Search results for "Selectivity"

A Next‐Generation Air‐Stable Palladium(I) Dimer Enables Olefin Migration and Selective C−C Coupling in Air

2020

Abstract We report a new air‐stable PdI dimer, [Pd(μ‐I)(PCy2 tBu)]2, which triggers E‐selective olefin migration to enamides and styrene derivatives in the presence of multiple functional groups and with complete tolerance of air. The same dimer also triggers extremely rapid C−C coupling (alkylation and arylation) at room temperature in a modular and triply selective fashion of aromatic C−Br, C−OTf/OFs, and C−Cl bonds in poly(pseudo)halogenated arenes, displaying superior activity over previous PdI dimer generations for substrates that bear substituents ortho to C−OTf.

Stereoselective 1,3-Dipolar Cycloadditions of a Chiral Nitrone Derived from Erythrulose. An Experimental and DFT Theoretical Study

2000

We have investigated several 1,3-dipolar cycloadditions of a chiral nitrone prepared from L-erythrulose. While cycloadditions to carbon-carbon multiple bonds of dipolarophiles such as ethyl acrylate, ethyl propiolate, or dimethyl acetylenedicarboxylate were poorly stereoselective, reaction with acrylonitrile provided predominantly one diastereomeric adduct. Furthermore, the regioselectivity exhibited by the two structurally similar dipolarophiles ethyl acrylate and ethyl propiolate was found to be opposite. The molecular mechanisms of these cycloadditions have thus been investigated by means of density functional theory (DFT) methods with the B3LYP functional and the 6-31G and 6-31+G basis …

ChemInform Abstract: Regiospecific and Stereoselective Ene Reaction of the A-Ring Methylcyclohexene Moiety of Polycyclic Terpenoid Systems with Dimet…

2010

Cycloaddition Reactions with Vinyl Heterocycles

1995

Publisher Summary The Diels-Alder reaction is one of the most common and elegant methods for the construction of six-membered rings. Although the number of Diels-Alder cycloadditions with open-chain and alicyclic dienes is very large, the number of examples with aromatic heterocyclic compounds is relatively small. The introduction of a vinyl group as a substituent onto a heterocycle increases the number of possible reactions. This new possibility, however attractive for synthetic purposes, is successful only with π-excessive five-membered heterocyclic derivatives with a few exceptions. The chapter discusses the reactions of vinyl heterocycles with carbodienophiles. The endocyclic and exo-en…

Regiospecific and stereoselective ene reaction of the A-ring methylcyclohexene moiety of polycyclic terpenoid systems with dimethyl acetylenedicarbox…

2001

Polycyclic terpenoid compounds with a methylcyclohexene moiety at the A-ring, such as 1 and 7, give a regio- and stereoselective ene reaction when heated at low temperatures with dimethyl acetylenedicarboxylate. The structure and stereochemistry of the compound formed in the case of 1, e.g. 5, is determined by X-ray analysis.

Transport of dipeptides and phosphono dipeptides through an immobilized liquid membrane. Stereoselectivity of the process

1993

Abstract Dipeptide and phosphono dipeptide hydrochlorides permeated well through a 1-decanol membrane supported in a porous polyethylene hollow fiber matrix. This transfer is easily accomplished either by passive or by carrier-facilitated (with Kryptofixes 222 or 5 present in the membrane phase) transport. The transport is stereoselective with l-l dipeptides being transported faster than their l-d isomers.

Cyclocarbonylation reactions of allylphenols and allylnaphthols catalyzed by Pd/C- 1,4-bis(diphenylphosphine)butane

2002

Palladium/activated carbon (Pd/C) in the presence of 1,4-bis(diphenylphosphino)butane is an efficient heterogeneous catalyst for cyclocarbonylation reactions of 2-allyl phenols affording five-, six-, and seven-membered ring lactones. Various examples of cyclocarbonylation are reported and the regioselectivity is compared with the homogeneous system. Both commercial Pd/C and Pd/C prepared from activated carbons obtained from vegetable and polymeric wastes are investigated.

A theoretical study on the regioselectivity of 1,3-dipolar cycloadditions using dft-based reactivity indexes

2004

The regioselectivity for a series of four 1,3-dipolar cycloaddition reactions has been studied using global and local reactivity indexes. The results of the theoretical analysis suggest that for asynchronous cycloadditions associated to polar processes, the regioselectivity is consistently explained by the most favorable two-center interactions between the highest nucleophilic and electrophilic sites of the reagents.

Mentor – A Trustee for Disadvantaged Youth

2015

<p><em><span lang="EN-GB">The perception of oneself and the surrounding environment are developed during childhood. The behaviour of others directly influences the attitude towards oneself and decisions and observations about one`s value. One of the biggest deficiencies of institutional out-of-family care that significantly hinders the comprehensive development of children is the inability of children to form close bonds with adults. To come to a conclusion that you are not loved and worthless means the feel of deep disappointment. The child becomes shore that he has been deceived and abandoned. These thoughts evoke protests, depression, and insecurity. Due to these miscon…

Lanthanum-pyBOX complexes as catalysts for the enantioselective conjugate addition of malonate esters to β,γ-unsaturated α-ketimino esters

2018

[EN] In this paper, we report the application of chiral complexes of La(III) with pyBOX ligands as Lewis acid catalysts in the conjugate addition of malonic esters to N-tosyl imines derived from ß,gamma-unsaturated alfa-keto esters to give the corresponding chiral alfa,ß-dehydroamino esters. pyBOX complexes with La(III), Yb(III), Sc(III), and In(III) triflates were assessed in this reaction but only La(III) showed good activity and enantioselectivity, while Yb(III) provided the expected product with low yield and stereoselectivity, and the Sc(III) and In(III) complexes were completely inactive. The complex of La(OTf)3 with the diphenyl-pyBOX ligand prepared in situ provided the best results…