Substituent

About: Substituent is a research topic. Over the lifetime, 42877 publications have been published within this topic receiving 516716 citations. The topic is also known as: side chain & side group.

A Direct Catalytic Asymmetric Mannich-type Reaction via a Dinuclear Zinc Catalyst: Synthesis of Either anti- or syn-α-Hydroxy-β-Amino Ketones

Abstract: The use of imines bearing a hydrolyzable nitrogen substituent in direct asymmetric Mannich reactions with α-hydroxyketones is developed. Previous work focused on the use of N-arylimines or nonenolizable imines, and the latter with only methoxy-substituted α-hydroxyacetophenones. Using a dinuclear catalyst devised from 2,6-di-(S)-2‘-diphenylhydroxymethylpyrrolidino-N-methyl)-4-methylphenol and diethylzinc, a broad array of hydroxyacetylated aromatics, including phenyl, 2-furyl, 1-naphthyl, and 2-naphthyl, react well. In addition, the reactions focused on the use of enolizable imines. With the N-diphenylphosphinoyl, the reactions are anti selective with enantiomeric excesses ranging from 83 to 99%, except for the reaction of the 2-methoxy-2‘-hydroxyacetylbenzene. With the N-Boc-imines, the reactions were syn selective with enantiomeric excesses from 90 to 94%. The dependence of the diastereoselectivity on the nature of the N-substituent presumably arises from the steric demands of the diphenylphosphinoyl group.

Calix[4]pyrroles containing deep cavities and fixed walls. Synthesis, structural studies and anion binding properties of the isomeric products derived from the condensation of p-hydroxyacetophenone and pyrrole.

Abstract: The acid-catalyzed condensation of 4-hydroxyphenylmethyl ketone (p-hydroxyacetophenone) with pyrrole affords a new type of calix[4]pyrrole derivative that contains deep cavities and fixed walls. These new systems, which can be readily converted into the corresponding 4-methoxyphenyl species, can exist in the form of four different configurational isomers, as well as in different conformational forms. Three of the configurational isomers, namely the ????, ????, and ???? isomers, where the terms “?” and “?” indicate whether the bulky functionalized phenyl substituent faces “up” or “down” relative to the mean calixpyrrole plane, were isolated by column chromatography. Proof of structure and assignment of configuration was then effected using X-ray diffraction analysis. The affect of the meso-aryl substituent on the anion binding affinity of the receptor was investigated in solution (acetonitrile-d3:D2O; 99.5:0.5 v./v.) using standard 1H NMR titration techniques. Surprisingly, it was found that both the 4-hydroxyphenyl- and 4-methoxyphenyl-derived systems show lower affinities for small anions, viz. Cl-, and H2PO4-, than do simple unsubstituted calix[4]pyrroles such as meso-octamethylcalixpyrrole. On the other hand, increased selectivities and other binding effects ascribable to the ‘walls’ of the cavities were observed.

Substituent position effect on the properties of isomeric photochromic diarylethenes bearing chlorine atoms

Abstract: Three new isomeric photochromic diarylethenes, namely 1,2-bis[2-methyl-5-(4-chlorophenyl)-3-thienyl]perfluorocyclopentene (1o), 1,2-bis[2-methyl-5-(3-chlorophenyl)-3-thienyl]perfluorocyclopentene (2o), and 1,2-bis[2-methyl-5-(2-chlorophenyl)-3-thienyl]perfluorocyclopentene (3o) which bear two chlorine atoms at the para-, meta-, and ortho-position of both terminal phenyl groups, have been synthesized. The substituent position effect of chlorine atoms on their optoelectronic properties, including photochromic behavior and fluorescence, both in solution and in PMMA amorphous film, and electrochemical properties were investigated in detail. The results elucidated that the chlorine atoms and their substituent positions had a significant effect on the optoelectronic properties of these compounds. These diarylethene derivatives bearing two chlorine atoms have shown good photochromic behavior and fluorescent switching both in solution and in PMMA film. For diarylethenes 1–3, the cycloreversion quantum yields were gradually increased when the chlorine atom was attached to the para-, meta- and ortho-positions of the two terminal benzene rings; but, their absorption maxima, cyclization quantum yields and the molar absorption coefficients both of their open-ring and closed-ring isomers were remarkably decreased one by one. Furthermore, the clear oxidation waves of diarylethenes 1c, 2c and 3c were observed at 1.01, 0.92 and 0.98 V by performing the cyclic voltammograms experiments.

Mechanistic Study of the Oxidative N-Dealkylation Reactions of Bis(μ-oxo)dicopper Complexes

Abstract: The results of experiments designed to probe the mechanism by which the bis(μ-oxo)dicopper complexes [(LCu)2(μ-O)2](ClO4)2 (L = 1,4,7-tribenzyl-, 1,4,7-triisopropyl-, and 1,4-diisopropyl-7-benzyl-1,4,7-triazacyclononane ligands; LBn3, LiPr3, and LiPr2Bn, respectively) decompose to products arising from macrocyclic ligand N-dealkylation are described. After removal of copper from the decomposed solutions, analysis of the organic products revealed N-dealkylated ligands and aldehyde or ketone, the oxygen atoms in the latter being derived from the bis(μ-oxo)dicopper core as shown by 18O-isotope labeling experiments. Thus, the overall N-dealkylation is akin to monooxygenase reactions carried out by various metalloenzymes such as cytochrome P450, dopamine β-monooxygenase, and peptidyl glycine α-amidating monooxygenase. Direct, intramolecular attack of the bis(μ-oxo)dicopper core at a ligand substituent C−H bond during the rate-determining step was indicated by the observed first-order kinetics, the results of H...