Search results for "Regioselectivity"
showing 10 items of 298 documents
1,3-Dipolar cycloaddition of 1H-pyrazinium-3-olate and N1- and C-methyl substituted pyrazinium-3-olates with methyl acrylate: a density functional th…
2011
Abstract A DFT study of the 1,3-dipolar cycloaddition of methyl acrylate to 1H-pyrazinium-3-olate and N1- and C-methyl substituted pyrazinium-3-olates, in the gas phase and in THF, has been carried out at the B3LYP/6-31G(d) level. Two stereoisomeric pathways, endo and exo, and two regioisomeric channels, 2-oxo-3,8-diazabicyclo[3.2.1]octane-6-ester and 7-ester products, have been considered. Thermodynamic and kinetic parameters calculated at room temperature have been analyzed. The regioselectivity has been interpreted using reactivity indices. It is generally found that the exo pathway is preferred and the formation of the 6-esters is dominant. The theoretical data obtained for the cycloadd…
Palladium-Catalyzed Dehydrogenative β’-Arylation of β-Keto Esters under Aerobic Conditions: Interplay of Metal and Brønsted Acids
2012
The Bronsted aids: The first dehydrogenative arylation of β-keto esters with arenes under ambient aerobic conditions is described. Under a Pd(II)/Bronsted acid co-catalytic system, regioselective arylations with alkoxylated arenes and phenols were achieved in good yields, even in gram-scale conditions.
Synthesis of silacyclopent-2-en-4-ols via intramolecular [2 + 2] photocycloaddition of benzoyl(allyl)silanes
2019
Organosilicon compounds are versatile units with a wide range of uses from medicinal chemistry to the field of organic electronics. An unprecedented method for the synthesis of novel diaryl-substituted silacyclopentenols via blue-light promoted intramolecular [2 + 2] photocycloaddition of acyl silanes is herein disclosed. Additionally, the present findings demonstrate the influence of the olefin substituents in controlling the regioselectivity of the intramolecular Paterno–Buchi reaction, providing silacycles different from previously reported ones. The high degree of functionalization of these compounds makes them attractive precursors to other synthetically challenging silacyclopentanes.
Stereoselective synthesis and application of tridentate aminodiols derived from (+)-pulegone
2016
Abstract A library of tridentate aminodiols, derived from naturally occurring (R)-(+)-pulegone, was synthesized and applied as chiral catalysts in the addition of diethylzinc to benzaldehyde. The reduction of pulegone furnished pulegol, which was transformed into allylic trichloroacetamide via Overman rearrangement of the corresponding trichloroacetimidate. The protected enamine was subjected to dihydroxylation with OsO4/NMO system resulting in a 1:1 mixture of (1R,2R,4R)- and (1S,2S,4R)-aminodiol diastereomers. After the removal of the trichloroacetyl protecting groups, the obtained primary aminodiols were transformed into secondary ones. The regioselectivity of the ring closure of the N-b…
Semisynthesis of the Antiviral Abietane Diterpenoid Jiadifenoic Acid C from Callitrisic Acid (4-Epidehydroabietic Acid) Isolated from Sandarac Resin
2014
The semisynthesis of the antiviral abietane diterpenoid (+)-jiadifenoic acid C starting from the available methyl ester of callitrisic acid (4-epidehydroabietic acid) isolated from sandarac resin is reported. A protocol for the isolation of methyl callitrisate (methyl 4-epidehydroabietate) in gram quantities from sandarac resin is also described. Allylic C-17 oxygenation was introduced by regioselective dehydrogenation of the isopropyl group of methyl callitrisate with DDQ followed by selenium-catalyzed allylic oxidation. Ester hydrolysis afforded (+)-jiadifenoic acid C in 22% overall yield from methyl callitrisate. This semisynthetic route provides a convenient source of this anti-Coxsacki…
Carborane-stilbene dyads: influence of substituents and cluster isomers on the photoluminescence properties
2017
Two novel styrene-containing meta-carborane derivatives substituted at the second carbon cluster atom (Cc) with either a methyl (Me), or a phenyl (Ph) group, are introduced herein alongside with a new set of stilbene-containing ortho- (o-) and meta- (m-) carborane dyads. The latter set of compounds has been prepared from styrenecontaining carborane derivatives via Heck coupling reaction. High regioselectivity has been achieved for these compounds by using a combination of palladium complexes [Pd2(dba)3]/[Pd(t-Bu3P)2] as a catalytic system, yielding exclusively E isomers. All compounds have been fully characterized and the crystal structures of seven of them analyzed by X-ray diffraction. Th…
Selective Derivatization of Calix[4]arenes via Amino Groups Attached to the Wide Rim
2004
A new strategy is proposed for the synthesis of tetraether derivatives of calix[4]arenes bearing at the wide rim nitro and phthalimido groups in well defined positions. Since both groups are precursors of amino functions, calix[4]arenes substituted by different N-acylamino residues are easily available in four steps. The essential steps during the synthesis of the precursor consist in the protection of amino groups by the formation of their phthalimides followed by ipso-nitration of the remaining tert-butylphenol ether units. This nitration occurs without side reactions at the phthalimido substituted units, in contrast to simple N-acyl derivatives.
Efficient Synthesis of Multifunctional Chelating Agents Based on Tetraazacycloalkanes
2018
An efficient route has been developed for the synthesis of multifunctional tetraazacycloalkanes (in particular 1,4,7,10-tetraazacyclotridecane) incorporating an aminomethyl pendant arm on the carbon skeleton. Starting from the appropriate C-functionalized bisaminal-protected intermediate, the target macrocycles were easily obtained by means of a step-by-step introduction of the desired functional groups onto the free primary amine group, followed by deprotection of the bisaminal intermediates. This straightforward and versatile synthetic approach paves the way for the design of a new family of multifunctional chelators.
Synthesis of Densely Functionalised 5-Halogen-1,3-oxazin-2-ones byHalogen-Mediated Regioselective Cyclisation of N-Cbz-ProtectedPropargylic Amines: A…
2013
A very efficient synthesis of 5-halogen-1,3-oxazin-2-ones has been accomplished by the halocyclisation reaction of chiral nonracemic N-carbobenzyloxy (N-Cbz)-protected propargylic amines by using I-2, Br-2 and Cl-2 as electrophile sources. The nature of the halogen influences the reaction time and yield. However, in all cases the reaction is totally regioselective taking place through a 6-endo-dig process regardless of the nature of the halogen and of the substituents in the starting material. To rationalise the experimental results, theoretical studies at the B3LYP/6-311G* level have been performed.
On the mechanism of the addition of organolithium reagents to cinnamic acids
2001
Abstract The regioselectivity of the addition of tert-butyllithium to cinnamic acid is subject to reaction conditions and to substituent electronic effects. Significant effects are observed in the presence of several additives including a radical trap such as α-methylstyrene. Competition experiments by addition of the organolithium reagent to mixtures of substituted cinnamic acids show that the relative rates of both conversion of the starting acids and formation of the 1,3-adducts are subject to electronic effects, whereas rates for 1,4-addition are independent of the substituents. These features are in agreement with a polar addition mechanism, but a fast SET equilibrium followed by slow …