N-Bromoimide/DBU Combination as a New Strategy for Intermolecular Allylic Amination

Intermolecular Aza-Wacker Coupling of Alkenes with Azoles by Photo-Aerobic Selenium-π-Acid Multicatalysis

Herein, the intermolecular, photoaerobic aza-Wacker coupling of azoles with alkenes by means of dual and ternary selenium-π-acid multicatalysis is presented. The title method permits an expedited avenue toward a broad scope of N-allylated azoles and representative azinones under mild conditions with broad functional group tolerance, as is showcased in more than 60 examples including late-stage drug derivatizations. From a regiochemical perspective, the protocol is complementary to cognate photoredox catalytic olefin aminations, as they typically proceed through either allylic hydrogen atom abstraction or single electron oxidation of the alkene substrate. These methods predominantly result in C-N bond formations at the allylic periphery of the alkene or the less substituted position of the former π-bond (i.e., anti-Markovnikov selectivity). The current process, however, operates through a radical-polar crossover mechanism, which solely affects the selenium catalyst, thus allowing the alkene to be converted strictly through an ionic two-electron transfer regime under Markovnikov control. In addition, it is shown that the corresponding N-vinyl azoles can also be accessed by sequential or one-pot treatment of the allylic azoles with base, thus emphasizing the exquisite utility of this method.

Palladium-Catalyzed Intramolecular Allylic Amidation via Decarboxylative Aromatization: Synthesis of N-Allyl-N-aryl Sulfonamides

A protocol in the preparation of functionalized N-allyl-N-aryl sulfonamides via palladium-catalyzed intramolecular decarboxylative N-allylation reaction is presented. The alkylated 2,5-cyclohexadienyl ketoesters reacted with arylsulfonamides in the presence of titanium tetrachloride and pyridine, which allows the formation of alkylated 2,5-cyclohexadienyl sulfonyl iminoesters which then undergo a palladium-catalyzed intramolecular allylic amidation through decarboxylative aromatization to provide functionalized N-allyl-N-aryl sulfonamides. This allylation protocol proceeds with good regioselectivity. Moreover, we have also shown that N-allyl-N-aryl sulfonamide can be transformed into 4-aryl-1,2,3,4-tetrahydroquinoline and nitrogen-containing β-hydroxysulfide bioactives.

Why Can Cationic Halogen Bond Donors Activate the Ritter-Type Solvolysis of Benzhydryl Bromide but Cationic Hydrogen Bond Donors Can Not?

It is found by experiment that the cationic halogen bond donors (cationic iodoimidazolium compounds) can activate the Ritter-type solvolysis of benzhydryl bromide, while the cationic hydrogen bond donors (cationic imidazolium compounds) could not. To understand the activation mechanism, various noncovalent interactions between benzhydryl bromide and a series of activators in solution, including halogen bond, hydrogen bond, lone pair···π/π+, and C-H···π/π+, were explored theoretically. Our study revealed that the activation difference can be contributed by the variation of the noncovalent interactions. For halogen bond donors, the successful activation is attributed by halogen bond and lone pair···π. The halogen bonds mainly provide the stabilization energy of the ion-pair complex with the help of lone pair···π. For hydrogen-bond donors, the contribution of the hydrogen bond is unable to compensate the like-charge repulsion arising from the generation of the carbocation, leading to the unsuccessful activation. In general, lone pair···π makes a difference.

Synthesis of 2-bromomethyl-2,3-dihydrobenzofurans from 2-allylphenols enabled by organocatalytic activation of N-bromosuccinimide

Activation of NBS in acetic acid and a catalytic amount of DBU promotes an intramolecular oxybromination of 2-allylphenols to produce highly aggregated value and densely functionalized 2-bromomethyl-2,3-dihydrobenzofurans.

Recent progress in selenium-catalyzed organic reactions

Selenium-based catalysts, including organo- and inorganoselenium ones, in organic synthesis in the recent decade are reviewed.

t-BuONa-mediated direct C-H halogenation of electron-deficient (hetero)arenes

An efficient halogenation of electron-deficient (hetero)arenes is described. The reaction utilizes common t-BuONa as a catalyst (for iodination) or a promoter (for bromination and chlorination), and perfluorobutyl iodide, CBr₄ or CCl₄ as the readily-available halogenating agents, respectively. The protocol features broad scope, high efficiency, mild conditions and gram scalability. An ionic pathway involving halogen bond formation and halophilic attack is proposed. The utility of the resulting iodinated heteroarenes is demonstrated in visible light-mediated C_aryl-C_aryl cross-coupling reaction.

Synthesis of Azobenzenes Using N-Chlorosuccinimide and 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU)

A convenient method for the synthesis of symmetrical azobenzenes is reported. This one-step procedure involves treatment of anilines with N-chlorosuccinimide (NCS) and organic base 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). A wide range of commercially available substituted anilines readily participate in this reaction to produce the corresponding azobenzenes in moderate-to-excellent yields in minutes.

Regioselective synthesis of 2,3′-biindoles mediated by an NBS-induced homo-coupling of indoles

An efficient method for the synthesis of 2,3′-biindole and [3,2-a]carbazole derivatives via an NBS-induced homo-coupling of indoles with high regioselectivity.

Visible-light-mediated radical cascade reaction: synthesis of 3-bromocoumarins from alkynoates

The development of a visible-light mediated bromo radical addition/spirocyclization/ester migration cascade reaction to generate 3-bromocoumarins from alkynoates is reported.

Halogen Bonding in Organic Synthesis and Organocatalysis

Halogen bonding is a noncovalent interaction similar to hydrogen bonding, which is based on electrophilic halogen substituents. Hydrogen-bonding-based organocatalysis is a well-established strategy which has found numerous applications in recent years. In light of this, halogen bonding has recently been introduced as a key interaction for the design of activators or organocatalysts that is complementary to hydrogen bonding. This Concept features a discussion on the history and electronic origin of halogen bonding, summarizes all relevant examples of its application in organocatalysis, and provides an overview on the use of cationic or polyfluorinated halogen-bond donors in halide abstraction reactions or in the activation of neutral organic substrates.

Use of Bromine and Bromo-Organic Compounds in Organic Synthesis

Bromination is one of the most important transformations in organic synthesis and can be carried out using bromine and many other bromo compounds. Use of molecular bromine in organic synthesis is well-known. However, due to the hazardous nature of bromine, enormous growth has been witnessed in the past several decades for the development of solid bromine carriers. This review outlines the use of bromine and different bromo-organic compounds in organic synthesis. The applications of bromine, a total of 107 bromo-organic compounds, 11 other brominating agents, and a few natural bromine sources were incorporated. The scope of these reagents for various organic transformations such as bromination, cohalogenation, oxidation, cyclization, ring-opening reactions, substitution, rearrangement, hydrolysis, catalysis, etc. has been described briefly to highlight important aspects of the bromo-organic compounds in organic synthesis.

Hypoiodite-catalysed oxidative cyclisation of Michael adducts of chalcones with 1,3-dicarbonyl compounds: a facile and versatile approach to substituted furans and cyclopropanes

Hypoiodite catalysis for selective oxidative cyclization has been developed, yielding either furans or cyclopropanes with excellent diastereoselectivity.

N-Bromosuccinimide promoted and base switchable one pot synthesis of α-imido and α-amino ketones from styrenes

An N-Bromosuccinimide (NBS) promoted one pot strategy for the synthesis of α-amino functionalized aryl ketones starting from commercially available styrenes has been developed.

One-pot, two-step conversion of alkynes to α-amino (α,α-diamino) ketones with a DMF-activated N-bromoimide strategy

A simple, one-pot, two-step cascade reaction for the synthesis of α-amino ketones has been developed.

Iodine-Catalyzed Decarboxylative Amidation of β,γ-Unsaturated Carboxylic Acids with Chloramine Salts Leading to Allylic Amides

The iodine-catalyzed decarboxylative amidation of β,γ-unsaturated carboxylic acids with chloramine salts is described. This method enables the regioselective synthesis of allylic amides from various types of β,γ-unsaturated carboxylic acids containing substituents at the α- and β-positions. In the reaction, N-iodo-N-chloroamides, generated by the reaction of a chloramine salt with I2 , function as a key active species. The reaction provides an attractive alternative to existing methods for the synthesis of useful secondary allylic amine derivatives.

Metal-free C–N cross-coupling of electrophilic compounds and N-haloimides

When DBU is added, the cross-coupling reaction between alkyl halides (halogen = Cl, Br and I) and N-haloimides (halogen = Cl, Br) occurs, resulting in the formation of aminated products.

N-Bromoacetamide-mediated domino cyclization and elimination of homoallylic trichloroacetimidates: a novel approach toward the synthesis of 1-bromo-2-amino-3-butene derivatives

A practical synthesis of 1-bromo-2-amino-3-butene derivatives from homoallylic trichloroacetimidates was reported. Simply heating the mixture of substrates and N-bromoacetamide in DMF at 90 °C would give the desired products in moderate to excellent yields. The reaction may proceed through a domino bromo-cyclization and elimination pathway. The synthesis of 4,5-dihydrooxazoles from 1-bromo-2-amino-3-butene derivatives was also investigated.

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.

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.