Beyond 1,2,3-triazoles: Formation and Applications of Ketemines Derived from Copper Catalyzed Azide Alkyne Cycloaddition

Ketemines represent an interesting class of organic intermediates that has undergone a regrowth as a consequence of recent extensions of copper catalyzed azide alkyne cycloaddition (Cu- AAC) to other synthetic fields. This review summarizes the most recent generation methods of ketimines from CuAAC reaction, highlighting chemical properties focused on the synthesis of cyclic compounds, among others, affording a general outlook towards the development of new biologically active compounds.

Kinetic, Thermodynamic, and Dynamic Control in Normal vs. Cross [2 + 2] Cycloadditions of Ene-Keteniminium Ions: Computational Understanding, Prediction, and Experimental Verification

Almost all reported intramolecular [2 + 2] reactions of ene-keteniminium ions gave normal [2 + 2] products with a fused bicycle framework, but not cross [2 + 2] products with a bicyclo[3.1.1]heptane skeleton, a highly pursued bioisostere in pharmaceutical chemistry. How to rationalize this and design new cross [2 + 2] reactions? Theoretical studies using density functional theory, high-level ab initio single-point energy calculations, and molecular dynamics showed that this [2 + 2] reaction has all three patterns of regiochemical control: the reaction is controlled either kinetically, thermodynamically, or dynamically. A carbocation model of forming endo and exo carbocations has been proposed to rationalize the reaction outcomes, revealing that the tethers (between alkenes and keteniminium ions), substituents (on the alkenes), and alkene configurations in ene-keteniminium ions play critical roles. These understandings were further used to predict that introducing a substituent in the terminal position of alkene with a trans configuration in ene-keteniminium ions can realize the cross [2 + 2] reaction, which is dynamically controlled for alkyl substituents or kinetically controlled for aryl substituents. These and more other predictions were realized experimentally, and many cross [2 + 2] products with a bicyclo[3.1.1]heptane skeleton can be achieved. Both molecular dynamics and new experiments have also been applied to correct a key but misassigned [2 + 2] product reported in the literature, further supporting the insightful mechanisms reported here.

Access to thiazoles via [3 + 2] cycloaddition of 1,2,3-thiadiazoles with isonitriles

The formal [3 + 2] cycloaddition of 1,2,3-thiadiazoles with isonitriles is developed to access structurally diverse 4,5-disubstituted thiazoles, in which the thioketene as a sulfo-2C-synthon is first disclosed.

Copper(I)-Catalyzed Ketenimine Formation/Aza-Claisen Rearrangement Cascade for Stereoselective Synthesis of α-Allylic Amidines

A copper-catalyzed three-component reaction of terminal alkynes, TsN₃, and tertiary allylic amines is developed toward the one-pot synthesis of α-allylic amidines. The product was synthesized on gram scale under 1 mol % of catalyst loading. Transformations of products into alkenyl amine and other nitrogen-containing compounds are demonstrated without any loss of stereochemical information.

Copper-Catalyzed Diversity-Oriented Synthesis (DOS) of 4-Amino-2H-chromen-2-imines: Application of Kemp Elimination toward O-Heterocycles

We report herein a copper-catalyzed sequential multicomponent reaction of benzo[d]isoxazoles with terminal alkynes and sulfonyl azides, which produced divergent 4-amino-2H-chromen-2-imines with excellent chemical selectivity. The reaction tolerated a broad range of functional groups, and released only N₂ as the sole byproduct. The sulfonyl imino group could be removed to give biologically active free 4-amino-2H-chromenone in good yield.

A copper-catalyzed three component reaction of aryl acetylene, sulfonyl azide and enaminone to form iminolactone via 6π electrocyclization

We developed a copper-catalyzed three component reaction of aryl acetylene, enaminone and sulfonyl azide to construct iminolactone via copper-catalyzed alkyne–azide cycloaddition (CuAAC), Michael addition of metalated ketenimine followed by elimination and 6π electrocyclization.

Copper-Catalyzed Sulfonyl Azide-Alkyne Cycloaddition Reactions: Simultaneous Generation and Trapping of Copper-Triazoles and -Ketenimines for the Synthesis of Triazolopyrimidines

First simultaneous generation and utilization of both copper-triazole and -ketenimine intermediates in copper-catalyzed sulfonyl azide-alkyne cycloaddition reactions is achieved for the one-pot synthesis of triazolopyrimidines via a novel copper-catalyzed multicomponent cascade of sulfonyl azides, alkynes, and azirines. Significantly, the reaction proceeds under very mild conditions in good yields.

Ruthenium-Catalyzed Metathesis Cascade Reactions in Natural Products Synthesis

In this account, we provide a brief summary of recent developments in ruthenium-catalyzed metathesis cascade reactions towards the total synthesis of natural products. We also highlight recent progress from our own laboratory regarding the synthesis of securinega alkaloids and humulanolides, which has resulted in the development of novel ruthenium-catalyzed metathesis cascade reactions. Inspired and guided by the pioneering and elegant research conducted in this area, we developed a regio-controlled relay dienyne metathesis cascade reaction and a cyclobutene-promoted RCM/ROM/RCM cascade reaction for the synthesis of securinega alkaloids and humulanolides, respectively.

One-pot synthesis of hydrazono-sulfonamide adducts using Cu(BTC) MOF catalyst and their remarkable AIEE properties: unprecedented copper(ii)-catalyzed generation of ketenimine

One pot & simple operation; short reaction time; no column purification; very less catalyst loading; scalable.

Copper-catalyzed three-component synthesis of 3-aminopyrazoles and 4-iminopyrimidines via β-alkynyl-N-sulfonyl ketenimine intermediates

3-Aminopyrazoles and 4-iminopyrimidines were efficiently prepared via copper-catalyzed three-component reactions of butadiynes, sulfonylazides, and hydrazides or imidamides. The reactions were regioselectively approached via the formation of a β-alkynyl-N-sulfonyl ketenimine intermediate which represented a new and effective 1,3-dielectrophilic equivalent in organic synthesis.

Ynamides in ring forming transformations

The ynamide functional group activates carbon-carbontriple bonds through an attached nitrogen atom that bears an electron-withdrawing group. As a result, the alkyne has both electrophilic and nucleophilic properties. Through the selection of the electron-withdrawing group attached to nitrogen, chemists can modulate the electronic properties and reactivity of ynamides, making these groups versatile synthetic building blocks. The reactions of ynamides also lead directly to nitrogen-containing products, which provides access to important structural motifs found in natural products and molecules of medicinal interest. Therefore, researchers have invested increasing time and research in the chemistry of ynamides in recent years. This Account surveys and assesses new organic transforma-tions involving ynamides developed in our laboratory and in others around the world. We showcase the synthetic power of ynamides for rapid assembly of complex molecular structures. Among the recent reports of ynamide transformations, ring-forming reactions provide a powerful tool for generating molecular complexity quickly. In addition to their synthetic utility, such reactions are mechanistically interesting. Therefore, we focus primarily on the cyclization chemistry of ynamides. This Account highlights ynamide reactions that are useful in the rapid synthesis of cyclic and polycyclic structural manifolds. We discuss the mechanisms active in the ring formations and describe representative examples that demonstrate the scope of these reactions and provide mechanistic insights. In this discussion, we feature examples of ynamide reactions involving radical cyclizations, ring-closing metathesis, transition metal and non-transition metal mediated cyclizations, cycloaddition reactions, and rearrangements. The transformations presented rapidly introduce structural complexity and include nitrogen within or in close proximity to a newly formed ring (or rings). Thus, ynamides have emerged as powerful synthons for nitrogen-containing heterocycles and nitrogen-substituted rings, and we hope this Account will promote continued interest in the chemistry of ynamides.

An intramolecular [2 + 2] cycloaddition of ketenimines via palladium-catalyzed rearrangements of N-allyl-ynamides

A cascade of Pd-catalyzed N-to-C allyl transfer-intramolecular ketenimine-[2 + 2] cycloadditions of N-allyl ynamides is described. This tandem sequence is highly stereoselective and the [2 + 2] cycloaddition could be rendered in a crossed or fused manner depending on alkene substitutions, leading to bridged and fused bicycloimines.