ChemInform Abstract: PbBr2/Al‐Promoted Reductive Addition of 1,1,1‐Trichloro‐2,2,2‐trifluoroethane (Flon) to Aldehydes.

Tanaka, Hideo; Yamashita, S.; Katayama, Y.; Torii, Sigeru

doi:10.1002/chin.198727101

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“…Fujita and Hiyama were able to generate a thermally stable CF 3 CCl 2 ZnCl from CCl 3 CF 3 and Zn powder. At room temperature, addition of CF 3 CCl 2 ZnCl and CF 3 CCl 2 PbCl with various aldehydes and ketones afforded adducts in high yields (Scheme ).…”

Section: Introductionmentioning

confidence: 99%

α-Trifluoromethylated Carbanion Synthons

2008

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Trifluomethylated organic compounds often have properties that make them suitable for diverse applications, including materials science, agrochemistry, and pharmaceutical industry. But of all the therapeutic drugs currently available, about 10% of them have a partially fluorinated moiety. Thus, a great deal of attention is being paid to the development of reliable methodologies for trifluoromethylation. Introduction of a trifluoromethyl group into the target molecules mostly relies on either trifluoromethylating reagents or trifluoromethylated synthetic blocks. The chemistry of trifluoromethyl carbanions, nucleophilic trifluoromethylating agents such as the Ruppert-Prakash reagent, and organometallic species has been intensively developed for their important synthetic applications. But the chemistry of beta,beta,beta-trifluoroethyl carbanions (alpha-trifluoromethyl carbanions) and organometallic species has remained undeveloped despite their potential usefulness in organic synthesis. The issue needs to be addressed. This Account outlines successful alkylations and useful synthetic applications of alpha-trifluoromethyl carbanions, such as alpha-substituted beta,beta,beta-trifluoroethyl, alpha-trifluoromethylethenyl, trifluoroacetimidoyl, alpha-trifluoromethyloxiranyl, and related alpha-trifluoromethylated carbanions. The strong electron-withdrawing effect of the alpha-trifluoromethyl group may stabilize the carbanion species electronically. But alpha-trifluoromethyl carbanions and their corresponding organometallic species mostly release fluoride spontaneously to produce difluoroalkenes. This notorious decomposition of alpha-trifluoromethylated carbanions and anionoids has hindered the development of these species for organic synthesis. A well-designed device for the generation, stabilization, and acceleration for alkylation of the alpha-trifluoromethylated carbanions is needed for their synthetic application, as well as stabilization by the electron-withdrawing alpha-substituent. The reported alpha-substituted alpha-trifluoromethyl carbanions can be roughly categorized into three classes based on their structures. The first category, A, is pi-conjugation-stabilized carbanions, which are stabilized by ester, nitro, sulfone, carbonyl, or phenyl groups. alpha-Substituents of these carbanions can delocalize the negative charges on their pi-system with large sigma R electron-withdrawing effects; this prevents accumulation of negative charge on the fluorine atoms. The second category, B, consists of carbanions with sp(3) orbitals either of highly halogenated carbanionsexamples include pentafluoroethyl(trimethyl)fluorosilicate, pentafluoroethyllithium, and alpha,alpha-dichloro-beta,beta,beta-trifluoroethylzinc speciesor of cyclic structures such as oxiranyl- and aziridinyllithiums. Both of these carbanions are also stabilized since they reduce molecular orbital (MO) overlapping of the carbanion orbital to C-F bond orbitals. The third category, C, has carbanions with their anion center at the sp(2) orbital, such as alpha...

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Section: Introductionmentioning

confidence: 99%