Asymmetric Fluorination of Enolates with Nonracemic N-Fluoro-2,10-Camphorsultams

N-Fluoro Ammonium Salts of Cinchona Alkaloids in Enantioselective Electrophilic Fluorination

From 2000, our two research groups independently and simultaneously designed and developed a novel family of electrophilic fluorinating reagents based on the use of Cinchona alkaloids. The chiral N-fluoro ammonium salts demonstrated the highest efficiency compared to prior art in enantioselective electrophilic fluorination for a wide range of substrates. In this account, we tell our respective stories, how the same idea germinated in our laboratories, the characterization of the chiral reagents, the use in stoichiometric quantity then the development of a catalytic version, the application to the synthesis of chiral fluorinated molecules of pharmaceutical interest, and finally the exploitation of our reagents by other teams and for other applications.

Recent Advances in Enantioselective Pd-Catalyzed Allylic Substitution: From Design to Applications

This Review compiles the evolution, mechanistic understanding, and more recent advances in enantioselective Pd-catalyzed allylic substitution and decarboxylative and oxidative allylic substitutions. For each reaction, the catalytic data, as well as examples of their application to the synthesis of more complex molecules, are collected. Sections in which we discuss key mechanistic aspects for high selectivity and a comparison with other metals (with advantages and disadvantages) are also included. For Pd-catalyzed asymmetric allylic substitution, the catalytic data are grouped according to the type of nucleophile employed. Because of the prominent position of the use of stabilized carbon nucleophiles and heteronucleophiles, many chiral ligands have been developed. To better compare the results, they are presented grouped by ligand types. Pd-catalyzed asymmetric decarboxylative reactions are mainly promoted by PHOX or Trost ligands, which justifies organizing this section in chronological order. For asymmetric oxidative allylic substitution the results are grouped according to the type of nucleophile used.

Modern Approaches for Asymmetric Construction of Carbon-Fluorine Quaternary Stereogenic Centers: Synthetic Challenges and Pharmaceutical Needs

New methods for preparation of tailor-made fluorine-containing compounds are in extremely high demand in nearly every sector of chemical industry. The asymmetric construction of quaternary C-F stereogenic centers is the most synthetically challenging and, consequently, the least developed area of research. As a reflection of this apparent methodological deficit, pharmaceutical drugs featuring C-F stereogenic centers constitute less than 1% of all fluorine-containing medicines currently on the market or in clinical development. Here we provide a comprehensive review of current research activity in this area, including such general directions as asymmetric electrophilic fluorination via organocatalytic and transition-metal catalyzed reactions, asymmetric elaboration of fluorine-containing substrates via alkylations, Mannich, Michael, and aldol additions, cross-coupling reactions, and biocatalytic approaches.

(1S)-(−)-N-Trifluoromethylthio-2,10-camphorsultam and its derivatives: easily available, optically pure reagents for asymmetric trifluoromethylthiolation

Optically pure reagents that are able to deliver a trifluoromethylthio group with good to excellent enantioselectivities.

Designing fluorinated cinchona alkaloids for enantioselective catalysis: controlling internal rotation by a fluorine-ammonium ion gauche effect (φ(NCCF))

The C9 position of cinchona alkaloids functions as a molecular hinge, with internal rotations around the C8-C9 (τ(1)) and C9-C4' (τ(2)) bonds giving rise to four low energy conformers (1; anti-closed, anti-open, syn-closed, and syn-open). By substituting the C9 carbinol centre by a configurationally defined fluorine substituent, a fluorine-ammonium ion gauche effect (σ(C-H) → σ(C-F)*; F(δ-)⋅⋅⋅N(+)) encodes for two out of the four possible conformers (2). This constitutes a partial solution to the long-standing problem of governing internal rotations in cinchonium-based catalysts relying solely on a fluorine conformational effect.

Development of the titanium-TADDOLate-catalyzed asymmetric fluorination of β-ketoesters

Titanium-based Lewis acids catalyze the α-fluorination of β-ketoesters by electrophilic N–F-fluorinating reagents. Asymmetric catalysis with TADDOLato–titanium(IV) dichloride (TADDOL = α,α,α',α'-tetraaryl-(1,3-dioxolane-4,5-diyl)-dimethanol) Lewis acids produces enantiomerically enriched α-fluorinated β-ketoesters in up to 91% enantiomeric excess, with either F–TEDA (1-chloromethyl-4-fluoro-1,4-diazoniabicyclo[2.2.2]octane bis(tetrafluoroborate)) in acetonitrile solution or NFSI (N-fluorobenzenesulfonimide) in dichloromethane solution as fluorinating reagents. The effects of various reaction parameters and of the TADDOL ligand structure on the catalytic activity and enantioselectivity were investigated. The absolute configuration of several fluorination products was assigned through correlation. Evidence for ionization of the catalyst complex by chloride dissociation, followed by generation of titanium β-ketoenolates as key reaction intermediates, was obtained. Based on the experimental findings, a general mechanistic sketch and a steric model of induction are proposed.

Transition metal-catalyzed decarboxylative allylation and benzylation reactions

A review. Transition metal catalyzed decarboxylative allylations, benzylations, and interceptive allylations are reviewed.

Organocatalyzed highly enantioselective direct aldol reactions of aldehydes with hydroxyacetone and fluoroacetone in aqueous media: the use of water to control regioselectivity

An organocatalyst prepared from (2R,3R)-diethyl 2-amino-3-hydroxysuccinate and L-proline exhibited high regio- and enantioselectivities for the direct aldol reactions of hydroxyacetone and fluoroacetone with aldehydes in aqueous media. It was found that water could be used to control the regioselectivity. The presence of 20-30 mol% of the catalyst afforded the direct aldol reactions of a wide range of aldehydes with hydroxyacetone to give the otherwise disfavored products with excellent enantioselectivities, ranging from 91 to 99% ee, and high regioselectivities. Aldolizations of fluoroacetone with aldehydes mediated by 30 mol% of the organocatalyst in aqueous media preferentially occurred at the methyl group, yielding products with high enantioselectivities (up to 91% ee); however, these additions took place dominantly at the fluoromethyl group in THF. Optically active 3,5-disubstituted tetrahydrofurans and (2S,4R)-dihydroxy-4-biphenylbutyric acid were prepared by starting from the aldol reaction of hydroxyacetone. Theoretical studies on the role of water in controlling the regioselectivity revealed that the hydrogen bonds formed between the amide oxygen of proline amide, the hydroxy of hydroxyacetone, and water are responsible for the regioselectivity by microsolvation with explicit one water molecule as a hydrogen-bond donor and/or an acceptor.

Adventures in Sulfur−Nitrogen Chemistry

This account reviews our efforts over the past 37 years to understand the chemistry of a select group of sulfur-nitrogen compounds including sulfinimines (N-sulfinyl imines) and N-sulfonyloxaziridines. Our early exploration of the thermal properties of sulfenamides, a class of sulfur-nitrogen compounds about which little was known, resulted in a new procedure, the silver-assisted method, for the construction of sulfenimines (N-sulfenyl imines). Selective oxidations of these compounds resulted in the production of N-sulfinyl imines (sulfinimines) and N-sulfonyloxaziridines. N-Sulfonyloxaziridines turned out to be a new class of aprotic neutral oxidizing reagents. Enantiomerically pure examples afford high ee values in the oxidation of enolates to alpha-hydroxy carbonyl compounds and in the oxidation of sulfides and selenides to sulfoxides and selenoxides. Additions of organometallic reagents to enantiomerically pure sulfinimines provide the best and most versatile method for the asymmetric construction of the carbon-nitrogen stereocenters found in many biologically active compounds. Sulfinimine-derived chiral building blocks provide efficient access to many classes of nitrogen heterocycles including aziridines, 2H-azirines, pyrrolidines, and piperidines.