Influence of Steric Crowding on Diastereoselective Arabinofuranosylations.

The occurrence of arabinofuranosides on the cell surface of Mycobacterium tuberculosis (Mtb) and their significance in controlling disease spurred interest in developing strategies for their diastereoselective synthesis. Mtb uses enzymes to achieve diastereoselectivity through noncovalent interactions. Of the two possible glycosidic linkages, chemically, 1,2-trans linkage is relatively easy to synthesize by taking advantage of neighboring group participation, whereas synthesis of the 1,2-cis linkage is notoriously difficult. In this article, stereochemical effects on the diastereoselectivity of arabinofuranosidation are investigated with thiopyridyl, imidate, and thiotolyl donors as well as differently crowded glycosyl acceptors; subtle differences in the stereochemical environment of the acceptors were observed to alter the diastereoselectivity of the furanoside formation. Results from this endeavor suggest that 1,2-cis arabinofuranosides can be synthesized conveniently by conducting the reaction at lower temperature on sterically demanding and less reactive substrates.

Energy decomposition analysis of cation-π, metal ion-lone pair, hydrogen bonded, charge-assisted hydrogen bonded, and π-π interactions.

This study probes the nature of noncovalent interactions, such as cation-π, metal ion-lone pair (M-LP), hydrogen bonding (HB), charge-assisted hydrogen bonding (CAHB), and π-π interactions, using energy decomposition schemes-density functional theory (DFT)-symmetry-adapted perturbation theory and reduced variational space. Among cation-π complexes, the polarization and electrostatic components are the major contributors to the interaction energy (IE) for metal ion-π complexes, while for onium ion-π complexes (NH4+, PH4+, OH3+, and SH3+) the dispersion component is prominent. For M-LP complexes, the electrostatic component contributes more to the IE except the dicationic metal ion complexes with H2 S and PH3 where the polarization component dominates. Although electrostatic component dominates for the HB and CAHB complexes, dispersion is predominant in π-π complexes.

Gold(I)-catalyzed unprecedented rearrangement reaction between 2-aminobenzaldehydes with propargyl amines: an expedient route to 3-aminoquinolines.

Access to aminoquinolines: a gold(I)-catalyzed unprecedented rearrangement reaction between 2-aminobenzaldehydes with propargyl amine was studied. The study provided, for the first time, direct access to 3-aminoquinolines in one step starting from readily available starting materials. Elegantly designed experiments were employed to unravel the mechanism of this unprecedented rearrangement, which are corroborated by DFT calculations.

Estimating regio and stereoselectivity in [4+2] cycloadditions of vinyl-substituted cyclic dienes with maleic anhydride.

Density functional theory calculations are performed to examine the regio and stereoselective preferences in [4+2] cycloaddition reactions of vinyl cyclopentadiene (1 and 2) and vinyl heterocyclic (1-N, 1-O, 1-S, 2-N, 2-O and 2-S) systems with maleic anhydride. Stepwise and concerted pathways of model systems 1 and 2 as dienes with ethylene as dienophile reveal that the reactions proceed through asynchronous and concerted pathway. 3-Vinyl systems (2) are predicted to be more reactive compared to 2-vinyl systems (1). The regio and stereoselective preferences are evaluated based on activation energies, reaction energies, density functional based descriptors and atoms in molecules analysis. In all cases, extra-annular cycloadducts are more feasible compared to intra-annular cycloadducts. Stereoselectivity depends on the favorable secondary orbital interactions. Solvents such as water, tetrahydrofuran, acetone, and dimethyl sulphoxide are employed to understand the effects of solvents on the cycloadduct formation. The computational results thus obtained are compared with the earlier experimental observations that are available.

Further shortening of the C-C single bond in substituted tetrahedranyl tetrahedrane systems: an energy decomposition analysis.

The computational study explores the electronic fine tuning of the exocyclic C-C single bond length in tetrahedranyl tetrahedrane as a function of various substituents. The factors which determine the bond lengths and bond strengths are examined by using the EDA method.