α-Aminocarbene-Mediated Si-H Insertion: Deoxygenative Silylation of Aromatic Amides with Silanes

Gold-Catalyzed Synthesis of 5H-Benzo[b]indeno[2,1-d]silines by Insertion of Vinyl Carbocations into the Si-H Bond

We have developed a gold-catalyzed cascade reaction of aryldiynes bearing a hydrosilyl group to afford a variety of unexplored 5H-benzo[b]indeno[2,1-d]silines. The reaction system is applicable to the synthesis of bidirectionally π-extended silacycles from tetra(alkynyl)aryl compounds. Computational studies suggest that 5H-benzo[b]indeno[2,1-d]silines are formed via the insertion of a vinyl carbocation intermediate into the Si-H bond.

Deoxygenative Geminal Silylboration of Amides Using Silylboronates: Synthesis and Use of α-Boryl-α-Silylalkylamines

α-Silylalkylamines and α-borylalkylamines are versatile synthetic intermediates and attractive scaffolds found in pharmaceutical drugs and agrochemicals. Despite great progress on synthetic methods for preparation of α-silylalkylamines or α-borylalkylamines, there are no general strategies for preparation of α-boryl-α-silylalkylamines and the reactivity has not been explored. Here we report deoxygenative geminal silylboration of amides using silylboronates in the presence of alkoxide base catalyst, producing α-boryl-α-silylalkylamines. The silicon and boron groups in α-boryl-α-silylalkylamines are found to be utilized to chemoselective transformations, such as protonation and alkylation. This protocol serves various α-silylalkylamines and α-borylalkylamines from readily available amides.

Samarium diiodide/samarium-mediated direct deoxygenative hydroborylation of ketones with hydroborane esters

A direct deoxygenative hydroborylation of ketones with hydroborane ester promoted by a combination of samarium diiodide, samarium and nickel has been developed. In this method, secondary alkyl borate esters are synthesized from unactivated ketones with hydroborane esters in one step. A broad substrate scope and excellent selectivity toward CO cleavage has been demonstrated. This approach represents a general method for the construction of versatile secondary alkyl borate esters from unactivated ketones.

Deoxygenative alkynylation of amides via CO bond cleavage

A novel deoxygenative alkynylation of amides promoted by a synergistic action of a divalent rare-earth element and a transition metal has been developed. In this method, α-alkynyl substituted amines are synthesized from unactivated amides and alkynes in a single transformation. Broad substrate scope and excellent selectivity for CO cleavage has been demonstrated. This approach represents a general method for the construction of versatile α-alkynyl substituted amines from unactivated amide bonds.

Making Full Use of TMSCF3: Deoxygenative Trifluoromethylation/Silylation of Amides

As one of the most powerful trifluoromethylation reagents, (trifluoromethyl)trimethylsilane (TMSCF3) has been widely used for the synthesis of fluorine-containing molecules. However, to the best of our knowledge, the simultaneous incorporation of both TMS- and CF3- groups of this reagent onto the same carbon of the products has not been realized. Herein, we report an unprecedented SmI2/Sm promoted deoxygenative difunctionalization of amides with TMSCF3, in which both silyl and trifluoromethyl groups are incorporated into the final product, yielding α-silyl-α-trifluoromethyl amines with high efficiency. Notably, the silyl group could be further transformed into other functional groups, providing a new method for the synthesis of α-quaternary α-CF3-amines.

Copper/Chiral Phosphoric-Acid-Catalyzed Intramolecular Reductive Isocyanide-Alkene (1 + 2) Cycloaddition: Enantioselective Construction of 2-Azabicyclo[3.1.0]hexanes

Enantioenriched 2-azabicyclo[3.1.0]hexanes are accessed from readily available allyl substituted α-isocyanoesters by intramolecular (1 + 2) cycloaddition with the olefinic moiety and isocyano carbon as the respective C2 and C1 units. Cyclopropanation is initiated by 1,1-hydrocupration of isocyanide followed by formimidoylcopper to copper α-aminocarbenoid equilibration and subsequent (1 + 2) cycloaddition. The unprecedented copper/chiral phosphoric acid (CPA) catalytic system can be operated in the presence of water under air, delivering a variety of 2-azabicyclo[3.1.0]hexanes containing an angular all-carbon quaternary stereocenter in good to excellent yields and enantioselectivity.

Asymmetric Deoxygenative Functionalization of Secondary Amides with Vinylpyridines Enabled by a Triple Iridium-Photoredox-Chiral Phosphoric Acid System

An enantioselective deoxygenative functionalization of secondary amides with vinylpridines is developed by merging relay iridium catalysis and cooperative photoredox-chiral Brønsted acid catalysis, affording a series of valuable chiral amines in moderate to good yields with good enantioselectivities. The intriguing multiple catalytic system invoking triple-catalysis was found to be the key to the success of the current reactions, which may stimulate further development of catalytic methodologies for asymmetric deoxygenative transformations of amides.