Unanticipated switch of reactivity of isonitrile via N≡C bond scission: Cascade formation of symmetrical sulfonyl guanidine.

Unanticipated formation of symmetrical sulfonyl guanidine was observed while treating isonitriles with N,N-dibromoarylsulfonamides in absence of an external amine source. Interesting feature of this work is that one molecule of isonitrile initially reacts with dibromoarylsulfonamide via the C-end to produce the intermediate carbodiimide while the other molecule undergoes C≡N triple bond cleavage to react as amine source with the intermediate. This switch of reactivity from C-center to N-center of the isonitrile generated symmetrical guanidine.

Cascade Synthesis of 5-Aminotetrazoles from Isonitriles and N,N-Dibromoarylsulfonamides via Carbodiimide Coupling with Azide.

A cascade protocol for the synthesis of aminotetrazoles have been developed by treating isonitriles, N,N-dibromoarylsulfonamides, and sodium azides in the presence of K2CO3. This metal-free process proceeds via an isolable carbodiimide intermediate at room temperature, which could further react with sodium azide and subsequently cyclizes intermolecularly to provide 5-aminotetrazoles within a short reaction time. The present protocol's remarkable achievements are the wide substrate scope, good to excellent yields, and good functional group tolerance.

Silver acetate-catalyzed synthesis of cyclic sulfonyl guanidine with exocyclic double bond.

An efficient protocol for the synthesis of cyclic guanidine with exocyclic double bond has been developed. The synthesis has been achieved via intramolecular hydroamination of an intermediate propargyl guanidine by using silver acetate as catalyst in the presence of acetic acid. The reaction proceeds via the formation of acyclic propargyl guanidine in a one-pot reaction of N,N-dibromoarylsulfonamides, isonitriles, and propargylamine in the presence of K2CO3. In the second stage of the synthesis, the acyclic guanidine selectively undergoes 5-exo-dig cyclization in the presence of silver acetate and acetic acid to produce the five-membered cyclic guanidine framework having an exocyclic double bond as the constituent part. Short reaction time, wide substrate scope with good to high yields, and good functional group tolerance are the remarkable achievement of the present protocol.

A Unified Approach for the Synthesis of Isourea and Isothiourea from Isonitrile and N,N-Dibromoarylsulfonamides.

A unified approach has been developed for the synthesis of both isourea and isothiourea in a three-component coupling reaction by treating alcohols or thiols respectively with N,N-dibromoarylsulfonamides and isonitrile and in the presence of K2CO3. This metal-free process proceeds via carbodiimide intermediate at room temperature within a very short reaction time. A library of sulfonylisoureas and isothioureas has been made using this synthetic protocol with wide substrate scope in good to high yields.

Unprecedented 1,3-tert-butyl migration via the C-N single bond scission of isonitrile: an expedient metal-free route to N-sulfonyl amidines.

An unprecedented 1,3-migration of the tert-butyl group was observed while reacting tert-butyl isonitrile with N,N-dibromoaryl sulfonamides and nitrile. The reaction involves the simultaneous C-N single bond scission of isonitrile and the migration of the tert-alkyl group to the adjacent unsaturated nitrogen centre of the nitrile precursor, which eventually results in the formation of N-sulfonyl amidine. This method constitutes a new route for sulfonyl amidine, which does not rely on transition metals. The protocol exhibits a significant advantage in terms of substrate scope and additionally offers an easy synthesis route to guanidine molecules.

A New Schiff Base Based Fluorescent Sensor for Al(III) Based on 2-Hydroxyacetophenone and o-Phenylenediamine.

A simple Schiff base (L) based on 2-hydroxyacetophenone and o-phenylenediamine was prepared which acts as an effective fluorescent sensor for Al3+ with ca. 9.0 fold enhancement in fluorescence intensity and detection limit 10-4.3 M. L can quite clearly distinguish Al3+ over other metal ions Zn2+, Hg2+, Cd2+, Pb2+, Mn2+, Mg2+, Co2+, Ni2+, Cu2+, Ca2+, K+, Li+, Na+ and Fe3+. Cyclic voltammogram and square wave voltammogram of L shows a significant change on interaction with Al3+. Spectroscopic data and DFT calculations confirm 1:1 interaction between L and Al3+ which is reversible with respect to Na2EDTA.

CuI incorporated cobalt ferrite nanoparticles as a magnetically separable catalyst for oxidative amidation reaction.

A Cu-incorporated magnetic nanocatalyst (CoFe2O4@SiO2-SH-CuI) has been developed by immobilizing CuI on the modified surface of CoFe2O4 magnetic nanoparticles. The surface of the silica coated cobalt ferrite magnetic core was first treated with 3-mercaptopropyl triethoxysilane to produce the thiol functionalized nanoparticle CoFe2O4@SiO2-SH. Further treatment of the nanoparticle with CuI produced the desired magnetic nanocatalyst. The versatility of the catalyst has been demonstrated for the synthesis of N-(pyridin-2-yl) benzamide via oxidative amidation of aryl aldehydes with 2-amino pyridine in the presence of an oxidant. The reaction was carried out in DMSO at 80 °C using TBHP (70% aqueous) in the presence of 20 wt% of the catalyst. Notably, the catalyst could be separated from the reaction mixture in the presence of an external magnetic field. During the study, a new compound N-(pyridin-2-yl)anthracene-2-carboxamide has been synthesized and its turn on fluorescence sensing properties towards various metal ions have been studied. Fluorescence experiments and theoretical studies indicated that the newly synthesized carboxamide molecule can be used for fluorescence sensing of the Hg2+ ion in aqueous solution.

Manifestation of Peaks in a Live Firefly Flash.

Several studies have been carried out on flashing of fireflies till now. From patterns of its flashes in different ambient conditions, different conclusions have been drawn and hypotheses put forward. Here we observe flashes emitted by two Indian species of firefly Luciola praeusta and Asymmetricata circumdata. For the species L. praeusta, as the temperature is lowered below about 21 °C, simple pulses become compound or combination ones. Males begin to emit bi-modal flashes while females emit both bi- and tri-modal flashes, along with the simple ones, in a regular manner. For the species A. circumdata, this feature is evident even at their normal flashing temperatures. Though rare, three-peaked flashes do appear from male specimens of both these species, and decay times of all the three peaks in a male- or a female-flash come out to be a few tens of, or a hundred-odd, milliseconds - in contrast to the nanosecond lifetimes determined by different workers for different analogs of the light emitter molecule oxyluciferin. We propose that the tri-modal feature in a flash represents three luminescent forms of the excited state of oxyluciferin, which in the normal flashing state in the living firefly decays via a pathway followed by molecules exhibiting phosphorescence.

Facile, catalyst-free cascade synthesis of sulfonyl guanidines via carbodiimide coupling with amines.

An expeditious catalyst-free cascade coupling of N,N-dibromoarylsulfonamides with isonitriles and amines via carbodiimide intermediates has been developed. The protocol represents an elegant pathway for sulfonyl guanidines at room temperature within a short time with high yields and wide substrate scope. The carbodiimide intermediate could also be isolated in an appreciable yield.

Diastereoselective synthesis of tetrahydropyrans via Prins-Ritter and Prins-arylthiolation cyclization reactions.

An efficient method has been developed for the synthesis of two new classes of tetrahydropyran derivatives comprising amide, tetrazole or benzothiazole moieties via a three-component reaction of 6-methylhept-5-en-2-ol, arylaldehydes and nitriles/thiols in the presence of a tetrafluoroboric acid diethyl ether complex. The reaction proceeds via the formation of an oxocarbenium ion. This protocol is highly diastereoselective and only single diastereomer has been isolated in each case.

A Metal-Free Protocol for Aminofunctionalization of Olefins Using TsNBr2.

N,N-Dibromo-p-toluene sulfonamide (TsNBr2) has been found to be an effective reagent for various aminofunctionalization reactions. This reagent behaves both as an electrophilic bromine source as well as amine to react with olefins under different conditions to yield aminoether, imidazoline, diamine and amino bromine. The reaction proceeds rapidly under mild conditions with high regioselectivity. Olefins react with TsNBr2 in moist THF to form δ-amino ether at room temperature. Treatment of TsNBr2 with olefin in MeCN at room temperature produced imidazoline in high yield. Further modification of the reaction condition resulted in the development of a one-step procedure for the synthesis of N-acetyl,N'-tosyl diamine derivatives directly from olefin. When the olefin was treated with 2.4 mol equiv of TsNBr2 in the presence of K2CO3, N,N'-ditosyl diamine derivative was obtained in moderate yield. Instantaneous formation of aminobromine was observed when an olefin was treated with the reagent in dry CH2Cl2 at room temperature.

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.

A quick Chan-Lam C-N and C-S cross coupling at room temperature in the presence of square pyramidal [Cu(DMAP)4I]I as a catalyst.

A rapid and efficient protocol for C-N and C-S cross coupling has been developed using a new square pyramidal copper complex, [Cu(DMAP)4I]I. The complex was successfully synthesized via a disproportionation reaction of CuI and DMAP in DMSO. The catalytic activity of the complex was found to be excellent for Chan-Lam coupling reaction between aryl boronic acid and amine, amide, azide or thiol. The reaction could be carried out in the presence of only 2 mol% of the copper catalyst in methanol at room temperature within a short time.

Theoretical Insights on the Interaction of N-Heterocyclic Carbenes with Tetravalent Silicon Reagents.

Lewis acid-base type interaction between N-heterocyclic carbene (NHC) and tetravalent silicon reagent (SiR) has been investigated computationally. This NHC-Si interaction is of fundamental importance to the understanding of variety of NHC catalyzed organic transformations involving silicon compounds such as cyanosilylation, trifluoromethylsilylation, etc. Geometries of 24 NHCs, 10 silicon reagents, and their 61 Lewis acid-base complexes have been optimized using the B3LYP/6-31+G(d,p) and M05-2X/6-31+G(d,p) level of theory. The strength of NHC-Si interaction has been assessed in terms of binding energy of the complexes, charge transfer (CT) and the length of Si-CNHC bond. Energy decomposition analysis (EDA) and natural bond orbital (NBO) analysis at M052X/6-31+G(d,p) level of theory has been carried out to get a deeper understanding of the nature of bonding and charge delocalization. Proton affinity of the NHCs and fluoride affinity of the SiRs have been calculated and correlated with the binding energy of the resulting complexes.

Surfactant Dependent pH Controlled "off-on", "off-on-off" and "on-off" Fluorescent Switches Exhibited by N-Benzylidenenaphthalen-1-Amine.

N-benzylidenenaphthalen-1-amine (L) acts as pH dependent "off-on", "off-on-off" and "on-off" fluorescent switch in 1:1 (v/v) CH3CN:H2O depending on the presence of anionic sodiumdocdecyl sulphate (SDS), neutral triton X-100 (TX-100) and cationic cetyltrimethylammonium bromide (CTAB) surfactants respectively. DFT calculation shows the possibility of formation of L.H(+) due to protonation at immine N and L.OH(-) due to introduction of OH(-) group at immine C. The relative stability of these two cationic and anionic species depends on the charge environment provided by surfactants. This influences the photoinduced electron transfer (PET) processes involved and results in different switch behaviour.

A new simple Schiff base fluorescence "on" sensor for Al3+ and its living cell imaging.

The simple Schiff base (Z)-N-benzylidenenaphthalen-1-amine (L) acts as an effective fluorescence sensor for Al(3+) by "off-on" mode, and ca. 42 times enhancement in fluorescence intensity is observed. The detection limit of L towards Al(3+) is observed to be 5 × 10(-5) M. UV/Visible and fluorescence data as well as DFT calculations confirm 1:3 coordination between Al(3+) and L through N atoms in a pyramidal shape. L is employed for imaging the Al(3+) ion in living biological cells and for the determination of the Al(3+) ion in bovine serum albumin.

Formation of Cyclohepta[b]indole Scaffolds via Heck Cyclization: A Strategy for Structural Analogues of Ervatamine Group of Indole Alkaloid.

Ervatamine, silicine, methuenine, etc., are naturally occurring alkaloids that exhibit antimicrobial, anticancer, and anti-HIV activities. Indole fused with a seven-membered carbocyclic ring is a commonly observed structural feature among this series of bioactive compounds. This work describes a strategic approach for the synthesis of cyclohepta[b]indole structural scaffolds. The synthetic strategy consists of a solvent-free Baylis-Hillman reaction of 2-bromobenzaldehydes, followed by iodine-catalyzed C-alkylation of indole with the Baylis-Hillman adducts. Finally, intramolecular Heck coupling reaction using Pd(OAc)2 as catalyst in the presence of benzyltrimethylammonium bromide under microwave condition produced the desired cyclohepta[b]indole derivatives.

Structurally simple ferrocene derivatives for selective cadmium sensing.

Three new ferrocene based Schiff bases 4-{[(E)-ferrocenylmethylidene] amino}benzenethiol (1b), 3-{[(E)-ferrocenylmethylidene]amino} benzenethiol (1c), 2-{[(E)-ferrocenylmethylidene]amino} benzenethiol (1d) have been synthesized to study their sensor property to various metal ions. It has been observed that 1b is highly fluorescent and its fluorescence changes in presence of metal ions. It was further observed that compound 1b is highly selective towards Cd(2+) ion in solution.

A highly efficient catalyst-free protocol for C-H bond activation: sulfamidation of alkyl aromatics and aldehydes.

A catalyst-free protocol has been developed for amidation of alkyl aromatics and aldehydes using TsNBr(2)via a nitrene transfer process in the presence of a base in excellent yield within a short time. The reaction was found to be selective for secondary and tertiary benzylic C-H bonds and C-H bonds of aldehydic groups.