The skeletal rearrangement of gold- and platinum-catalyzed cycloisomerization of cis-4,6-dien-1-yn-3-ols: pinacol rearrangement and formation of bicyclo[4.1.0]heptenone and reorganized styrene derivatives

With gold and platinum catalysts, cis-4,6-dien-1-yn-3-ols undergo cycloisomerizations that enable structural reorganization of cyclized products chemoselectively. The AuCl3-catalyzed cyclizations of 6-substituted cis-4,6-dien-1-yn-3-ols proceeded via a 6-exo-dig pathway to give allyl cations, which subsequently undergo a pinacol rearrangement to produce reorganized cyclopentenyl aldehyde products. Using chiral alcohol substrates, such cyclizations proceed with reasonable chirality transfer. In the PtCl2-catalyzed cyclization of 7,7-disubstituted cis-4,6-dien-1-yn-3-ols, we obtained exclusively either bicyclo[4.1.0]heptenones or reorganized styrene products with varied substrate structures. On the basis of the chemoselectivity/structure relationship, we propose that bicyclo[4.1.0]heptenone products result from 6-endo-dig cyclization, whereas reorganized styrene products are derived from the 5-exo-dig pathway. This proposed mechanism is supported by theoretic calculations.     

A concise synthesis of quinazolinone TGF-β RI inhibitor through one-pot three-component Suzuki-Miyaura/etherification and imidate-amide rearrangement reactions

A simple and efficient synthesis of dihydropyrrolopyrazole boronic acid intermediate (5) has been developed. Utilization of a three-component Suzuki-Miyaura/etherification with microwave heating led to advanced compound 11 in high yield and with easy purification. Reaction of compound 11 with methanesulfonyl chloride at room temperature furnished the 1,3 O-N rearranged product (12), which is postulated to proceed via an intramolecular mechanism. The outlined synthesis provides a highly efficient and high-yielding route that is amenable to rapid analog synthesis.     

Molecular clips form isostructural dimeric aggregates from benzene to water

We report the synthesis and characterization of eight C-shaped methylene-bridged glycoluril dimers (1-8) bearing hydrogen-bonding amide groups on their aromatic rings. Compounds 1-6 undergo tight dimerization in CDCl3 solution (Ks > 9 x 10(5) M(-1)); binary mixtures of 1-7 form mixtures of homodimers and heterodimers in moderately selective dimerization processes (0.23 < or = Keq < or = 768; 0.253 < or = chiAB < 0.933). The high affinity formation of 1.1-6.6 is due to the commensurate nature of the geometrical constraints imposed by the pi-pi interactions and only two hydrogen bonds. The differential response of the strengths of the pi-pi interactions and H-bonds of 2.2 to changes in solvent polarity--from C6D6 to D2O--results in the formation of a solvent-independent isostructural aggregate that exhibits high affinity dimerization across the full range of solvents.     

Ternary iron(II) complex with an emissive imidazopyridine arm from Schiff base cyclizations and its oxidative DNA cleavage activity

The ternary iron(II) complex [Fe(L')(L")](PF6)3(1) as a synthetic model for the bleomycins, where L' and L" are formed from metal-mediated cyclizations of N,N'-(2-hydroxypropane-1,3-diyl)bis(pyridine-2-aldimine)(L), is synthesized and structurally characterized by X-ray crystallography. In the six-coordinate iron(ii) complex, ligands L' and L" show tetradentate and bidentate chelating modes of bonding. Ligand L' is formed from an intramolecular attack of the alcoholic OH group of L to one imine moiety leading to the formation of a stereochemically constrained five-membered ring. Ligand L" which is formed from an intermolecular reaction involving one imine moiety of L and pyridine-2-carbaldehyde has an emissive cationic imidazopyridine pendant arm. The complex binds to double-stranded DNA in the minor groove giving a Kapp value of 4.1 x 10(5) M(-1) and displays oxidative cleavage of supercoiled DNA in the presence of H2O2 following a hydroxyl radical pathway. The complex also shows photo-induced DNA cleavage activity on UV light exposure involving formation of singlet oxygen as the reactive species.     

Thermal properties of bisitaconimide and bisbenzoxazine blends

Blends of cardanol-based bisbenzoxazine (BZc) and 4,4′-bisitaconimidodiphenyl ether (BIM) having nine different mass ratios (i.e. 100:0, 90:10, 75:25, 60:40, 50:50, 40:60, 25:75, 10:90 and 0:100) were prepared and their curing behaviour was studied by differential scanning calorimetry (DSC) and fourier transform infrared spectroscopy. A curing mechanism comprising two-steps: (1) homopolymerization and co-curing reaction of itaconimide with alkyl side chain double bonds of cardanol BZc at lower temperature (~443 K) and (2) ring-opening polymerization of oxazine at higher temperature (~453–483 K) has been proposed. The T _g of the cured resin blends was determined by DSC and the increase in BIM content in the blend resulted in an increase in T _g from 408 K BZc to 474 K BIM. Increase in bisitaconimide content resulted in improvement of char yield at 1,073 K as well as an increase in mass loss temperatures (5 and 10 %). Compared to BZc, the blends showed a higher thermal stability. The lap shear strength of these blends in metal–metal joints was investigated at 323, 523 and 573 K.     

Stepwise Self-assembly of a Tripeptide from Molecular Dimers to Supramolecular β-sheets in Crystals and Amyloid-like Fibrils in the Solid State

The terminally protected tripeptide Boc–Ala(1)–Leu(2)–Ala(3)–OMe 1 forms antiparallel hydrogen-bonded dimers of two different conformers in the asymmetric unit and the individual dimers then self-associate to form supramolecular β-sheet structures in crystals and amyloid-like fibrils in the solid state.     

Modification of Poly(2, 6-dimethyl-1,4-phenylene Oxide): Phosphorylation Studies

Side chain bromination of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) was carried out by using N-bromosuccinimide followed by phosphorylation of the bromo derivative with triethyl phosphite. Optimum conditions for minimum gel formation have been established. The products have been characterized by 'H-NMR and IR studies. Thermal behavior was investigated by thermogravimetry and differential scanning calorimetry in an air nitrogen atmosphere. Phosphorylated PPO starts to lose weight at 200°C, but the char yield increases with an increase in the phosphorus content of the polymer.     

Blends of benzoxazine monomers

This article describes synthesis, characterization and properties of blends of benzoxazine (Bz) monomers, i.e., m-alkylphenyl-3,4-dihydro-2H-benzoxazine (Bz-C), 6,6′-(propane-2,2-diyl)bis(3-phenyl-3,4-dihydro-2H-benzoxazine (Bz-A) and 3-phenyl-3,4-dihydro-2H-benzoxazine-p-carboxylic acid (Bz-pA). Binary blends of Bz-C with Bz-pA, and Bz-A with Bz-pA were prepared by first synthesizing Bz-C or Bz-A followed by the addition of all the ingredients of Bz-pA. In a similar manner, ternary blends of Bz-C, Bz-A and Bz-pA were prepared by first synthesizing Bz-C and subsequent addition of all the ingredients of Bz-A and Bz-pA in one pot. The Bz monomer blends were characterized by ¹H-NMR, FTIR spectroscopy, and differential scanning calorimetry. The temperature of onset of curing (T _o), due to ring-opening polymerization of Bz was found to decrease significantly by incorporation of carboxyl groups (Bz-pA) showing thereby the catalytic effect of acid functionality. Bz polymers showed good thermal stability and incorporation of Bz-pA in blends resulted in a highly cross-linked network. The interlaminar shear strength of glass fabric reinforced composites and the lap shear strength of metal–metal joints using these resin blends was also investigated.     

Novel betaines/mesoionic compounds via a simple and convenient MCR in aqueous micellar system: synthesis of thiazolo[2,3-a]isoquinolin-4-ium derivatives

An inexpensive one-pot green methodology has been developed for the synthesis of thiazolo[2,3-a]isoquinolin-4-ium derivatives by the reaction of different derivatives of isoquinoline and 2-bromoacetophenone/bromoacetonitrile with benzoyl isothiocyanate in aqueous micellar medium.