Alkyl trifluoromethyl sulfones

Alkyl substituents can be incorporated directly into nitroheteroaromatic rings via the VNS reactions with carbanions of alkyl trifluoromethyl sulfones (Scheme 21) [91]. 

The 2-alkyl-3,4,5-trichloroisothiazolium trifluoromethyl sulfonates 77a-c were also obtained by N-alkylation of the corresponding isothiazole 74 but only in poor yields (28-31%) (78USP4281136, Scheme 22). 

The cyclopropane cyclizations by elimination of triflinic acid (CF3S02H) are readily effected by basic treatment of triflones (trifluoromethyl alkyl sulfones) with activated /-protons (equations 46 and 47)39. The cyclopropane diesters 45 are formed on treatment of 44 with potassium hydride in DMSO or sodium methoxide in methanol (equation 48). In contrast, the monoester 46 failed to give the desired cyclopropane40. Addition of carbanions derived from /f, y-unsaturated phenyl sulfones to a, /i-unsaturated carboxylic esters and subsequent elimination of benzenesulfinate ion give cyclopropanes possessing the unsaturated side chain and the ester function in trans positions (equation 49)41. 

Chiral derivatives of hemiacetal from fluoral have been prepared by adding an alcohol to fluoral in the presence of (l )-BlNOL— Ti(0—iPr)2 or by HPLC resolution of the racemate. The displacement of the sulfonate moiety from the tosyl derivative, by an alkyl lithium aluminate, affords the trifluoromethyl ether with inversion of configuration and an excellent chirality transfer (Figure 2.49). ° ... 

Although an a-CF3 group is known to retard. S n2 reactions of carbon nucleophiles with alkyl sulfonates, it has now been found that y-trifluoromethylated allylic acetals undergo 5k2 -type reactions with Grignard reagents in presence of catalytic amounts of CuCN and TMS-C1 without formation of 5N2 products.110 This provides an alternative means of introducing a carbon nucleophile adjacent to a CF3 group. 

The main use of A -fluoropyridinium salts is as fluorinating agents. A recent study of A-fluoropyridinium-2-sulfonates substituted with alkyl or trifluoromethyl groups reveals them to be powerful and selective fluorinating... 

Simple sulfonyl carbanions which do not contain additional carbanion-stabilising groups, e.g. carbonyl groups or heteroatoms, can be readily alkylated in high yield by modern techniques with the use of alkyllithiums and lithium amide bases. A number of allylic halides have been successfully used. In allylic halides, the halogen directly attached to the double-bonded carbon is relatively inert towards nucleophilic attack (Scheme 41). In this way, sulfones (96) can be transformed via desulfonation into vinyl halides (97) or into ketones (98) by hydrolysis (Scheme 41). In contrast to ordinary alkyl sulfones, triflones (99) can be alkylated under mildly basic conditions (potassium carbonate in boiling acetonitrile) (Scheme 42). The ease of carbanion formation from triflones (99) arises from the additional electron-withdrawing (-1) effect of the trifluoromethyl moiety. 

The vast literature on applications of PTC in substitution reactions is mainly restricted to nucleophilic substitution reactions with an anionic reagent. However, recently the use of PTC in electrophilic reactions, like diazotization andazocou-pling C-and N-nitrosation, C-alkylation, acid hydrolysis of esters, chloromethylation, nitrite-initiated nitrations, and so on have been reported(Velichko et al., 1992 Kachurin et al., 1995). Alkylbenzene sulfonates and lipophilic sodium tetrakis[3,5-bis(trifluoromethyl)phenylboranate are typical electrophilic PT catalysts. Lipophilic dipolar molecules of the betaine type and zwitterionic compounds also function well as PT agents for both nucleophilic as well as electrophilic reactions. 

The reaction between a carbanion derived from alkyl 3,5-bis(trifluoromethyl)phenyl sulfones and aldehydes affords, with good yields and stereoselectivities, the corresponding 1,2-disubstituted alkene through the Julia-Kocienski olefination reaction. This one-pot protocol can be performed using the phosphazene base at —78 °C and has been successfully used in a high yielding and stereoselective synthesis of various stilbenes such as resveratrol [47] (Scheme 5.28). 

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