Fluorine, which is the most electronegative element and has a small atomic radius, plays a key role in pharmaceutical, agrochemical, and materials sciences. One of the fluoroalkyl groups, the trifluoromethylthio group (CF3S−), has been well-recognized as an important structural motif in the design of lead compounds for new drug discovery because of its high lipophilicity (Hansch lipophilicity parameter π = 1.44) and strong electron-withdrawing properties, which could improve the drug molecule’s cell-membrane permeability and enhance its chemical and metabolic stability. While classic methods for the preparation of trifluoromethylthiolated compounds typically involve halogen–fluorine exchange reactions of polyhalogenomethyl thioethers or trifluoromethylation of sulfur-containing compounds under harsh reaction conditions, an alternative but more attractive strategy is direct trifluoromethylthiolation of the substrate at a late stage by employing an electrophilic trifluoromethylthiolating reagent. Although several electrophilic trifluoromethylthiolating reagents have been reported previously, these reagents either require a strong Lewis acid/Brønsted acid as an activator or suffer from a toxic nature or limited substrate scope. To address these problems, in late 2011 we initiated a project with the aim to develop new, shelf-stable, and highly reactive electrophilic trifluoromethylthiolating reagents that could easily install the trifluoromethylthio group at the desired positions of the drug molecule at a late stage of drug development. Inspired by the broad reactivity of the hypervalent iodine reagent, we initially discovered a highly reactive trifluoromethylthiolating reagent, trifluoromethanesulfenate 1a. Structure–reactivity studies disclosed that the iodine atom of reagent 1a does not play an important role in this reagent’s reactivity. Consequently, a simplified second-generation electrophilic reagent, trifluoromethanesulfenate 1b, was developed. In parallel, we developed another shelf-stable, highly reactive electrophilic reagent with a broad substrate scope, N-trifluoromethylthiosaccharin (2).In this Account, we mainly describe our discovery of these two different types of electrophilic trifluoromethylthiolating reagents, trifluoromethanesulfenates 1a and 1b and N-trifluoromethylthiosaccharin 2. Systematic studies showed that both types of reagents are highly reactive toward a wide range of nucleophiles, yet the substrate scopes of these two different types of reagents are complementary. In particular, reagents 1a and 1b are more reliable in transition-metal-catalyzed reactions such as copper-catalyzed trifluoromethylthiolation of aryl/vinyl/alkylboronic acids and silver-catalyzed decarboxylative trifluoromethylthiolation of aliphatic carboxylic acids as well as in the organocatalytic asymmetric trifluoromethylthiolation of β-keto esters and oxindoles. Reagent 2 is more electrophilic than reagents 1a and 1b and is more efficient for direct trifluoromethylthiolation with nucleophiles such as alcohols, amines, thiols, and electron-rich arenes. The ease in preparation, broad scope, and mild reaction conditions make reagents 1a, 1b, and 2 very attractive as general reagents that allow rapid installation of the trifluoromethylthio group into small molecules.

A highly efficient Rh-catalyzed carbenoid addition to trifluoromethylthioether for the formation of trifluoromethyl-substituted sulfonium ylide is described. The trifluoromethyl-substituted sulfonium ylide can act as an electrophilic trifluoromethylation reagent, as demonstrated by trifluoromethylation of β-ketoesters and aryl iodides.

A highly selective Lewis acid mediated trifluoromethylthio lactonization/lactamization of olefins is described. The reaction was proposed to proceed via a thiiranium ion intermediate, which was further attacked by the carboxylic acid or amide to generate the corresponding trifluoromethylthiolated lactone/lactam.

•Trifluoromethylthiolation of indoles were achieved efficiently.•Catalytic amount of BrØsted acid was used to activate the trifluoromethylthiolating reagent.•Reactions were compatible with a variety of functional groups.A BrØsted acid-catalyzed electrophilic trifluoromethylthiolation of indoles under mild conditions is described. The reaction was insensitive to moisture and oxygen, that should allow for easy handling. In addition, the reaction is compatible with a variety of functional groups.

A family of electrophilic trifluoromethanesulfenates was prepared. Structure–reactivity relationship studies showed that the substituted groups on the aryl ring of the trifluoromethylthiolating reagent did not have an obvious influence on their reactivities. A simplified electrophilic trifluoromethylthiolating reagent 1c was then identified that can react with a wide range of nucleophiles such as Grignard reagents, arylboronic acids, alkynes, indoles, β-ketoesters, oxindoles, and sodium sulfinates under mild reaction conditions. A variety of functional groups were tolerated under these conditions.

The first nickel-catalyzed α-arylation of 2-(polyfluorophenyl) pyridine with zinc enolates of esters or amides via C–F bond activation under neutral conditions is described. A variety of functional groups such as ester, amide, ether, and amine were tolerated. This method provides a simple and useful tool to synthesize fluorinated α-aryl carboxylic acids and α-aryl amides that are important intermediates for drug discovery.

An organocatalytic asymmetric Michael addition of nitroalkanes to trifluoromethylated acrylamides in good yields and with good to excellent diastereoselectivities and excellent enantioselectivities is described. The Michael adducts could be readily transformed into optically pure trifluoromethylated γ-aminobutyric acid 7 in high yields without loss in enantioselectivities.Keywords: asymmetric; fluorine; Michael addition; organocatalyst; trifluoromethyl

The first palladium-catalyzed coupling of 2-pyridyl-polyfluoroarenes and benzoxazole, thiazole, benzothiazole, benzoimidazole, oxazole or oxadiazole via a concurrent C–F/C–H activation is described. Initial mechanistic studies showed that C–F activation of perfluoroarene is likely the rate-limiting step of the catalytic cycle. This protocol provides a useful and operationally simple process to functionalized polyfluoroarenes.

A Cu-mediated ligandless aerobic fluoroalkylation of arylboronic acids under mild conditions is described for the first time. The reaction tolerates a wide range of functional groups, allowing for further transformation. Mechanistic studies suggest that [RfCu] is the active Cu species that forms the desired perfluoroalkylarenes and that [RfCu] is generated from [PhCu] by either an oxidative addition/reductive elimination mechanism or nucleophilic substitution via a halogen “ate” intermediate.

A new class of stable, strongly π-accepting and modular bis(perfluoroalkyl)-phosphine-oxazoline ligands (FOX) as CO mimics was prepared. It was demonstrated that these ligands, when coordinated to palladium catalysts, promote the asymmetric alkylation of monosubstituted allyl substrates with excellent regio- and enantioselectivity. Solid and solution structure analysis of the FOX-ligated Pd-allyl intermediate reveals that the combination of relative steric and strong trans influences presented by the P(CF3)2 moiety gave rise to the excellent selectivity.

A highly efficient and cost-effective method for the preparation of α,β,β-trifluorostyrene (TFS) and its derivatives is described. The method required only 0.2 mol % of Pd(dba)2 and 0.4 mol % of PtBu3 and occurred to full conversion within 2.0 h. With this method, a wide range of arylboronic acids were efficiently incorporated to generate α,β,β-trifluorostyrene derivatives.

A selective palladium-catalyzed Suzuki–Miyaura coupling reaction of polyfluorophenyl oxazolines through ortho C–F activation is described. It was found that reactions with DPPF as the ligand occurred much faster than those with other ligands. A variety of arylboronic acids including challenging functionalized arylboronic acids such as enolizable ketones, aldehyde, cyano, ester, and trifluoromethyl groups were tolerated with the reaction conditions.