Preparation and application of 2-(arylmethoxy)isopinocampheols for the asymmetric aldol reaction of 3,3,3-trifluoropropionates

Temperature- and Reagent-Controlled Complementary Syn- and Anti-Selective Enolboration-Aldolization of Substituted Phenylacetates

In contrast to methyl phenylacetates, methyl arylacetates do not provide syn-aldols in the dicyclohexylboron triflate/triethylamine (Chx₂BOTf/Et₃N)-mediated enolboration-aldolization reaction. However, a combination of a less bulky boron reagent (dibutylboron triflate, n-Bu₂BOTf), a bulky amine (i-Pr₂NEt), and ambient temperature is required to obtain syn-aldols from methyl arylacetates. The corresponding anti-aldol products have been synthesized by the enolboration-aldolization of methyl arylacetates in the presence of Chx₂BOTf/Et₃N at a lower temperature. We report the first example of a complementary syn- and anti-selective enolboration-aldolization of arylacetates.

Stereoselective aldol reactions using pseudo C2 symmetric 1-benzyl-4-(trifluoromethyl)piperidine-2,6-dione

Crossed aldol reactions of the CF₃-containing pseudo C₂ symmetric cyclic imide 3 were carried out by way of the corresponding boron bisenolate to stereoselectively furnish the desired products 4 and this procedure allowed the preferential construction of the diastereomers of the compounds previously obtained from the acyclic counterpart 1.

Cs2CO3-promoted defluorination and functionalization of α-CF3carbonyl compounds in the presence ofN-,O-, and/orS-nucleophiles

A simple, efficient, and mild method for defluorination and functionalization of 3,3,3-trifluoro carbonyl compounds has been developed. In the present method, Cs₂CO₃ can easily convert α-trifluoromethyl esters, amides, and ketones into β,β-S-, O- and/or N-substituted α,β-unsaturated carbonyl compounds in the presence of N-, O-, and S-nucleophiles with moderate to excellent yields, and furthermore, this transformation with α-trifluoromethyl ester and a series of 2-aminophenols can result in benzooxazoles in good yields.

Cs₂CO₃-promoted defluorination and functionalization of α-CF₃ carbonyl compounds.

Direct Catalytic Asymmetric Mannich-Type Reaction of α- and β-Fluorinated Amides

The last two decades have witnessed the emergence of direct enolization protocols providing atom-economical and operationally simple methods to use enolates for stereoselective C-C bond-forming reactions, eliminating the inherent drawback of the preformation of enolates using stoichiometric amounts of reagents. In its infancy, direct enolization relied heavily on the intrinsic acidity of the latent enolates, and the reaction scope was limited to readily enolizable ketones and aldehydes. Recent advances in this field enabled the exploitation of carboxylic acid derivatives for direct enolization, offering expeditious access to synthetically versatile chiral building blocks. Despite the growing demand for enantioenriched fluorine-containing small molecules, α- and β-fluorinated carbonyl compounds have been neglected in direct enolization chemistry because of the competing and dominating defluorination pathway. Herein we present a comprehensive study on direct and highly stereoselective Mannich-type reactions of α- and β-fluorine-functionalized 7-azaindoline amides that rely on a soft Lewis acid/hard Brønsted base cooperative catalytic system to guarantee an efficient enolization while suppressing undesired defluorination. This protocol contributes to provide a series of fluorinated analogs of enantioenriched β-amino acids for medicinal chemistry.

Catalytic generation of α-CF3 enolate: direct catalytic asymmetric Mannich-type reaction of α-CF3 amide

The introduction of the CF3 unit is a common strategy for modifying pharmacokinetic properties and slowing metabolic degradation in medicinal chemistry. A catalytic and enantioselective addition of α-CF3 enolates allows for expeditious access to functionalized chiral building blocks with CF3-containing stereogenicity. To date, α-CF3 enolates have been a less explored class of nucleophiles because of rapid defluorination. The present study reveals that a designed α-CF3 amide enables a direct asymmetric Mannich-type reaction in a cooperative catalytic system.