Highly stereoselective synthesis of furano-oxepanes: intramolecular nitrone cycloaddition (INC) reactions on sugar derived 2-substituted allylic ethers

The stereoselective synthesis of furano-oxepanes has been achieved from sugar ethers by an intramolecular nitrone cycloaddition (INC) reaction. The substitution at the 2-position of the allylic group aided in the exclusive formation of oxepanes.     

Broadband supercontinuum generation in a single potassium di-hydrogen phosphate (KDP) crystal achieved in tandem with sum frequency generation

We present here an enhanced broadband supercontinuum generation in a potassium di-hydrogen phosphate (KDP) crystal. The enhancement in the bandwidth of the white light is obtained towards the shorter wavelength regime (<400 nm) by employing supercontinuum generation and sum frequency generation in tandem. The tunability in the blue region of the spectrum with angle is demonstrated. The bandwidth of supercontinuum achieved spans from 350 nm to 1300 nm. Further, we show the excellent polarization maintenance of continuum generated in KDP in comparison to that generated in water and BK-7 glass. PACS 42.65.Ky; 42.65.Jx; 42.65.Re; 42.25.Ja     

An efficient catalytic deprotection of thioacetals employing bismuth triflate: synthesis of pyrrolo[2,1-c] [1,4] benzodiazepines

A simple and efficient deprotection of thioacetals has been achieved by employing bismuth triflate. This method has been effectively employed in the preparation of DNA-binding pyrrolo[2,1-c] [1,4]benzodiazepine and its dimers.     

A facile and efficient ZrCl4 catalyzed conversion of aldehydes to geminal-diacetates and dipivalates and their cleavage

A novel, mild and efficient method has been developed for the preparation of geminal-diacetates and dipivalates in high yields through a reaction of aldehydes with acetic anhydride or pivalic anhydride using Zirconium (IV) chloride as a catalyst under solvent free conditions. Regeneration of aldehydes from the acylals was also achieved using the same catalyst in CH₃OH.     

A one-round,two-prover,zero-knowledge protocol for NP

The model of zero-knowledge multi-prover interactive proofs was introduced by Ben-Or, Goldwasser, Kilian and Wigderson in [4]. A major open problem associated with this model is whether NP problems can be proven by one-round, two-prover, zero-knowledge protocols with exponentially small error probability (e.g. via parallel executions). A positive answer was claimed by Fortnow, Rompel and Sipser in [12], but its proof was later shown to be flawed by Fortnow who demonstrated that the probability of cheating inn independent parallel rounds can be much higher than the probability of cheating inn independent sequential rounds (with exponential ratio between them). In this paper we solve this problem: We show a new one-round two-prover interactive proof for Graph Hamiltonicity, we prove that it is complete, sound and perfect zeroknowledge, and thus every problem in NP has a one-round two-prover interactive proof which is perfectly zero knowledge under no cryptographic assumptions. The main difficulty is in proving the soundness of our parallel protocol namely, proving that the probability of cheating in this one-round protocol is upper bounded by some exponentially low threshold. We prove that this probability is at most 1/2 ^n/9 (wheren is the number of parallel rounds), by translating the soundness problem into some extremal combinatorial problem, and then solving this new problem.     

Crystal structure, superconductivity and magnetic properties of the superconducting ferromagnets Gd1.4−xDyxCe0.6Sr2RuCu2O10 (x=0–0.6)

The structural, electrical and magnetic properties of the superconducting ferromagnets, Gd_1.4−xDy_xCe_0.6Sr₂RuCu₂O₁₀ (x=0–0.6) are systematically investigated as a function of Dy doping and temperature. These compounds are characterized by high temperature superconductivity (T_c ranging from 20 to 40 K depending upon the Dy content) co-existing with weak ferromagnetism with two magnetic transitions (T_M2 ranging from 95 to 106 K and T_M1 around 120 K). Doping with Dy gives no significant structural changes except for a minor change in the c/a ratio. However the superconducting transition temperature is significantly suppressed and magnetic ordering temperature enhanced on Dy doping. These effects are described and discussed.     

Synthesis of chalcone‐based fluorescent polymers: Diels‐Alder reaction of chalcones and their polymerization through ROMP

Ring opening metathesis polymerization (ROMP) was carried out on Diels‐Alder adducts formed from reactions between chalcones and cyclopentadiene. Most of the chalcones gave predominantly endo‐adducts and the exo‐adducts were obtained in good yields from reacting cyclopentadiene with furfurylidine acetone and N,N,diethylaminobenzylidine‐(4‐hydroxy)acetophenone. These exo‐adducts were subjected to ROMP using Grubbs catalyst, bis(tricyclohexylphosphine)benzylidinedichloride. The monomers and polymers were characterized using spectroscopic techniques like FT‐IR, ¹HNMR. The polymers were characterized using TGA, DSC, and GPC. The polymers were found to possess fluorescent properties and poly[2‐(4‐diethylamino)phenyl‐3,5‐divinylcyclopentyl](4‐hydroxyphenyl) methanone was found to have good emissive property at two wavelengths. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1521–1531, 2008     

Electronic transition-moment variation in the B 2ϵ+−X 2Пr system of the AsO molecule

The spectrum of AsO was excited in a quartz discharge tube and the relative band intensities were measured by using photographic photometry. It was found that the electronic transition moment varies as R_e(r) = constant x (1–0.575r) in the range $\text{1.46}\text{A}\text{?}\text{< r < 1.66}\text{A}\text{?}$. Smoothed relative band strengths are derived for the 11 bands.     

Acetoxyborohydride: A Simple Selective Hydroborating Agent

Acetoxyborohydride (CH₃COO$\text{B}$H₃) hydroborates olefins in the presence of some reducible functional groups.