,847. The reaction of intermediate 566 with aldehydes gave compound... 

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