Dual Role of Alkynyl Halides in One-Step Synthesis of Alkynyl Epoxides

Strain-Release Driven Epoxidation and Aziridination of Bicyclo[1.1.0]butanes via Palladium Catalyzed σ-Bond Nucleopalladation

The development of preparative methods for the synthesis of four-membered carbocycles is gaining increasing importance due to the widespread utility of cyclic compounds in medicinal chemistry. Herein, we report the development of a new methodology for the production of spirocyclic epoxides and aziridines containing a cyclobutane motif. In a two-step one-pot process, a bicyclo[1.1.0]butyl sulfoxide is lithiated and added to a ketone, aldehyde or imine, and the resulting intermediate is cross-coupled with an aryl triflate through C-C σ-bond alkoxy- or aminopalladation with concomitant epoxide or aziridine formation. After careful optimization, a remarkably efficient reaction was conceived that tolerated a broad variety of both aromatic and aliphatic substrates. Lastly, through several high yielding ring-opening reactions, we demonstrated the excellent applicability of the products as modular building blocks for the introduction of three-dimensional structures into target molecules.

Strain-Release Driven Epoxidation and Aziridination of Bicyclo[1.1.0]butanes via Palladium Catalyzed σ-Bond Nucleopalladation

The development of preparative methods for the synthesis of four-membered carbocycles is gaining increasing importance due to the widespread utility of cyclic compounds in medicinal chemistry. Herein, we report the development of a new methodology for the production of spirocyclic epoxides and aziridines containing a cyclobutane motif. In a two-step one-pot process, a bicyclo[1.1.0]butyl sulfoxide is lithiated and added to a ketone, aldehyde or imine, and the resulting intermediate is cross-coupled with an aryl triflate through C-C σ-bond alkoxy- or aminopalladation with concomitant epoxide or aziridine formation. After careful optimization, a remarkably efficient reaction was conceived that tolerated a broad variety of both aromatic and aliphatic substrates. Lastly, through several high yielding ring-opening reactions, we demonstrated the excellent applicability of the products as modular building blocks for the introduction of three-dimensional structures into target molecules.

Transition-metal free C-N bond formation from alkyl iodides and diazonium salts via halogen-atom transfer

Construction of C-N bond continues to be one part of the most significant goals in organic chemistry because of the universal applications of amines in pharmaceuticals, materials and agrochemicals. However, E2 elimination through classic SN2 substitution of alkyl halides lead to generation of alkenes as major side-products. Thus, formation of a challenging C(sp3)-N bond especially on tertiary carbon center remains highly desirable. Herein, we present a practical alternative to prepare primary, secondary and tertiary alkyl amines with high efficiency between alkyl iodides and easily accessible diazonium salts. This robust transformation only employs Cs2CO3 promoting halogen-atom transfer (XAT) process under transition-metal-free reaction conditions, thus providing a rapid method to assemble diverse C(sp3)-N bonds. Moreover, diazonium salts served as alkyl radical initiator and amination reagent in the reaction. Mechanism studies suggest this reaction undergo through halogen-atom transfer process to generate active alkyl radical which couples with diazonium cations to furnish final products.

Au-Catalyzed intermolecular (3 + 2 + 1) and (5 + 2) cycloaddition for the synthesis of 1,4-dioxenes and 4,7-dihydrooxepines

1,4-Dioxenes and 4,7-dihydrooxepines present interesting potential as motifs for the incorporation of biologically relevant molecules, agrochemicals and materials. In this study, two efficient intermolecular (3 + 2 + 1) and (5 + 2) cycloadditions for the synthesis of 1,4-dioxenes and 4,7-dihydrooxepines are achieved with gold catalysis.

Transition-Metal-Free One-Pot Synthesis of Naphthoquinonefuran Derivatives Through Sequential Nucleophilic Substitution-Nucleophilic Addition Reaction

A transition-metal-free route for tandem one-pot synthesis of naphthoquinonefuran derivatives from 2-hydroxynaphthoquinones has been developed. The sequentially accomplished process comprises an intermolecular alkynylation of sp²-carbon at the 3 position of 2-hydroxynaphthoquinones with arylethynyl bromides, followed by a base-promoted intramolecular nucleophilic annulation reaction. A broad range of functional groups is compatible with this reaction, and diverse naphtho[2,3-b]furan-4,9-diones can be obtained with good yields and excellent regioselectivity.

Regio- and Stereoselective Synthesis of 1,2-Dihaloalkenes Using In-Situ-Generated ICl, IBr, BrCl, I2, and Br2

We describe a catalyst-free 1,2-trans-dihalogenation of alkynes with an unprecedented substrate scope and exclusive regio- and stereoselectivity. This versatile dihalogenation system-a combination of NX¹S electrophile and alkali metal halide (MX²) in acetic acid-is applicable for diverse categories of alkynes (electron-rich or poor alkynes, internal and terminal alkynes, or heteroatoms such as O-, N-, S-substituted alkynes). The hydrogen bonding donor solvent acetic acid is essential for the in-situ generation of X¹X² electrophile, including ICl, IBr, BrCl, I_2, and Br₂.

Palladium-Catalyzed Decarboxylative Alkynylation of α-Acyloxyketones by C(sp3 )-O Bond Cleavage

Palladium-catalyzed decarboxylative alkynylation of α-acyloxyketones triggered by C(sp³ )-O bond cleavage is disclosed. The decarboxylation strategy featuring a neutral reaction condition enabled an unprecedent catalytic alkynylation of a ketone enolate. The reaction was applied to a variety of substrates, giving desired products in good yields. We successfully obtained X-ray crystallography of a new palladium-enolate intermediate that was synthesized by a reaction of [Pd(cod)(CH₂ TMS)₂ ] with XPhos and α-acyloxyketone at room temperature, indicating facile C(sp³ )-O bond disconnection.

An efficient synthesis of gem-diiodoolefins and (E)-iodoalkenes from propargylic amides with a Cu(i)/Cu(iii) cycle

A copper-catalyzed cyclization/iodination reaction from propargylic amides to access gem-diiodoolefins and (E)-iodoalkenes has been developed.

Haloalkynes: a powerful and versatile building block in organic synthesis

Inspired by the need for green and sustainable chemistry, modern synthetic chemists have been seeking general and practical ways to construct complex molecules while maximizing atom economy and minimizing synthetic steps. Over the past few decades, considerable progress has been made to fulfill these goals by taking advantage of transition metal catalysis and chemical reagents with diverse and tunable reactivities. In recent years, haloalkynes have emerged as powerful and versatile building blocks in a variety of synthetic transformations, which can be generally conceived as a dual functionalized molecules, and different reaction intermediates, such as σ-acetylene-metal, π-acetylene-metal, and halovinylidene-metal complexes, can be achieved and undergo further transformations. Additionally, the halogen moieties can be retained during the reaction processes, which makes the subsequent structural modifications and tandem carbon-carbon or carbon-heteroatom bond formations possible. As a consequence, impressive effort has been devoted to this attractive area, and some elegant work has been done over the past several years. This Account highlights some of the recent progress on the development of efficient and practical synthetic methods involving haloalkyne reagents in our laboratory and in others around the world, which showcase the synthetic power of haloalkynes for rapid assembly of complex molecular structures. The focus is primarily on reaction development with haloalkynes, such as cross-coupling reactions, nucleophilic additions, and cycloaddition reactions. The designed approaches, as well as serendipitous observations, will be discussed with special emphasis placed on the mechanistic aspects and the synthetic utilities of the obtained products. These transformations can lead directly to heteroatom-containing products and introduce structural complexity rapidly, thus providing new strategies and quick access to a wide range of functionalized products including many synthetically useful conjugated cyclic and acyclic structures that have potential applications in natural product synthesis, materials science, and drug discovery. Importantly, most of these protocols allow multiple bond-forming events to occur in a single operation, thereby offering opportunities to advance chemical synthesis and address the increasing demands for economical and sustainable synthetic methods. We anticipate that a deep understanding of the properties of haloalkyne reagents and the underlying working mechanism can lead to the development of novel catalytic systems to answer the unsolved challenges in haloalkyne chemistry, which, in turn, may be also instructive for other research areas. We hope this Account will help to provide a guideline for researchers who are interested in this fertile area.

Alkyne aminohalogenation enabled by DBU-activated N-haloimides: direct synthesis of halogenated enamines

Activated by DBU, N-haloimides can be used as both halogen and nitrogen sources to achieve the difunctionalization of terminal alkynes, giving rise to useful halogenated enamines with high efficiency and high regio- and stereoselectivities. The cascade reaction features simple manipulation, mild conditions, a broad substrate scope, readily available reagents, and atom-economy.

Indium(iii) catalysed regio- and stereoselective hydrothiolation of bromoalkynes

Hydrothiolation of bromoalkynes has been reported for the first time under metal catalysed conditions. Indium(iii) trifluoromethanesulfonate was demonstrated as the first catalyst which can catalyse the hydrothiolation of bromoalkynes with absolute regio- and stereoselectivity to generate synthetically valuable (Z)-β-bromo vinyl sulfides in good yields.

Synthesis of thioamides via one-pot A3-coupling of alkynyl bromides, amines, and sodium sulfide

We herein describe a novel method for the synthesis of thioamides by a three component condensation of alkynyl bromides, amines, and Na₂S·9H₂O.

Facile and efficient synthesis of 1-haloalkynes via DBU-mediated reaction of terminal alkynes and N-haloimides under mild conditions

Directly from terminal alkynes and with N-halosuccinimides (halo = Br and I) or N-cholorophthalimide as the halogen sources, DBU as the activator, 1-haloalkynes were prepared in good to excellent yields at room temperature.

Synthesis of D-abrines by palladium-catalyzed reaction of ortho-iodoanilines with N-Boc-N-methylalanyl-substituted acetaldehyde and acetylene

A novel strategy to N-Boc-N-methyl--tryptophans (abrine derivatives) was developed that relies on the palladium-catalyzed annulation of ortho-iodoanilines 12 with either N-Boc-N-methyl-propargylglycine 16 or aldehyde 11. Both 11 and 16 can be prepared from d-serine. An alternative route to propargylglycine 16 utilizes an enantioselective propargylation reaction of glycine imine 17.

Cu(II)-catalyzed synthesis of naphthalene-1,3-diamine derivatives from haloalkynes and amines

An efficient procedure for the preparation of naphthalene-1,3-diamine derivatives by copper-catalyzed haloalkynes with amines has been reported. The reaction was supposed to proceed through a coupling reaction followed by the dimerization of ynamines.

Facile preparation of indoles and 1,2-benzothiazine 1,1-dioxides: nucleophilic addition of sulfonamides to bromoacetylenes and subsequent palladium-catalyzed cyclization

Bromine as a double agent: The bromine atom in 1-bromo-1-alkynes works as an electron-withdrawing group to effect the nucleophilic addition of sulfonamides. It again plays a pivotal role in the palladium-catalyzed cyclization of the resultant (Z)-2-(sulfonylamino)-1-bromoalkenes into nitrogen heterocycles (see scheme).