Fluorosulfonamide-Directed Heteroarylation of Aliphatic C(sp3)-H Bonds.

Herein, we describe a formal dehydrogenative cross coupling of heterocycles with unactivated aliphatic amines. The resulting transformation enables the direct alkylation of common heterocycles by merging N-F-directed 1,5-HAT with Minisci chemistry, leading to predictable site selectivity. The reaction provides a direct route for the transformation of simple alkyl amines to value-added products under mild reaction conditions, making this an attractive option for C(sp3)-H heteroarylation.

Copper-Catalyzed, N-Directed Csp3-H Trifluoromethylthiolation (-SCF3) and Trifluoromethylselenation (-SeCF3).

A direct and versatile copper-catalyzed trifluoromethylthiolation and trifluoromethylselenation of primary, secondary, and tertiary aliphatic C-H bonds was developed. The reaction provides direct access to molecules containing these emerging moieties in the presence of a wide range of common functional groups and in complex molecular environments.

Fenton-Inspired C-H Functionalization: Peroxide-Directed C-H Thioetherification.

Substoichiometric iron mediates the thioetherification of unactivated aliphatic C-H bonds directed by resident silylperoxides. Upon exposure to a catalytic amount of iron(II) triflate, TIPS-protected peroxides bearing primary, secondary, and tertiary C-H sites undergo chemoselective thioetherification of remote C-H bonds with diaryl disulfides. The reaction demonstrates a broad substrate scope and functional group tolerance without the use of any noble metal additives. Mechanistic experiments suggest that the reaction proceeds through 1,5-H atom abstraction by a hydroxyl radical generated with iron.

1,2-(Bis)trifluoromethylation of Alkynes: A One-Step Reaction to Install an Underutilized Functional Group.

Modifying the electronic properties of olefins is the quintessential approach to tuning alkene reactivity. In this context, the exploration of trifluoromethyl groups as divergent electronic modifiers has not been considered. In this work, we describe a copper-mediated 1,2-(bis)trifluoromethylation of acetylenes to create E-hexafluorobutenes (E-HFBs) under blue light in a single step. The reaction proceeds with high yield and E/Z selectivity. Since the alkyne captures two trifluoromethyl groups from each molecule of bpyCu(CF3 )3 , mechanistic studies were conducted to illuminate the role of the reactants. Interestingly, E-HFBs exhibit remarkable stability to standard olefin functionalization reactions in spite of the pendant trifluoromethyl groups. This finding has significant implications for medicine, agroscience, and materials.

Stereoinversion of Unactivated Alcohols by Tethered Sulfonamides.

The direct, catalytic substitution of unactivated alcohols remains an undeveloped area of organic synthesis. Moreover, catalytic activation of this difficult electrophile with predictable stereo-outcomes presents an even more formidable challenge. Described herein is a simple iron-based catalyst system which provides the mild, direct conversion of secondary and tertiary alcohols to sulfonamides. Starting from enantioenriched alcohols, the intramolecular variant proceeds with stereoinversion to produce enantioenriched 2- and 2,2-subsituted pyrrolidines and indolines, without prior derivatization of the alcohol or solvolytic conditions.

Aqueous Benzylic C-H Trifluoromethylation for Late-Stage Functionalization.

The installation of trifluoromethyl groups has become an essential step across a number of industries such as agrochemicals, drug discovery, and materials. Consequently, the rapid introduction of this critical functional group in a predictable fashion would benefit current practitioners in those fields. This communication describes a mild trifluoromethylation of benzylic C-H bonds with high selectivity for the least hindered hydrogen atom. The reaction provides monotrifluoromethylation and proceeds in an environmentally friendly acetone/water solvent system. The method can be used to install benzylic trifluoromethyl groups on highly functionalized drug molecules.

Manganese-Catalyzed Borylation of Unactivated Alkyl Chlorides.

The use of low-cost manganese(II) bromide (MnBr2) and tetramethylethylenediamine (TMEDA) catalyzes the cross coupling of (bis)pinacolatodiboron with a wide range of alkyl halides, demonstrating the first manganese-catalyzed coupling with alkyl electrophiles. This method allows access to primary, secondary, and tertiary boronic esters from the parent chlorides, which were previously inaccessible as coupling partners. The reaction proceeds in high yield with as little as 1000 ppm catalyst loading, while 5 mol % can provide high yields in as little as 30 min. Finally, radical-clock experiments revealed that at 0 °C direct borylation outcompetes alternative radical processes, thereby providing synthetically useful, temperature-controlled reaction outcomes.

Iron-Catalyzed, Fluoroamide-Directed C-H Fluorination.

This communication describes a mild, amide-directed fluorination of benzylic, allylic, and unactivated C-H bonds mediated by iron. Upon exposure to a catalytic amount of iron(II) triflate (Fe(OTf)2), N-fluoro-2-methylbenzamides undergo chemoselective fluorine transfer to provide the corresponding fluorides in high yield. The reaction demonstrates broad substrate scope and functional group tolerance without the use of any noble metal additives. Mechanistic and computational experiments suggest that the reaction proceeds through short-lived radical intermediates with F-transfer mediated directly by iron.

A unified strategy for iron-catalyzed ortho-alkylation of carboxamides.

Using 8-aminoquinoline-based aryl carboxamides, the direct ortho-alkylation can be achieved in high yields in the presence of an iron source, 1,2-bis(diphenylphosphino)ethane (dppe) and phenylmagnesium bromide. The reactions proceed without overalkylation and provide high levels of regioselectivity. The benzylation reactions can be performed in air with reagent-grade THF, while the alkylation works well with unactivated secondary bromides and iodides in 2-methyltetrahydrofuran. Moreover, the reactions only require 5-10 min.

Iron-catalyzed borylation of alkyl electrophiles.

The use of low-cost iron(III) acetoacetate (Fe(acac)3) and tetramethylethylenediamine (TMEDA) enables the direct cross-coupling of alkyl halides with bis(pinacolato)diboron. This approach allows for the borylation of activated or unactivated primary, secondary, and tertiary bromides. Moreover, even the borylation of benzylic or allylic chlorides, tosylates, and mesylates are possible. The reactions proceed under mild conditions at room temperature and show broad functional-group compatibility and "robustness" as measured by a modified Glorius robustness screen.

Wacker-type oxidation of internal alkenes using Pd(Quinox) and TBHP.

The Pd-catalyzed TBHP-mediated Wacker-type oxidation of internal alkenes is reported. The reaction uses 2-(4,5-dihydro-2-oxazolyl)quinoline (Quinox) as ligand and TBHP(aq) as oxidant to deliver single ketone constitutional isomer products in a predictable fashion from electronically biased olefins. This methodology is showcased through its application on an advanced intermediate in the total synthesis of the antimalarial drug artemisinin.

Metal-free, photoinduced remote C(sp3)-H borylation.

Here, we describe a protocol for the metal-free, photo-induced borylation of unactivated C(sp3)-H bonds distal to an O-oxalate hydroxamic ester functionality. The methodology requires only substrate and bis(catecholato)diboron under light irradiation to effect the desired transformation. A range of linear and cyclic tertiary and secondary borylation products are obtained in good yields and high site-selectivity enabling the late-stage C(sp3)-H borylation of natural product derivatives and drug-like compounds.

Iron-Catalyzed, Directed Benzylic Borylation.

Herein, we describe an iron-catalyzed benzylic C-H borylation reaction. The reaction targets primary and secondary C(sp3)-H bonds to deliver high-value boronic esters under mild conditions with short (7-8 min) reaction times. Functional groups are well tolerated, and complete site selectivity is observed in the presence of multiple benzylic C-H bonds.

A concise synthesis of (+)-artemisinin.

Malaria represents one of the most medically and economically debilitating diseases present in the world today. Fortunately, there exists a highly effective treatment based on the natural product artemisinin. Despite the development of several synthetic approaches to the natural product, a streamlined synthesis that utilizes low-cost chemical inputs has yet to materialize. Here we report an efficient, cost-effective approach to artemisinin. Key to the success of the strategy was the development of mild, complexity-building reaction cascades that allowed the use of readily available, affordable cyclohexenone as the key starting material.

Palladium-catalyzed alkyne insertion/Suzuki reaction of alkyl iodides.

A palladium-catalyzed alkyne insertion/Suzuki reaction with unactivated alkyl iodides is described. Under the reaction conditions, selective migratory insertion of alkynes avoids ß-hydride elimination and provides a facile synthesis of stereodefined, tetrasubstituted olefins. The transformation offers broad substrate scope for both the alkyl iodide and boron nucleophile. Mechanistic studies have revealed inversion of the stereocenter for the carbon bearing the iodide.

Directed Ni-Catalyzed Reductive Arylation of Aliphatic C-H Bonds.

Herein, we describe the nickel-catalyzed reductive arylation of remote C(sp3)-H bonds with aryl electrophiles. The reaction targets secondary and tertiary C(sp3)-H bonds to deliver all-carbon quaternary centers. The success of this method relies on a novel amidyl radical precursor that tolerates reducing conditions, namely O-oxalate hydroxamic acid esters.

Interrupting the Barton-McCombie Reaction: Aqueous Deoxygenative Trifluoromethylation of O-Alkyl Thiocarbonates.

The site-selective trifluoromethylation of aliphatic systems remains an important challenge. This work describes a light-driven, copper-mediated trifluoromethylation of O-alkyl thiocarbonates. The reaction provides broad functional group tolerance (e.g., alkyne, alkene, phenol, free alcohol, electron-rich and -deficient arenes), thereby offering orthogonality and practicality for trifluoromethylation. A radical organometallic mechanism is proposed.

Csp3-H Trifluoromethylation of Unactivated Aliphatic Systems.

A straightforward method for the undirected trifluoromethylation of unactivated methylene units was developed. The reaction proceeds in aqueous acetonitrile with Grushin's reagent, bpyCu(CF3)3, under broad-spectrum white-light irradiation. The trifluoromethylation tolerates a wide range of functional groups including ketones, esters, nitriles, amides, alcohols, and carboxylic acids. The C-H cleavage step is performed via intermolecular H atom abstraction, and the selectivities across a range of methylene units are reported. Mechanistic studies offer a general reaction coordinate for the overall transformation.

Cu-Catalyzed C-N Coupling with Sterically Hindered Partners.

Copper, an earth-abundant metal, has reemerged as a viable alternative to the versatile Pd-catalyzed C-N coupling. Coupling sterically hindered reaction partners, however, remains challenging. Herein, we disclose the discovery and development of a pyrrole-ol ligand to facilitate the coupling of ortho-substituted aryl iodides with sterically hindered amines. The ligand was discovered through a library screening approach and highlights the value of mining heteroatom-rich pharmaceutical libraries for useful ligand motifs. Further evaluation revealed that this ligand is uniquely effective in these challenging transformations. The reaction enables the coupling of sterically hindered primary and secondary amines, anilines, and amides with broad functional group tolerance.