Tandem transesterification and intramolecular cycloaddition of alpha-methoxycarbonylnitrones with chiral acyclic allyl alcohols: systematic studies on the factors affecting diastereofacial selectivity of the cycloaddition

DFT Study of Regio- and Stereoselective 13DC Reaction between Diazopropane and Substituted Chalcone Derivatives: Molecular Docking of Novel Pyrazole Derivatives as Anti-Alzheimer's Agents

In the present work, a combination of experimental and density functional theory (DFT) investigation of the (3+2) cycloaddition reactions of diazopropane with chalcone derivatives was reported. All calculations were performed using several DFT approaches (B3LYP, M06, M06-2X) and 6-311+G(d, p) basis set. Based on the NMR, MS analyses and IRC calculations, the pyrazole derivatives are the kinetic adducts over the oxadiazoles. The use of two equivalents of diazopropane leads to thermodynamical products. A molecular docking analysis was performed to investigate the efficiency of the obtained products against selected drug targets in anti-Alzheimer ligand-receptor interactions. We revealed that the ligands selected were bound mainly to the catalytic (CAS) and peripheral (PAS) anionic sites of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) inhibitors, respectively. The selected ligands 1, 3, 4 and P14 may act as the best inhibitors against Alzheimer's disease (AD).

Regio- and stereoselectivity of the [3+2] cycloaddition of nitrones with methyl-acetophenone: A DFT investigation

A theoretical study of the regio- and stereoselectivities of the [3 + 2] cycloaddition reactions of nitrones with substituted alkene (methyl acetophenone) is investigated using density functional theory (DFT) and carried out at B3LYP/6-311+G(d,p) level. The reactivity of these cycloadditions is rationalized by FMO model, activation energy calculations, and philicity indexes. The electronic populations have been calculated from natural orbital, which based on charges by using NBO analysis, MK and CHelpG electrostatic population. The four possible pathways, fused and bridged regioisomeric modes, and the two stereoisomeric approaches endo and exo for the cycloaddition reactions are analyzed and discussed. Analysis of TS geometries and bond lengths demonstrate that these reactions follow a one-step mechanism with asynchronous transition states. The activation energy indicated a favored endo approach along the four reaction pathways.

The Chemistry of Pericyclic Reactions and Their Application to Syntheses of Heterocyclic Compounds

Diels-Alder reactions of benzylidenecyanomethyl-1,3-benzothiazoles 17 and -1,3-benzoxazoles 18 as 1-aza-1,3-butadienes are described. The dienes 17 and 18 featuring stabilized imine moieties in the form of heteroaromatic rings react with both electron-deficient and electron-rich dienophiles to give corresponding cycloadducts regioselectively. The cycloadditions of the intramolecular systems 34c,d and 35c,d proceeded smoothly via the exo-transition state, stereoselectively affording polycyclic compounds 36c,d and 37c,d in good to excellent yields. The diene systems of 17 and 18 were extended to dienes 19a-c with ester groups at diene-4-positions. Dienes 19a-c exhibited high Diels-Alder reactivities with electron-rich alkenes. Dienes 19a-c also reacted with allyl alcohols 55-58 in the presence of stanoxane catalyst 53 to give cycloadducts 59-62 via transesterification and intramolecular cycloaddition. Although alpha-alkoxycarbonylnitrones 64 have been very attractive nitrones for the syntheses of amino acids, the nitrones 64 exist as equilibrating mixtures of (E)-64 and (Z)-64. To solve this problem, three methods were explored: 1) sequential transesterification and intermolecular cycloaddition of nitrones 64 with allyl alcohols; 2) use of chiral and geometry-fixed nitrone 84; and 3) selective activation of (Z)-64 by Eu(fod)3. These methods were applied to syntheses of nikkomycins, clavalanine, and beta-substituted alpha-amino acids. The reactions of photoinduced carbonyl ylides from alpha,beta-unsaturated gamma,delta-epoxy nitriles were studied. Direct irradiation (lambda = 254 nm) of (E)-129 led selectively to products arising from the carbonyl ylide XXV or the carbene intermediate XXVI. The carbonyl ylides generated from (E)-129, (E)-139, and (Z)-143 were trapped with MeOH in the presence of amine, affording the corresponding acetals in moderate yields (Schemes 42 and 43). Photocyclization reactions of delta-hydroxyalkyl epoxy nitriles 148a-e led to spiro acetals arising from the carbonyl ylides (Scheme 45). The photoinduced carbonyl ylides from the epoxy dinitriles 158 and 160-163 underwent 1,3-dipolar cycloaddition with enol ethers, leading to a tetrahydrofuran system (Schemes 49 and 50, Table 14). Electrocyclization of 3-butadienylindoles 184 to intermediary dihydrocarbazoles XXXII followed by elimination of MeOH gave 3-oxyganated carbazoles 185, which were transformed to carbazole alkaloids hyellazole 168, 4-demethoxycarbazomycin B 170 and carazostatin 171, respectively. Claisen rearrangement of 3-(1-amino-1-vinyloxy) indolines derived from 3-hydroxyindolines 192 and amide acetal 193 gave indol-4-ylacetamides 194, which was reduced to afford 4-(2-aminoethyl) indoles 198, which has a framework of biologically active 4-substituted indole compounds. Claisen rearrangement of 3-allyloxyindoles produced in situ by condensation of indolin-3-ones 202 with allyl alcohols 203 and 206-211 gave 2-allylindolin-3-ones 204, 205 and 212-220. The domino reactions, Horner-Wadsworth-Emmons olefination of 2-allyloxyindole 233, isomerization, and Claisen rearrangement produced 3-allylindolin-2-one 234, which was derivatized to 3a-allylpyrrolo [2,3-b] indole alkaloid, flustramine C 221. Reverse aromatic Cope rearrangement of 2-allyl-3-indolidene acetonitriles 241-243, formed by Horner-Wadsworth-Emmons reaction of 2-allylindolin-3-ones 238-240, afforded indoles 244-246.

Intramolecular cycloadditions of alpha-allyloxycarbonylnitrones: stereoselective synthesis of 3-amino-2(5H)furanones

Treatment of furoisoxazolidines with NaH leads to functionalized 3-amino-2(5H)-furanones through a new rearrangement pattern of the isoxazolidine nucleus. This process has been usefully exploited for the synthesis of enantiomerically pure (5R)-3-alkylamino-5-methyl-2(5H)-furanones.