Catalytic Asymmetric Conjugate Addition of Mercaptans to β-Substituted-β-Trifluoromethyl Oxazolidinone Enoates: Access to Chiral Trifluoromethylated Tertiary Thioethers and Thiols

Metal-free synthesis of γ-ketosulfones through Brønsted acid-promoted conjugate addition of sulfinamides

A straightforward and general metal-free method has been developed to add sufinamide-derived sulfone units on Michael acceptors under mild conditions. This reaction enables the preparation of a large variety of original γ-ketosulfones, of which only a few synthetic methods have been reported. The mild reaction conditions used tolerate a wide diversity of functional groups and empower the implementation of a late-stage functionalisation strategy.

NbCl5-catalyzed sulfa-Michael addition for constructing quaternary centers in enones

A novel NbCl5-catalyzed sulfa-conjugate addition has been developed to construct quaternary centers in various enones. This new method enables a range of functionalized thiols to access different β-sulfido carbonyl compounds bearing a quaternary center. 27 novel β-sulfido ketones have been obtained with moderate to excellent yields. The preparative scale reactions also proceed well, showing no decrease in yield. We further studied the mechanism by DFT calculations. This methodology is significant in sulfur chemistry, especially in sulfa-conjugate addition, giving a new pathway to add thiols to tri-substituted enones.

Base-catalyzed diastereodivergent thia-Michael addition to chiral β-trifluoromethyl-α,β-unsaturated N-acylated oxazolidin-2-ones

Base-catalyzed diastereodivergent thia-Michael addition of thiols to chiral β-trifluoromethyl-α,β-unsaturated N-acylated oxazolidin-2-ones is reported. By tuning the base-catalyst (i-Pr2NEt, DABCO, or P2-t-Bu), a range of chiral thia-Michael adducts was synthesized in good yields with high diastereoselectivities. A plausible mechanism was proposed on the basis of the experimental results. This work is complementary to the existing methods offering advantages, e.g., switchable diastereoselectivity using a readily synthesized chiral starting material, a cheap and readily available base catalyst, and a simple and practical operation, enabling synthetic application in organic synthesis.

NBS-mediated elimination of β-keto sulfides to access enones and dienones

A novel transformation of β-keto sulfides into enones has been developed. The new method facilitates an NBS-mediated elimination of sulfides to access both enones and dienones. 22 enone products were obtained in moderate to high yields. 4 different dienones were also prepared in 73%-93% yields. 7 different alkylthio motifs have been removed efficiently from β-keto sulfides. We also found that our transformation proceeds well in gram-scale reactions showing no decrease in yield. This methodology is significant in the research and application of sulfides, giving a new pathway to transform β-keto sulfides into enones.

Copper-Catalyzed 1,2-Trifluoromethylation Carbonylation of Unactivated Alkenes: Efficient Access to β-Trifluoromethylated Aliphatic Carboxylic Acid Derivatives

A novel copper-catalyzed carbonylative trifluoromethylation of unactivated alkenes has been developed. A broad range of β-trifluoromethylated carboxylic acid derivatives were prepared in moderate to excellent yields from simple alkenes with excellent regioselectivity. It is noteworthy that ethylene gas, as the simplest olefin, can also be applied directly to obtain β-trifluoromethylated amides and ester. This transformation presents the first example on carbonylative trifluoromethylation of alkenes.

Iridium-catalyzed enantioselective addition of an N-methyl C-H bond to α-trifluoromethylstyrenes via C-H activation

The Ir-catalyzed enantioselective addition of an N-methyl C-H bond of 2-(methylamino)pyridine derivatives to α-trifluoromethylstyrenes proceeded via C-H activation to give chiral γ-branched amine derivatives having a trifluoromethyl-substituted stereocenter. It was found that a bulky and electron-withdrawing group at the 3-position of 2-(methylamino)pyridines was necessary for the present C-H addition reaction catalyzed by a cationic iridium/chiral bisphosphine complex.

Copper-Catalyzed Enantioselective Formation of C-CF3 Centers from β-CF3 -Substituted Acrylates and Acrylonitriles

The catalytic asymmetric synthesis of β-trifluoromethylated esters or nitriles is reported. The use of an in situ formed chiral Cu-H complex allowed the enantioselective reduction of β-trifluoromethylated acrylates or acrylonitriles. The reaction proceeds smoothly affording the corresponding enantioenriched products in good to excellent yields and outstanding enantioselectivities (up to 98 % ee). The mechanism of the reaction was studied, and a plausible reaction pathway was suggested accordingly. Finally, the versatility of the products was highlighted through functional group manipulations.

Stereoselective organocatalytic sulfa-Michael reactions of aryl substituted α,β-unsaturated N-acyl pyrazoles

A variety of functionalised sulfides has been obtained in good to high stereoselectivity via sulfa-Michael reaction of α,β-unsaturated N-acyl pyrazoles with thiols or thioacetic acid using readily available organocatalysts and working under mild conditions.

Asymmetric FeII-Catalyzed Thia-Michael Addition Reaction to α,β-Unsaturated Oxazolidin-2-one Derivatives

A highly enantioselective Fe^II-catalyzed thia-Michael addition to α,β-unsaturated carbonyl derivatives was developed. The scope of the reaction was demonstrated with a selection of aromatic, heterocyclic and aliphatic thiols, and various Michael acceptors. The corresponding β-thioethers were obtained in good to excellent yields (up to 98%) and moderate to excellent enantioselectivities (up to 96:4 er). Unusual hepta-coordination of the metal and chelation to α,β-unsaturated oxazolidin-2-one derivatives allowed the construction of a coherent model rationalizing the enantioselective event. DFT calculations support the proposed model for observed stereoselectivities.

Highly enantioselective sulfa-Michael addition reactions using N-heterocyclic carbene as a non-covalent organocatalyst

We report the first asymmetric sulfa-Michael addition (SMA) reactions using a chiral N-heterocyclic carbene (NHC) as a non-covalent organocatalyst. We demonstrate that a triazolium salt derived NHC functions as an excellent Brønsted base to promote enantioselective carbon-sulfur bond formation. The reaction is applicable to a wide range of thiols and electrophilic olefins. Notably, quaternary chiral centers bearing both an S atom and a CF3 group were synthesized with excellent asymmetric control. Mechanistic studies suggest that the facial discrimination is likely to be guided by non-covalent interactions: hydrogen bonding and π-π stacking.