Andrej V. Matsnev

Shelf-stable electrophilic trifluoromethylating reagents: A brief historical perspective

Summary Since the discovery by Yagupolskii and co-workers that S-trifluoromethyl diarylsulfonium salts are effective for the trifluoromethylation of thiophenolates, the design and synthesis of electrophilic trifluoromethylating reagents have been extensively researched in both academia and industry, due to the significant unique features that trifluoromethylated compounds have in pharmaceuticals, agricultural chemicals, and functional materials. Several effective reagents have been developed by the groups of Yagupolskii, Umemoto, Shreeve, Adachi, Magnier, Togni and Shibata. Due to the high stability and reactivity of these reagents, a series of Umemoto reagents, Togni reagent and Shibata reagent are now commercially available. In this review, we wish to briefly provide a historical perspective of the development of so-called “shelf-stable electrophilic trifluoromethylating reagents”, although this field is in constant development.

Anti-Selective Aldol Reactions of Pentafluorosulfanylacetic Acid Esters with Aldehydes Mediated by Dicyclohexylchloroborane

Aldol reactions of pentafluorosulfanyl (SF5)-substituted acetic acid esters with both aromatic and aliphatic aldehydes proceeded with excellent anti-diastereoselectivity and good to high yields using dicyclohexylchloroborane/triethylamine. This methodology enabled the synthesis of hitherto unknown α-SF5-β-hydroxy esters. Using a norephedrine-based auxiliary, high asymmetric induction was observed. The stereochemistry of products was assigned by NMR spectroscopy and proved by X-ray diffraction analysis. The intermediate enolate was identified as a highly unstable species.

Ambiphilic properties of SF5CF2CF2Br derived perfluorinated radical in addition reactions across carbon-carbon double bonds.

The extraordinary properties of the pentafluorosulfanyl (SF5) group attract attention of organic chemists. While numerous SF5-substituted compounds have been synthesized, the direct introduction of SF5(CF2)n moieties has remained almost unexplored. Our investigations revealed the ambiphilic character of the SF5CF2CF2 radical. Addition reactions to electron-rich or electron-deficient alkenes profit either from its electrophilic or nucleophilic properties. Thus, the readily available SF5CF2CF2Br proved to be a promising and versatile building block for the introduction of this perfluorinated moiety.

Pentafluorosulfanyldifluoroacetic acid: rebirth of a promising building block.

Three novel, easily scalable routes for the synthesis of pentafluorosulfanyldifluoroacetic acid, SF5CF2C(O)OH, are described. Reactions of its acid chloride with amines and alcohols led to a small library of 15 amides and five esters, respectively. The reaction of the acid chloride with phenylmagnesium bromide gave the corresponding acetophenone. Pentafluorosulfanyldifluoroacetonitrile was obtained from pentafluorosulfanyldifluoroacetamide by dehydration with diphosphorus pentoxide.

Synthesis of SF5CF2-Containing Enones and Instability of This Group in Specific Chemical Environments and Reaction Conditions

The chemistry of the SF5CF2 moiety has been scarcely investigated. In this report, we present synthetic pathways to a variety of SF5CF2-substituted compounds starting from vinyl ethers and SF5CF2C(O)Cl. In specific chemical environments and under particular reaction conditions, the SF5CF2 moiety is unstable in downstream products resulting in the elimination of the SF5(-) anion and its decomposition to SF4 and F(-). Surprisingly, the formed F(-) can attack the intermediate difluorovinyl moiety to form trifluoromethyl substituted products. This appears to happen when an intermediate neighboring group participation involving a double bond is possible. Under slightly different conditions, the reaction stops at the stage of a difluorovinyl compound.

Synthesis and optical activity of difluoro(organylsulfinyl)acetic acids and their esters

Representatives of a new type of optically active sulfur(IV) compound, arylsulfinyldifluoroacetic acids, have been prepared.

Synthesis of α-(Pentafluorosulfanyl)- and α-(Trifluoromethyl)-Substituted Carboxylic Acid Derivatives by Ireland–Claisen Rearrangement

Earlier studies have shown that [3,3]-sigmatropic rearrangements of allyl esters are useful for the construction of fluorine-containing carboxylic acid derivatives. This paper describes the synthesis of 3-aryl-pent-4-enoic acid derivatives bearing either a pentafluorosulfanyl (SF5) or a trifluoromethyl (CF3) substituent in the 2-position by treatment of corresponding SF5- or CF3-acetates of p-substituted cinnamyl alcohols with triethylamine followed by trimethylsilyl triflate (TMSOTf). This Ireland-Claisen rearrangement delivered approximate 1:1 mixtures of syn/anti diastereoisomers due to tiny differences (<0.5 kcal/mol) both in the energy of (Z)/(E)-isomeric ester enolates and in the alternative Zimmerman-Traxler transition states of model compounds as shown by DFT calculations. Acidic reaction conditions have to be avoided since addition of the reagents in opposite sequence (first TMSOTf then Et3N) led to oligomerization of the cinnamyl SF5- and CF3-acetates. Treatment of the corresponding regioisomeric 1-phenyl-prop-2-en-1-yl acetates under the latter conditions resulted in [1,3]-sigmatropic rearrangement and subsequent oligomerization of the intermediately formed cinnamyl esters. When Et3N was added first followed by TMSOTf, no further reaction of the formed ester was detected.

A new one-pot synthesis of difluoro(organylsulfinyl)acetic acid esters

A novel single-step method for the synthesis of esters of difluoro(organylsulfinyl)acetic acids, by reacting aromatic compounds with isopropyl chlorosulfinyldifluoroacetate, was developed. The feasibility of transforming the sulfoxide intermediates into corresponding sulfides and sulfones was demonstrated.

Syn-selective silicon Mukaiyama-type aldol reactions of (pentafluoro-λ6-sulfanyl)acetic acid esters with aldehydes

Aldol reactions belong to the most frequently used C–C bond forming transformations utilized particularly for the construction of complex structures. The selectivity of these reactions depends on the geometry of the intermediate enolates. Here, we have reacted octyl pentafluoro-λ6-sulfanylacetate with substituted benzaldehydes and acetaldehyde under the conditions of the silicon-mediated Mukaiyama aldol reaction. The transformations proceeded with high diastereoselectivity. In case of benzaldehydes with electron-withdrawing substituents in the para-position, syn-α-SF5-β-hydroxyalkanoic acid esters were produced. The reaction was also successful with meta-substituted benzaldehydes and o-fluorobenzaldehyde. In contrast, p-methyl-, p-methoxy-, and p-ethoxybenzaldehydes led selectively to aldol condensation products with (E)-configured double bonds in 30–40% yields. In preliminary experiments with an SF5-substituted acetic acid morpholide and p-nitrobenzaldehyde, a low amount of an aldol product was formed under similar conditions.