Insights into the Oxidation Chemistry of 2‐Hydroxypurine by Electrochemical Methods

The oxidation chemistry of 2‐hydroxypurine has been investigated in phosphate containing supporting electrolytes at pH 1.4–9.8 at a pyrolytic graphite electrode by voltammetric studies, spectral studies, controlled potential electrolysis and related techniques. The kinetics of decay of the UV‐absorbing intermediate generated during electrooxidation was followed spectrophotometrically and the decay occurred in a pseudo‐first‐order reaction. The course of the electrode reaction has been deduced to involve a 6e, 6H⁺ oxidation of 2‐hydroxypurine via the formation of 2, 8‐dihydroxypurine. The electrooxidation of 2‐hydroxypurine has been found to be an EC reaction (electrode reaction followed by chemical reactions) in which charge transfer is followed by competitive chemical reactions. A detailed interpretation of the redox mechanism of 2‐hydroxypurine has been presented.     

Visible Light‐Induced,Metal‐Free Denitrative [3+2] Cycloaddition for Trisubstituted Pyrrole Synthesis

A metal‐free, regioselective synthesis of trisubstituted pyrroles has been developed through a formal [3+2] cycloaddition reaction between 2H‐azirines and nitroalkenes under visible light/photoredox‐catalyzed conditions. The reaction proceeds through 2H‐azaallenyl radical addition on β‐nitrostyrenes in a Michael fashion followed by a base‐mediated denitration reaction. The directive group influence of the nitro group controls the regiochemistry of the reaction.     

An Environment‐friendly Synthesis of 2,3‐Disubstituted‐2‐iminothiazoline‐4‐ones

A series of 2,3‐substituted‐2‐iminothiazoline‐4‐ones derivatives have been synthesized via an improved method including an auto‐catalyzed reaction. This method avoided using any extra catalyst except for the reaction material. This method has been successful in both the aromatic substituted 2‐iminothiazolines and the alkyl substituted 2‐iminothiazolines. The special product with a hydroxyl group on the 2‐iminogroup of 1,3‐thiazoline‐4‐ones has also been obtained unexpectedly. The possible mechanism has been proposed for the special process of dealkylation and hydroxylation. This method offered a special way to afford the 2‐hydroxyimino‐substituted thiazoline‐4‐one derivatives in an efficient and eco‐friendly way. The mechanism of the transformation under acid condition has also been proposed.     

Ab initio Study of Mechanism of Cycloaddition Reaction between Germylene Silylene (H2GeSi:) and Acetone

The mechanism of the cycloaddition reaction between singlet germylene silylene (H₂GeSi:) and acetone has been investigated with CCSD(T)/6‐31G*//MP2/6‐31G* method. From the potential energy profile, we could predict that the reaction has two competitive dominant reaction channels. The present rule of this reaction is that the [2+2] cycloaddition reaction of the two (‐bonds in germylene silylene and acetone generates a four‐membered ring silylene with Ge. Because of the unsaturated property of Si atom in the four‐membered ring silylene with Ge, it could further react with acetone, resulting in the generation of a bis‐heterocyclic compound with Si and Ge. Simultaneously, the ring strain of the four‐membered ring silylene with Ge makes it isomerize to a twisted four‐membered ring product.     

Regioselective Synthesis of 3‐(Imidazol‐4‐yl) Indolin‐2‐Ones under Microwave Heating

A formal [3 + 2] cyclization reaction of 3‐(2‐oxo‐2‐arylethylidene)indolin‐2‐ones and amidines has been developed, regioselectively affording a series of new 3‐(imidazol‐4‐yl)indolin‐2‐ones in good to excellent yields. The reaction was easily conducted in ethylene glycol using Cs₂CO₃ as a base promoter under microwave irradiation. Flexible structural modification, and broad functional group compatibility as well as mild reaction conditions make this strategy a useful and attractive process of library generation for drug discovery.     

Solvent polarity and hydrogen bond effects on nucleophilic substitution reaction of 2‐bromo‐5‐nitrothiophene with piperidine

The reaction kinetics of 2‐bromo‐5‐nitro thiophene with piperidine was studied in a solvent with a mixture of propan‐2‐ol with methanol and n‐hexane at 25°C. The measured rate coefficients of the reaction demonstrated dramatic variations in propan‐2‐ol–n‐hexane mixtures and mild variations in propan‐2‐ol–methanol system. The second‐order rate coefficients of the reaction, k_A, decreased sharply with n‐hexane content. The multiparameter correlation of log k_A versus molecular‐microscopic solvent parameters shows interesting results in these solutions. Linear free energy relationship investigations confirm that polarity has a major effect on the reaction rate and hydrogen bond ability of the media has a slight effect on the reaction rate. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 185–190, 2011     

Theoretical studies on the mechanism of formation of a heteropolycyclic germanic compound between dimethyl‐germylidene and ethylene

Mechanism of the cycloadditional reaction between singlet dimethyl‐germylidene (R1) and ethylene (R2) has been investigated with MP2/6‐31G* method, including geometry optimization and vibrational analysis for the involved stationary points on the potential energy surface. The energies of the different conformations are calculated by CCSD(T)//MP2/6‐31G* method. From the potential energy profile, it can be predicted that the dominant reaction pathway of the cycloadditional reaction of forming a heteropolycyclic germanic compound between singlet dimethyl‐germylidene and ethylene consists of three steps: (1) the two reactants (R1, R2) first form a three‐membered intermediate (INT1) through a barrier‐free exothermic reaction of 39.6 kJ/mol. (2) Three‐membered intermediate (INT1) isomerizes to an active four‐membered intermediate (INT2) via a transition state (TS2), for which the barrier is 50.1 kJ/mol. (3) Four‐membered intermediate (INT2) reacts further with ethylene (R2) to form a heteropolycyclic germanic compound (P3), which is also a barrier‐free exothermic reaction of 87.7 kJ/mol. This dominant reaction has an excellent selectivity and differs considerably from its competitive reactions in thermodynamic property and reaction rate. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

A Simple One-pot Synthesis of Indeno[2,1-f]quinolin-3-one Derivatives under Microwave Irradiation

A series of new indeno[2,1‐f]quinolin‐3(2H)‐one derivatives were synthesized by a reaction of aromatic aldehyde with Meldrum's acid (2,2‐dimethyl‐1,3‐dioxane‐4,6‐dione) and 9H‐fluoren‐2‐amine under microwave irradiation without catalyst in glacial acetic acid. This reaction has notable advantages of short reaction time, high yield and convenient operation.     

Copper‐Assisted/Copper‐Free Synthesis of Functionalized Dibenzo[b,f]oxepins and Their Analogs via a One‐Pot Tandem Reaction

A simple, convenient, and efficient method for the formation of functionalized dibenzo[b,f]oxepins and their analogs bearing both electron‐donating and electron‐withdrawing groups has been developed via a one‐pot cascade reaction. Most starting materials are commercially available 2‐(2‐hydroxyphenyl)acetonitriles and 2‐haloarylaldehydes. The procedure makes use of Cs₂CO₃ as the base, and DMF as solvent under copper‐assisted/copper‐free conditions. The reaction has a comprehensive group tolerance for substrates. Most of the reactions were complete within 1 h in good‐to‐excellent yields, and the reaction temperatures were relatively low. The protocol could be scaled up to grams without lowering the yield. A reaction mechanism was also proposed.     

Ab initio study of the mechanism of forming a spiro‐heterocyclic ring compound involving Si and Ge from dichlorosilylene germylidene(Cl2SiGe:) and formaldehyde

The mechanism of the cycloaddition reaction between singlet dichlorosilylene germylidene (Cl₂Si?Ge:) and formaldehyde has been investigated with the CCSD(T)//MP2/6‐31G* method. From the potential energy profile, it could be predicted that the reaction has one dominant reaction pathway. The reaction rule presented is that the two reactants first form a four‐membered Si‐heterocyclic ring germylene through the [2 + 2] cycloaddition reaction. Because of the 4p unoccupied orbital of Ge atom in the four‐membered Si‐heterocyclic ring germylene and the π orbital of formaldehyde forming a π→p donor–acceptor bond, the four‐membered Si‐heterocyclic ring germylene further combines with formaldehyde to form an intermediate. Because the Ge atom in intermediate undergoes sp3 hybridization after transition state, then, the intermediate isomerizes to a spiro‐heterocyclic ring compound involving Si and Ge via a transition state. © 2012 Wiley Periodicals, Inc.     

ECEC and ECE‐Type Mechanisms in Electrochemical Oxidation of 4‐Substituted Catechols in the Presence of 4‐Hydroxy‐6‐methyl‐2‐pyrone

Electrochemical oxidation of 3,4‐dihydroxybenzoic acid ( 1 ) and 4‐tert‐butylcatechol ( 5 ) in the presence of 4‐hydroxy‐6‐methyl‐2‐pyrone ( 2 ) as nucleophile in aqueous solution has been studied using cyclic voltammetry and controlled‐potential coulometry. The results indicate that 1 via Michael reaction under electro‐decarboxylation reaction converts to heterocyclic compound 4 , and the quinone derived from 4‐tert‐butylcatechol ( 5 ) participates in Michael reaction with 2 and through an ECE mechanism converts to the corresponding o‐quinone ( 6a ). The electrochemical synthesis of 4 and 6a has been successfully performed in an undivided cell.     

DABCO‐Catalyzed Efficient Synthesis of Naphthopyran Derivatives via One‐Pot Three‐Component Condensation Reaction at Room Temperature

Diazabicyclo[2.2.2]octane (DABCO) has been used as a mild and efficient catalyst for synthesis of 2‐amino‐3‐cyano naphthopyran derivatives via a one‐pot three‐component reaction of aromatic aldehydes, naphthols, and malononitrile at room temperature. The short reaction times, easy workup, good to excellent yields, and mild reaction conditions make this domino Knoevenagel–Michael reaction both practical and attractive.     

New results on the reactivity of 5,6‐diamino‐4‐hydroxy‐2‐mercaptopyrimidine

The reaction of 5,6‐diamino‐4‐hydroxy‐2‐mercaptopyrimidine with mono‐ and α,ω‐dihalocompounds has been reinvestigated. Alkyl derivatives of 5‐amino group, not previously described, have been obtained as reaction products. A comparison with the reactivity of 6‐amino‐4‐hydroxy‐2‐mercaptopyrimidine has been also performed.     

A Facile and Efficient Solid Supported,One‐Pot Synthesis of Functionalized Piperidine Derivatives Catalyzed by Amberlite IRA400‐Cl Resin/I2/KI via Multicomponent Reaction

A facile and efficient one‐pot, solid supported synthesis of functionalized piperidine derivatives catalyzed by Amberlite IRA400‐Cl resin/I₂/KI via a multicomponent reaction of various aldehydes, aromatic amines, and 1,3‐dicarbonyl compounds has been achieved. The reaction has been carried out in a one‐pot reaction and Amberlite resin as a solid supported catalyst at room temperature. Shorter reaction time, easy workup, yield, and mild reaction condition make the novel synthetic strategy both practical and attractive.     

Synthesis of networked polymer based on ring‐opening addition reaction of 1,3‐benzoxazine with resorcinol

A highly efficient ring‐opening addition reaction of benzoxazine at ambient temperature has been developed with 2‐methylresorcinol as a nucleophilic reagent. In this reaction, 2‐methylresorcinol reacted with two equivalent amount of benzoxazine to give the corresponding 1:2 adduct, demonstrating its potential as a bifunctional nucleophile. Based on this reaction, a new crosslinking system consisting of a polymer bearing benzoxazine moieties in the side chains and 2‐methylresorcinol as a crosslinker has been performed to obtain the corresponding networked polymer. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Potassium carbonate,a support for the green synthesis of azoles and diazines

A novel potassium carbonate mediated synthesis of 2‐amino‐1,3‐thia/oxa zoles, 2‐amino‐1,3,4‐thia/oxa diazines and 2‐hydrazino‐1,3,4‐thiadiazines has been described here. The use of K₂CO₃ allows for an aqueous workup thereby eliminating the organic solvent from both the reaction step and post reaction stage, without compromising the yield and reaction time.     

An Enolate‐Mediated Organocatalytic Azide–Ketone [3+2]‐Cycloaddition Reaction: Regioselective High‐Yielding Synthesis of Fully Decorated 1,2,3‐Triazoles

An enolate‐mediated organocatalytic azide–ketone [3+2]‐cycloaddition (OrgAKC) reaction of a variety of enolizable arylacetones and deoxybenzoins with aryl azides was developed for the synthesis of fully decorated 1,4‐diaryl‐5‐methyl(alkyl)‐1,2,3‐triazoles in excellent yields with high regioselectivity at 25 °C for 0.5–6 h. This reaction has an excellent outcome with reference to reaction rate, yield, regioselectivity, operation simplicity, and availability of substrates and catalyst. This reaction has advantages over the previously known metal‐mediated reactions.     

Phosphorylated Aminoacetal in the Synthesis of New Acyclic,Cyclic, and Heterocyclic Polyphenol Structures

New phosphorylated aminoacetal has been synthesized by the Kabachnik–Fields reaction; its reactivity has been studied in acid‐catalyzed condensation with linear polyphenols (2‐methylresorcinol, resorcinol, pyrogallol) and the Mannich reaction with macrocyclic polyphenol (calix[4]resorcinol). It has been determined for the first time that acid‐catalyzed reaction of phosphorus‐containing acetal with resorcinol and its derivatives in ethanol in the presence of hydrochloric acid gives new phosphorylated piperazines in addition to the compounds of diarylmethane series. Condensation of macrocyclic polyphenol (calix[4]resorcinol) with formaldehyde and N‐((dihexylphosphoryl)methyl)‐2, 2‐dimethoxyethylamine (the Mannich reaction) has resulted in novel tetrasubstituted calixarene containing aminophosphine oxide and acetal groups on the “upper rim” of molecule.     

Theoretical study of mechanism of cycloaddition reaction between dimethyl‐silylene carbene [(CH3)2SiC:] and formaldehyde

The mechanism of the cycloaddition reaction between singlet dimethyl‐silylene carbene and formaldehyde has been investigated with MP2/6‐31G* method, including geometry optimization and vibrational analysis for the involved stationary points on the potential energy surface. The energies of the different conformations are calculated by zero‐point energy and CCSD (T)//MP2/6‐31G* method. From the potential energy profile, it can be predicted that the reaction has two competitive dominant reaction pathways. The main products of first dominant reaction pathway are a planar four‐membered ring product (P4) and its H‐transfer product (P4.2). The main product of second dominant reaction pathway is a silicic bis‐heterocyclic compound (P5). © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Cu（I）-Catalyzed Synthesis of 2-Substituted Benzimidazoles from 2-lodoanilines and Amides

A novel and efficient approach to the synthesis of 2-substituted benzimidazoles has been developed via CuI/DMEDA-catalyzed coupling reaction and post-cyclization with glacial acetic acid from readily available 2-iodoanilines and amides. This method is suitable for the construction of a variety of benzimidazoles in moderate to good yields under short reaction times.