Transition-Metal-Free ipso-Trifluoromethylthiolation of Lithium Aryl Boronates

Simultaneous Stereoinvertive and Stereoselective C(sp3)-C(sp3) Cross-Coupling of Boronic Esters and Allylic Carbonates

With increasing interest in constructing more three-dimensional entities, there has been growing interest in cross-coupling reactions that forge C(sp3)-C(sp3) bonds, which leads to additional challenges as it is not just a more difficult bond to construct but issues of stereocontrol also arise. Herein, we report the stereocontrolled cross-coupling of enantioenriched boronic esters with racemic allylic carbonates enabled by iridium catalysis, leading to the formation of C(sp3)-C(sp3) bonds with single or vicinal stereogenic centers. The method shows broad substrate scope, enabling primary, secondary, and even tertiary boronic esters to be employed, and can be used to prepare any of the four possible stereoisomers of a coupled product with vicinal chiral centers. The new method, which combines the simultaneous enantiospecific reaction of a chiral nucleophile with the enantioselective reaction of a chiral electrophile in a single process, offers a solution for stereodivergent cross-coupling of two C(sp3) fragments.

A Toolbox of Reagents for Trifluoromethylthiolation: From Serendipitous Findings to Rational Design

Two types of electrophilic trifluoromethylthiolating reagents were developed in the past 10 years in our laboratory. The development of the first type of reagent, trifluoromethanesulfenate I, which is highly reactive toward a variety of nucleophiles, was based on an unexpected discovery in the initial design for the development of an electrophilic trifluoromethylthiolating reagent with a hypervalent iodine skeleton. A structure-activity study disclosed that α-cumyl trifluoromethanesulfenate (reagent II) without the iodo substituent is equally effective. Subsequent derivatization let us develop an α-cumyl bromodifluoromethanesulfenate III that could be used for the preparation of [¹⁸F]ArSCF₃. To remediate the low reactivity of the type I electrophilic trifluoromethylthiolating reagent for Friedel-Crafts trifluoromethylthiolation of electron-rich (hetero)arenes, we designed and prepared N-trifluoromethylthiosaccharin IV, which exhibits broad reactivity toward various nucleophiles, including electron-rich arenes. A comparison of the structure of N-trifluoromethylthiosaccharin IV with that of N-trifluoromethylthiophthalimide showed that the replacement of one carbonyl group in N-trifluoromethylthiophthalimide with a sulfonyl group made N-trifluoromethylthiosaccharin IV much more electrophilic. Thus, the replacement of both carbonyls with two sulfonyl groups would further increase the electrophilicity. Such a rationale prompted us to design and develop the current most electrophilic trifluoromethylthiolating reagent, N-trifluoromethylthiodibenzenesulfonimide V, and its reactivity was much higher than that of N-trifluoromethylthiosaccharin IV. We further developed an optically pure electrophilic trifluoromethylthiolating reagent, (1S)-(-)-N-trifluoromethylthio-2,10-camphorsultam VI, for the preparation of optically active trifluoromethylthio-substituted carbon stereogenic centers. Reagents I-VI now constitute a powerful toolbox for the introduction of the trifluoromethylthio group into the target molecules.

Dynamic kinetic asymmetric arylation and alkenylation of ketones

Despite the importance of enantioenriched alcohols in medicinal chemistry, total synthesis, and materials science, the efficient and selective construction of enantioenriched tertiary alcohols bearing two contiguous stereocenters has remained a substantial challenge. We report a platform for their preparation through the enantioconvergent, nickel-catalyzed addition of organoboronates to racemic, nonactivated ketones. We prepared several important classes of α,β-chiral tertiary alcohols in a single step with high levels of diastereo- and enantioselectivity through a dynamic kinetic asymmetric addition of aryl and alkenyl nucleophiles. We applied this protocol to modify several profen drugs and to rapidly synthesize biologically relevant molecules. We expect this nickel-catalyzed, base-free ketone racemization process to be a widely applicable strategy for the development of dynamic kinetic processes.

Visible-light-promoted S-trifluoromethylation of thiophenols with trifluoromethyl phenyl sulfone

Trifluoromethyl phenyl sulfone is traditionally a nucleophilic trifluoromethylating agent. Herein, we report the first example of the use of trifluoromethyl phenyl sulfone as a trifluoromethyl radical precursor. Arylthiolate anions can form electron donor-acceptor (EDA) complexes with trifluoromethyl phenyl sulfone, which can undergo an intramolecular single electron transfer (SET) reaction under visible light irradiation, thus realizing the S-trifluoromethylation of thiophenols under photoredox catalyst-free conditions. Similar S-perfluoroethylation and S-perfluoro-iso-propylation of thiophenols are also achieved using the corresponding perfluoroalkyl phenyl sulfones.

Palladium-Catalyzed Suzuki-Miyaura Cross-Coupling of Oxygen-Substituted Allylboronates with Aryl/Vinyl (Pseudo)Halides

An efficient palladium-catalyzed Suzuki-Miyaura cross-coupling reaction of oxygen atom-substituted allylboronates with aryl/vinyl bromides, iodides, and triflates has been developed. The present coupling reactions proceeded smoothly to provide a variety of allylic siloxanes with high efficiency and excellent regioselectivity. This protocol features broad substrate scope, excellent functional group tolerance, and easy gram-scale preparation, and offers an alternative approach for the synthesis of allylic alcohols and their derivatives.

Asymmetric hydrogenation of trifluoromethyl ketones: application in the synthesis of Odanacatib and LX-1031

The asymmetric hydrogenation of trifluoromethyl ketones via iridium catalysis to access chiral secondary 2,2,2-trifluoroethanols is presented. The key intermediates of Odanacatib and LX1301 were prepared with high yields and enantioselectivities.

Synthetic developments on the preparation of sulfides from thiol-free reagents

This critical review covers the main thiolating reagents with respect to their characteristics and reactivities. In fact, they are complementary to each other and bring different thiolation strategies, avoiding the hazardous thiol derivatives.

Perfluoroalkylation of Thiosulfonates: Synthesis of Perfluoroalkyl Sulfides

A practical synthesis of perfluoroalkyl sulfides is described. The method employs stable and readily accessible thiosulfonates as new electrophiles with commercial nucleophilic perfluoroalkylating reagents. The mild reaction conditions allow access to a wide variety of both aryl- and alkyl-substituted perfluoroalkyl sulfides amenable to pharmaceutical development. Furthermore, the reaction operation is straightforward, odorless, does not produce toxic wastes, and, therefore should appeal to practitioners in industrial-scale productions.

Construction of unique SCF3-containing building blocks via allylic alkylation of Morita-Baylis-Hillman adducts

Lewis base-catalyzed allylic alkylation of Morita-Baylis-Hillman adducts with α-SCF3 ketones has been demonstrated. The developed strategy provides efficient access to a series of highly functionalized scaffolds featuring trifluoromethanesufinyl motif on a stereogenic carbon.