Friedel–Crafts Alkylation of Arenes with 2-Halogeno-2-CF₃-styrenes under Superacidic Conditions. Access to Trifluoromethylated Ethanes and Ethenes

Abstract

The formation of the corresponding benzyl cations [ArHC(+)-CH(X)CF3] takes place under protonation of E-/Z-2-halogeno-2-CF3 styrenes [ArCH═C(X)CF3, X = F, Cl, Br] in superacids. The structures of these new electrophiles were studied by means of NMR and theoretical DFT calculations. According to these data, in the case of bromo derivatives, the formed cations, most probably, exist as cyclic bromonium ions; however, in the cases of chloro and fluoro derivatives, open forms are more preferable. Subsequent reaction of these benzyl cations with arenes proceeds as Friedel-Crafts alkylation to afford 1,1-diaryl-2-halo-3,3,3-trifluoropropanes [Ar(Ar')CH-CH(X)CF3] in high yields (up to 96%) as a mixture of two diastereomers. The prepared halogenopropanes were easily converted into the corresponding mixtures of E-/Z-trifluoromethylated diarylethenes [Ar(Ar')C═CCF3] (in yields up to 96%) by dehydrohalogenation with base (KOH or t-BuOK). The mechanism of elimination (E2 and Ecb) depends on the nature of the leaving group and reaction conditions.

Generation and reactions of thiocarbonyl S-(2,2,2-trifluoroethanides). Synthesis of trifluoromethylated 1,3-dithiolanes, thiiranes and alkenes

“…The observed regioselectivity confirms the explanation that heteroaromatic substituents promote the formation of diradical intermediates in the course of formal [3+2]-cycloadditions leading to 1,3-dithiolanes [15,18,20]. Fluorinated alkenes are of current interest and the development of new methods for their preparation is a challenging task for modern organic chemistry [14,21]. Some thiiranes described in this study underwent spontanous desulfurization and the corresponding 3,3,3-trifluoropropenes 6a-6c were formed as final products.…”

Reactions of linear conjugated dienone structures with arenes under superelectrophilic activation conditions. An experimental and theoretical study of intermediate multicentered electrophilic species

“…The formation of the product of aryl group exchange 2a was observed for the reaction of compounds 1e and 1 f bearing electron donating aryl groups adjacent to the butadiene system. Similar exchange of aryl groups was previously observed by ourselves in the same reactions of cinnamic acid derivatives 21,22 and trifluoromethyl styrenes 23 with arenes under superelectrophilic activation conditions.…”

Synthesis of α-(Trifluoromethyl)styrenes and 1,3-Di(trifluoromethyl)indanes via Electrophilic Activation of TMS Ethers of (Trifluoromethyl)benzyl Alcohols in Brønsted Acids

“…Hydrolysis of E under the reaction work-up furnishes finally compound 7k . It should be noted that a similar transformation of the CF 2 group into carbonyl one in TfOH with consequent hydrolysis has been observed by us previously …”