S Sankararaman

Acetals are efficiently and chemoselectively converted into the corresponding aldol ethers upon treatment with 1-trimethylsilyloxycyclohexene 2 in 5 mol dm-3 lithium perchlorate-diethyl ether (LPDE) at ambient temperature with moderate diastereoselectivity, whereas under the same conditions aldehydes and ketals fail to react with 2. The present method allows the acetal substitution to be carried out under neutral reaction and work up conditions. A mechanism involving the formation of an oxocarbenium ion intermediate from the acetal followed by nucleophilic addition of the silyl enol ether is proposed. The observed chemoselectivity is attributed to the mild Lewis acidity of the lithium ion in diethyl ether.

Synthesis of dehydrobenzoannulenes (DBAs) with pyrene core from 1,8-diethynylpyrene and 1,3,6,8-tetraethynylpyrene as building blocks is reported. A sequence involving Sonogashira coupling, Corey- Fuchs reaction and oxidative coupling (Eglinton coupling) is used for the synthesis of pyrene-based dehydrobenzoannulenes. Due to the presence of pyrenechromophore these DBAs and their precursors are highly fluorescent and emit in the visible region, due to extended conjugation of the acetylenic units with the pyrene core. © Indian Academy of Sciences.

1,2,3-Triazolophanes are a class of cyclophanes that has attracted enormous attention in recent times. With the advent of the intramolecular copper-mediated alkyne azide cycloaddition (CuAAC) reaction 1,2,3-triazolophanes of various molecular structure and supramolecular architecture have been synthesized. 1,2,3-Triazolophanes find a variety of applications as molecular hosts, ion sensors, peptidomimics, and supramolecular building blocks, among others. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Photolysis of silyl enol ethers with 2′-nitro- and 2′,2′-dicyanostyrene acceptors yields the corresponding Michael adducts in moderate yield and diastereoselectivity. The desilylation of the silyl enol ethers to the corresponding ketones and cis-trans isomerization of the olefinic acceptors competes with the photochemical Michael addition. Under similar conditions, α,β-unsaturated carbonyl compounds give only cis-trans isomerization. A mechanism involving the regiospecific addition of silyl enol ether to the π-π* excited Michael acceptor to form a zwitterionic intermediate is proposed.

4,5,12,13-Tetraformyl[2.2]paracyclophane (1f) has been prepared for the first time by the cycloaddition of 4,4-diethoxy-2-butynal (3) to 1,2,4,5-hexatetraene (2) under various conditions and hydrolysis of the initially produced bis-acetals 5a and 5b. An X-ray crystal structural analysis of 5a is reported.

Generally, non-aqueous organic redox flow batteries (NAORFBs) operate in glove box conditions to stabilize the charged species generate during energy storage. Even a trace amount of moisture entering the system destabilizes the capacity of the battery. Such systems may not be commercially viable due to stringent ambient requirements. To address this issue, we demonstrate a NAORFB capable of running in inert condition (without glovebox) using a mixed electrolyte of 0.2 M benzylviologen hexafluorophosphate [BV(PF6)2] and N-hexyl phenothiazine (HPT) at 40 mA cm−2 current density. This system exhibits cycling stability up to 100 cycles with 0.0051 % capacity fade per cycle and 6.09 % capacity fade per day.

In the tridentate ligand 2,6-bis(1-benzyl-1H-1,2,3-triazol-4-yl)pyridine, C23H19N7, both sets of triazole N atoms are anti with respect to the pyridine N atom, while in the copper complex aqua-[2,6-bis(1-benzyl-1H-1,2,3-triazol-4-yl)pyridine](pyridine) (tetra-fluoro-borato)copper(II) tetra-fluoro-borate, [Cu(BF4)(C 5H5N)(C23H19N7)(H 2O)]BF4, the triazole N atoms are in the syn-syn conformation. The coordination of the CuII atom is distorted octa-hedral. The ligand structure is stabilized through inter-molecular C - H⋯N inter-actions, while the crystal structure of the Cu complex is stabilized through water- and BF4-mediated hydrogen bonds. Photoluminiscence studies of the ligand and complex show that the ligand is fluorescent due to triazole-pyridine conjugation, but that the fluorescence is quenched on complexation. © 2010 International Union of Crystallography.

Epoxides from α,β-unsaturated ketones undergo highly chemo- and regioselective rearrangement to 1,3-dicarbonyl compounds in 5 mol dm-3 lithium perchlorate-diethyl ether medium by a 1,2-migration of the carbonyl group at ambient conditions. © The Royal Society of Chemistry 1999.

The photophysical properties of two new tetra substituted derivatives of pyrene: 1,3,6,8-tetraethynylpyrene (TEP) and 1,3,6,8-tetrakis(trimethylsilylethynyl)pyrene (TEP-TMS) have been studied. Studies were done with respect to mirror image symmetry in the absorption and emission spectra and permissive or forbidden nature of S0-S1 transition, solvent sensitivity of the first and third vibronic bands and fluorescence anisotropy. Both the derivatives exhibited a strongly allowed S0-S1 transition, high fluorescence quantum yield, shorter fluorescence lifetime compared to pyrene and invariance of the vibronic band intensity ratio to solvent polarity. The behavior of the two pyrene derivatives validates the hypothesis "solvent polarity mediates vibronic coupling and therefore the emission band intensities, for forbidden S0-S1 transitions". The trimethylsilyl derivative (TEP-TMS) was characterized by a strong fluorescence in solid state. The tetraethynyl derivative (TEP) showed high fluorescence anisotropy comparable to the well-known anisotropy probe DPH in glycerol at 0 °C. The fluorescence intensities of TEP and TEP-TMS did not show any significant change in the temperature ranger 0-40 °C for a low viscous solvent like ethanol and in the range 0-60 °C in glycerol. Unlike pyrene, no excimer emission was observed even up to 10-3 M for TEP and TEP-TMS. © 2006 Elsevier B.V. All rights reserved.

Using phenylpropynoic acid (PPA) and 1,4-diazabicyclo[2.2.2]octane (DABCO) as organic spacers, isostructural coordination polymers of Zn(II), Cd(II) and Cu(II) were synthesized by solvothermal method and structurally characterized using single crystal XRD, powder XRD, 13C CP-MAS NMR spectroscopy. Single crystal XRD data revealed four PPA units coordinating with two metal ions forming a paddle wheel secondary building unit (SBU). The paddle wheel units are connected through coordination of DABCO nitrogen to the metal centers from the axial positions leading to the formation of the 1D coordination polymers along the c axis. Intermolecular π stacking and CH⋯π interactions between the adjacent polymer chains convert the 1D coordination polymer into an interesting 3D network with the CH⋯π bonds running along the crystallographic a and b axes. Thermal and nitrogen adsorption studies of these coordination polymers are reported.