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Abstract: 4-R-Substituted 2-nitro-1-nitrosoethylbenzenes (R = H, [CH.sub.3], O[CH.sub.3], Cl, F) have been synthesized under solvent-free conditions and the mechanism of their tautomerization to 2-isonitroso-1-nitro-2-phenylethanes have been investigated by ¹H NMR [...]

The dynamic [super 1]H NMR studies of the primary carbamates in the solvants CD[Cl.sub.3] and C[D.sub.3]COC[D.sub.3] is presented. The free energies of activation are attributed to the conformational isomerization about the N-C bond and these barriers to rotation have indicated solvent dependence in contrast to the tertiary analogues and are lower in free energy by ca. 2-3 kcal [mol.sup.-1].

Small peptides are valuable peptides due to their extended biological activities. Their activities could be categorized according to their low antigenicity, osmotic pressure, and also because of their astonishing bioactivities. For example, the aggression of Phe-Phe fibers via self-assembly and intermolecular hydrogen bonding is the main reason for the formation of Alzheimer’s β-amyloid fibrils. Hydrogen bonding is the main intramolecular interaction in peptides, while the presence of aromatic ring leads to the π-π stacking and affects the self-assembly and aggression. Thus, insertion of an unusual amino acid into peptide sequence facilitates the formation of intramolecular bonds, lipophilicity and its conformation. To design new small peptides with remarkable lipophilicity, it is an idea to employ γ-amino acid, such as gabapentin (H2N-Gpn- OMe) and baclofen (H2N-Baclofen-OMe), in the structure of small peptides to increase cellpenetrating properties and to prevent aggression of Phe-Phe fibrils in β-amyloids of Alzheimer’s disease. Some new tri- and tetrapeptides were synthesized through introducing biologically active gabapentin and baclofen to dipeptide of phenylalanine (Phe-Phe) through solution phase peptide synthesis strategy. [ABSTRACT FROM AUTHOR]

An efficient palladium-catalyzed protocol was developed for the synthesis of 3-arylidene-2-oxindoles. The synthesis involved a sequential one-pot six-component reaction via Ugi/Heck carbocyclization/Sonogashira/nucleophilic addition to yield desired skeleton.

The effect of the exocyclic conjugation, via d-p orbital interaction and/or negative hyperconjunction of the N-S bond, on the inversion of the morpholine ring in some N-arylsulfonyl morpholines is analyzed by using variable-temperature [super 1]H NMR spectroscopy in different solvents. The studies have shown that sulfonamide group has preferred a conformation with the S-C bond antiperiplanar with respect to the nitrogen atom lone pair and the uC[H.sub.2]-N-C[H.sub.2]-moieties in staggered with the S-O bonds of the S[O.sub.2] group.

A transition-metal-free postmodification of the Groebke-Blackburn-Bienaymé (GBB) reaction for the synthesis of spiro[chromene-imidazo[1,2- a ]pyridin]-3'-imine was discovered. The unusual transformation represents the first example of activation and the reaction of the imidazole carbon atom. In this postcondensational modification, KO t -Bu acts as a base, which, after the isomerization of an alkyne moiety to allene, causes the next unique nucleophilic reaction of the imidazole carbon atom that results in spirocyclic structures. The proposed reaction mechanism was confirmed based on the DFT calculations.

Practical Pd-catalyzed 2-pyridones were designed to achieve chromeno[2,3- b ]pyridine-2-ones. The reaction proceeds through domino nucleophilic addition and decarboxylative arylation, respectively. This methodology offers a moderately efficient approach to construct the bioactive, fused-heterocyclic skeletons via selective C-O bond formation and decarboxylative arylation in a single step with high selectivity and good yields.

The effect of the exocyclic conjugation, via d-p orbital interaction and/or negative hyperconjugation (anomeric effect) of the N-S bond, on the inversion of the morpholine ring in some N-arylsulfonyl morpholines is studied by variable-temperature (1)H NMR spectroscopy in different solvents. The observed free energy barriers are 9.2-10.3 kcal mol(-1); the lower values were obtained with increasing conjugation (substituents of higher electron withdrawing power) along the series. The barrier to ring inversion of 1e was solvent independent. X-ray data of compounds 1b,d reveal the chair conformation of the six-membered ring, the flattened pyramidal orientation of the ring nitrogen atom, and the sulfonyl group in equatorial position with the plane containing the C(aryl)-S-N bond perpendicular to the plane of the benzene ring. In addition, the sulfonamide group prefers a conformation with the S-C bond antiperiplanar with respect to the nitrogen atom lone pair and the -CH(2)-N-CH(2)- moieties in staggered conformation with the S-O bonds of the SO(2) group.

The dynamic 1H NMR study of some primary carbamates in the solvents CDCl3 and CD3COCD3 between 183 and 298 K is reported. The free energies of activation, thus obtained (12.4 to 14.3 kcal mol-1), were attributed to the conformational isomerization about the N-C bond. These barriers to rotation show solvent dependence in contrast to the tertiary analogues and are lower in free energy by ca. 2-3 kcal mol-1.