Efficient and Divergent Synthesis of Medium‐Sized Lactams through Zinc‐Catalyzed Oxidative Cyclization of Indoly Ynamides †

Silver-Catalyzed Cascade Cyclization of Amino-NH-1,2,3-Triazoles with 2-Alkynylbenzaldehydes: An Access to Pentacyclic Fused Triazoles

An operationally simple Ag(I)-catalyzed approach for the synthesis of isoquinoline and quinazoline fused 1,2,3-triazoles was developed by a condensation and amination cyclization cascade of amino-NH-1,2,3-triazoles with 2-alkynylbenzaldehydes involving three new C-N bond formations in one manipulation, in which the group of -NH of the triazole ring serves as a nucleophile to form the quinazoline skeleton. The efficient protocol can be applied to a variety of substrates containing a range of functional groups, delivering novel pentacyclic fused 1,2,3-triazoles in good-to-excellent yields.

Efficient synthesis of tetracyclic γ-lactams via gold-catalyzed oxidative cyclization of alkenyl diynes

An efficient gold-catalyzed cascade cyclization of alkenyl diynes involving alkyne oxidation, carbene-alkyne metathesis and cyclopropanation has been developed, furnishing a series of tetracyclic γ-lactams bearing one quaternary carbon center and...

Metal-free dearomatization reactions of naphthol-ynamides for the divergent and enantioselective synthesis of azaspirocycles

An efficient Brønsted acid (BA) catalyzed intramolecular dearomatization cyclization of naphthol-ynamides has been developed, enabling the practical and divergent synthesis of two azaspirocycles in high yields.

Lewis acid-promoted cyclizations of o-alkyloxyphenyl-substituted ynamides to construct 2-amidobenzofurans

Lewis acid-promoted cyclizations of o-alkyloxyphenyl-substituted ynamides are described for the general construction of medicinally relevant 2-amidobenzofurans. A diverse array of 3-acyl-2-amidobenzofurans could be effectively constructed via a SnCl4-promoted intermolecular cyclization....

Theoretical insights into the mechanism and origin of chemoselectivity in the catalyst- and directing group-dependent oxidative cyclization of diynes with pyridine N-oxides

The mechanisms and origin of the chemoselectivity of Cu(i)- and Au(i)-catalyzed oxidation of diynes for the divergent syntheses of two different N-heterocycles, substituted pyrroles and dihydroindeno[1,2-c]pyrrol-3(2H)-ones, were elucidated using density functional theory.

Copper-Catalyzed Si-H Bond Insertion Reaction of N-Propargyl Ynamides with Hydrosilanes

Transition-metal-catalyzed Si-H bond insertion reactions are generally limited to stabilized diazo compounds. An efficient copper-catalyzed Si-H bond insertion reaction of N-propargyl ynamides with hydrosilanes is described, allowing practical and atom-economic construction of valuable organosilanes in generally moderate to excellent yields under mild reaction conditions. Notably, this reaction constitutes a new method of Si-H bond insertion reaction involving vinyl cations as key intermediates.

Copper-Catalyzed Cyclization of N-Propargyl Ynamides with Borane Adducts through B-H Bond Insertion

An efficient copper-catalyzed cyclization of N-propargyl ynamides with borane adducts through B-H bond insertion has been developed. A series of valuable organoboron compounds are constructed in generally good yields with a wide substrate scope and good functional group tolerance under mild reaction conditions. Importantly, this protocol via vinyl cation intermediates constitutes a novel way of B-H bond insertion.

Access to Indole-Annulated Medium-Sized Lactams through Protonation/Deuteration-Induced Ring-Opening of Spiroindolines

A protocol has been developed to access indole-annulated eight- and nine-membered lactams through protonation-induced ring-opening of spiroindolines, which are dearomative Heck products of tetrahydro-β-carbolines or hexahydroazepino[3,4-b]indoles. Brønsted acids and nucleophiles were explored and compared in the transformation. A combination of deuterated hydrochloride and deuterated methanol enables deuterative ring-opening of spiroindolines to afford medium-sized lactam diastereoisomers with a deuterium content ratio around 1:1.

Recent Progress in Enolonium Chemistry under Metal-Free Conditions

Umpolung approach through inversion of the polarity of conventional enolates, has opened up an unprecedented opportunity in the cross-coupling via alkylation. The enolonium equivalents can be accessed either by hypervalent iodine reagents, activation/oxidation of amides, or the oxidation of alkynes. Under umpolung conditions, highly basic conditions required for classical enolate chemistry can be avoided, and they can couple with unmodified nucleophiles such as heteroatom donors and electron-rich arenes.

Asymmetric synthesis with ynamides: unique reaction control, chemical diversity and applications

Ynamides are among the most powerful building blocks in organic synthesis and have become invaluable starting materials for the construction of multifunctional compounds and challenging architectures that would be difficult to prepare otherwise. The rapidly growing popularity originates from the unique reactivity and ease of manipulation of the polarized ynamide triple bond, the advance of practical methods for making them, and the simplicity of storage and handling. These attractive features and the demonstration of numerous synthetic applications have spurred the development of intriguing asymmetric reaction strategies during the last decade. An impressive variety of chemo-, regio- and stereoselective carbon-carbon and carbon-heteroatom bond forming reactions with ynamides have been developed and now significantly enrich the toolbox of synthetic chemists. This review provides a comprehensive overview of asymmetric ynamide chemistry since 2010 with a focus on the general scope, current limitations, stereochemical reaction control and mechanistic aspects.

Transition Metal-Catalyzed Tandem Reactions of Ynamides for Divergent N-Heterocycle Synthesis

ConspectusYnamides are electron-rich heteroatom-substituted alkynes with a C-C triple bond directly attached to the amide group. Importantly, this amide group is able to impose an electronic bias, thus resulting in the highly regioselective attack of this polarized alkyne by a large variety of nucleophiles. Over the past two decades, catalytic reactions of ynamides have experienced dramatic developments, especially those catalyzed by transition metals. As a result, ynamides have been widely applied to the rapid and efficient assembly of versatile structurally complex N-containing molecules, especially in an atom-economic and stereoselective way.On the basis of newly developed ynamide preparations and new alkyne transformations, we first developed oxidation-initiated tandem reactions of ynamides such as zinc-catalyzed ynamide oxidation/C-H functionalization and copper-catalyzed ynamide oxidation/carbene metathesis, leading to divergent synthesis of isoquinolones, β-carbolines, and pyrrolo[3,4-c]quinolin-1-ones. Importantly, this protocol represents the first non-noble-metal-catalyzed intermolecular oxidation of alkynes by N-oxide type oxidants, and the related overoxidation could be dramatically inhibited in this non-noble-metal catalysis. Then, we achieved gold-catalyzed amination-initiated tandem reactions of ynamides via α-imino gold carbenes for efficient construction of various 2-aminoindoles, 3-amino-β-carbolines, and 2-aminopyrroles, where two new types of nitrene transfer reagents (benzyl azides and isoxazoles) were discovered. In particular, the use of isoxazoles as nitrene transfer reagents for atom-economic generation of α-imino metal carbenes has also been elegantly exploited by Hashmi, Liu, and many other groups, providing ready access to a wide range of functionalized N-heterocycles. Moreover, we revealed that donor/donor copper carbenes could be generated via copper-catalyzed diyne cyclization under mild conditions. These novel copper carbenes could undergo asymmetric C-H insertion, cyclopropanation, and formal [3 + 2] cycloaddition to produce diverse chiral polycyclic pyrroles with good to excellent enantioselectivities. Thus, this strategy may open new avenues in catalytic asymmetric reaction of ynamides, which remain largely unexplored and deserve more attention. Meanwhile, we also accomplished the efficient and practical synthesis of medium-sized lactams by yttrium-catalyzed cascade cyclization of allyl alcohol-tethered ynamides and the combination of radical chemistry based on visible-light photoredox catalysis with ynamide chemistry for divergent synthesis of useful 2-benzhydrylindoles and 3-benzhydrylisoquinolines.In this Account, we describe a panoramic picture of our recent contributions since 2015 to the development and application of ynamide chemistry in organic synthesis via transition metal-catalyzed tandem reactions by focusing on the tetrafunctionalization of ynamides. These studies provide not only efficient and attractive methods for divergent synthesis of valuable N-heterocycles but also some new insights into the exploration of alkyne chemistry and metal carbene chemistry.

Nitrene Transfer and Carbene Transfer in Gold Catalysis

Catalytic transformations involving metal carbenes are considered one of the most important aspects of homogeneous transition metal catalysis. Recently, gold-catalyzed generation of gold carbenes from readily available alkynes represents a significant advance in metal carbene chemistry. This Review summarizes the advances in the gold-catalyzed nitrene-transfer reactions of alkynes with nitrogen-transfer reagents, such as azides, nitrogen ylides, isoxazoles, and anthranils, and gold-catalyzed carbene-transfer reactions, involving oxygen atom-transfer reactions of alkynes with nitro compounds, nitrones, sulfoxides, and pyridine N-oxides, through the presumable α-imino gold carbene and α-oxo gold carbene intermediates, respectively. Gold-catalyzed processes are reviewed by highlighting their product diversity, selectivity, and applicability, and the mechanistic rationale is presented where possible.