Iodine-mediated electrocatalysis assist Annulation/cyclization via Intramolecular Benzylic C–H Amination: Batch vs Flow Electrochemistry

The access of heterocyclic compounds via direct amination of C-H bonds are of vital interest because of their role in pharmaceutical and natural products. The combination of molecular iodine and electricity activates benzylic C-H bond and facilitates the amination process via intramolecular C-N bond formation. Iodine works as a mediator for the formation of C-N bond via activation of a distance C-H bond through intermediate N-I bond under electrochemical conditions, so iodine can be called electrocatalyst. Under both batch & flow electrochemistry conditions, similar results were obtained in cyclization product with 77 & 78% yields respectively. However, in case of annulation reaction higher yield was obtained with 99% conversion under flow electrochemical conditions using our design of home-made flow microreactor. In both electrochemical transformations, cyclization as well as annulation reaction, no photocatalyst was used. Notably, flow reactions work under safe & environmentally friendly conditions, and continuous products are obtained.

2-Pyridylselenenyl versus 2-Pyridyltellurenyl Halides: Symmetrical Chalcogen Bonding in the Solid State and Reactivity towards Nitriles

The synthesis of 2-pyridyltellurenyl bromide via Br2 oxidative cleavage of the Te–Te bond of dipyridylditelluride is reported. Single-crystal X-ray diffraction analysis of 2-pyridyltellurenyl bromide demonstrated that the Te atom of 2-pyridyltellurenyl bromide was involved in four different noncovalent contacts: Te⋯Te interactions, two Te⋯Br ChB, and one Te⋯N ChB contact forming 3D supramolecular symmetrical framework. In contrast to 2-pyridylselenenyl halides, the Te congener does not react with nitriles furnishing cyclization products. 2-Pyridylselenenyl chloride was demonstrated to easily form the corresponding adduct with benzonitrile. The cyclization product was studied by the single-crystal X-ray diffraction analysis, which revealed that in contrast to earlier studied cationic 1,2,4-selenadiazoles, here we observed that the adduct with benzonitrile formed supramolecular dimers via Se⋯Se interactions in the solid state, which were never observed before for 1,2,4-selenadiazoles.

Synthesis of 4-Substituted-1,2-Dihydroquinolines by Means of Gold-Catalyzed Intramolecular Hydroarylation Reaction of N-Ethoxycarbonyl-N-Propargylanilines

An alternative Au(I)-catalyzed synthetic route to functionalized 1,2-dihydroquinolines is reported. This novel approach is based on the use of N-ethoxycarbonyl protected-N-propargylanilines as building blocks that rapidly undergo the IMHA reaction affording the 6-endo cyclization product in good to high yields. In the presence of N-ethoxycarbonyl-N-propargyl-meta-substituted anilines, the regiodivergent cyclization at the ortho-/para-position is achieved by the means of catalyst fine tuning.

Superelectrophilic carbocations: preparation and reactions of a substrate with six ionizable groups

A substrate has been prepared having two triarylmethanol centers and four pyridine-type substituent groups. Upon ionization in the Brønsted superacid CF3SO3H, the substrate undergoes two types of reactions. In the presence of only the superacid, the highly ionized intermediate(s) provide a double cyclization product having two pyrido[1,2-a]indole rings. With added benzene, an arylation product is obtained. A mechanism is proposed involving tetra-, penta-, or hexacationic species.

Synthesis of Imidazolium Based Ionic Liquids and its Application as Medium in Cyclization Reaction of Diketone

Ionic liquids (ILs) are organic salts that have a liquid phase under 100°C. Due to its ionic nature, it has affinity with water as well as organic compounds that make it potential to be developed as solvents with tuneable property. One class of material that possess this property is imidazolium compound which serves as organic cation. Variations of substituents (alkyl or aryl groups) in the parent cation provide several compounds that can be used as medium in various reactions. In this research, the synthesis of several imidazolium based ionic liquids had been performed utilizing Microwave Assisted Organic Synthesis (MAOS) method namely: butyl-methyl imidazolium chloride (BMIM-Cl), Decyl-methyl imidazolium bromide (DMIM-Br), Dodecyl-methyl imidazolium bromide (DDMIM-Br). The ILs were subsequently used as medium in cyclization reactions of diketone to provide an alternative route to flavanon. The structure of the synthesized ILs and the cyclization product were characterized by FT-IR and 1H-NMR spectroscopy. The yield of the synthesized ILs were moderate (24-87%) while the yield of cyclization reactions was high (99%). The formation of the cyclization product, was clearly indicated by the 1H-NMR spectrum with the peaks that appear at 6.81 ppm as singlet which corresponded to the proton at the pyranone ring.

An Unexpected Dihalogenation/Dehydrogenation Product Derived­ via Iodolactonization of an N-Tosyl-N-[6-(2-cyclopenten-1-yl)-2-methylphenyl]glycine

The reaction between N-tosyl-N-[6-(2-cyclopenten-1-yl)phenyl]glycine (syn/anti atropisomeric mixture) and molecular iodine is studied. Along with the expected 8-exo-cyclization product possessing a 3-iodo-2,3,3a,6,7,11b-hexahydrobenzo[e]cyclopenta[g][1,4]oxazocine core, the unexpected 1,11b-dehydrogenated/1-iodinated analogue with a 1,3-diiodo-3,3a,6,7-tetrahydrobenzo[e]cyclopenta[g][1,4]oxazocine structure is observed for the first time in a conventional halolactonization reaction.

Copper-Catalyzed Synthesis of Fused Imidazopyrazine N-Oxide Skeletons

N-Propargyl-2-aroylimidazoles synthesized and converted into the corresponding ketoximes. Under various conditions, several mono- and diketoxime imidazole derivatives were formed by converting the carbonyl or carbonyl and propargyl groups into oxime groups. N-Propargyl monooxime imidazole derivatives were cyclized by treatment with CuI to give various imidazopyrazine N-­oxides. Several copper salts, such as CuOAc, CuSO4, and CuOTf, formed the same cyclization product. This cyclization reaction occurred only in the presence of Cu(I) or Cu(II) salts; other transition metals such as Au, Ag, In, and Fe did not yield cyclic products. The nucleus-independent chemical shift method was used to calculate the aromaticity of the bicyclic rings.

Nucleophilic and electrophilic cyclization of N-alkyne-substituted pyrrole derivatives: Synthesis of pyrrolopyrazinone, pyrrolotriazinone, and pyrrolooxazinone moieties

Intramolecular nucleophilic and electrophilic cyclization of N-alkyne-substituted pyrrole esters is described. Efficient routes towards the synthesis of pyrrolopyrazinone, pyrrolotriazinone and pyrrolooxazinone have been developed. First, N-alkyne-substituted pyrrole ester derivatives were synthesized. Introduction of various substituents into the alkyne functionality was accomplished by a copper-catalyzed cross-coupling reaction. Nucleophilic cyclization of N-alkyne-substituted methyl 1H-pyrrole-2-carboxylates with hydrazine afforded the 6-exo-dig/6-endo-dig cyclization products depending on the electronic nature of the substituents attached to the alkyne. On the other hand, cyclization of N-alkyne-substituted methyl 1H-pyrrole-2-carboxylates with iodine only resulted in the formation of the 6-endo-dig cyclization product regardless of the substitution of the alkyne functionality.

Fluorescence light-up detection of cyanide in water based on cyclization reaction followed by ESIPT and AIEE

Sensor 1 could undergo an oxidative cyclization reaction and then generate hydroxyphenylbenzoxazole 2 when CN− was present as a catalyst. The cyclization product 2 displayed fluorescence properties in the micellar due to the AIEE as well as ESIPT effect. This reaction process could be used for the light-up detection of CN− in water.