Search results for "chemoselectivity"

First Principles Calculations for Hydrogenation of Acrolein on Pd and Pt: Chemoselectivity Depends on Steric Effects on the Surface

2016

The chemoselective hydrogenation of acrolein on Pt(111) and Pd(111) surfaces is investigated employing density functional theory calculations. The computed potential energy surfaces together with the analysis of reaction mechanisms demonstrate that steric effects are an important factor that governs chemoselectivity. The reactions at the C=O functionality require more space than the reactions at the C=C functionality. Therefore the formation of allyl alcohol is more favorable at low coverage, while the reduction of the C=C bond and the formation of propanal becomes kinetically more favorable at higher coverage. The elementary reaction steps are found to follow different reaction mechanisms,…

Green Oxidation of Alcohols to Carbonyl Compounds by Heterogeneous Photocatalysis

2010

Halogen‐Imparted Reactivity in Lithium Carbenoid Mediated Homologations of Imine Surrogates: Direct Assembly of bis‐Trifluoromethyl‐β‐Diketiminates a…

2020

The selective formal insertion (homologation) of a carbon unit bridging the two trifluoroacetamidoyl chlorides (TFAICs) units is reported. The tactic is levered on a highly chemoselective homologation-metalation-acyl nucleophilic substitution sequence which precisely enables to assemble novel trifluoromethylated β-diketiminates within a single synthetic operation. Unlike previous homologations conducted with LiCH2Cl furnishing aziridines, herein we exploit the unique capability of iodomethyllithium to act contemporaneously as a C1 source (homologating effect) and metalating agent. The mechanistic rationale grounded on experimental evidences supports the hypothesized proposal and, the struct…

Mixed Dialkylaluminum Chlorides and Mixed Trimethylorganoaluminates in Chemoselective 1,4 Addition Reactions to Alkylidene Malonic Acid Diethyl Ester

2000

Mixed alkyl-methyl- and aryl-methylorganoaluminum chlorides 6 were formed by reaction of methylaluminum dichloride with organolithium or Grignard compounds and used for chemoselective 1,4 addition of higher alkyl, aryl, alkenyl and alkinyl groups to alkylidine malonic esters 1 and 2. As an alternative, mixed trimethylorganoaluminates 7 can also be applied for these Michael addition reactions. For conjugate addition of alkenyl groups to alkylidene malonates 1 and 2, alkenyl diisopropylalanes 10 obtained from alkynes and diisopropylaluminum hydride proved the most efficient reagents. Using these novel mixed organoaluminum compounds, β-branched malonic (carboxylic) acid derivatives 3c, 8, 9 an…

A theoretical study of the selectivity for the domino [5+2]/[4+2] cycloadditions of γ-pyrones bearing tethered alkenes with substituted 1,3-butadienes

2001

Abstract Selectivity of the domino [5+2]/[4+2] cycloaddition reactions of a β-silyloxy-γ-pyrone bearing a tethered alkene with two substituted 1,3-butadienes have been theoretically studied at the B3LYP/6-31G∗//AM1 and B3LYP/6-31G∗ computational levels. Analysis of these results allow explaining the regio, stereo and chemoselectivity observed experimentally at these domino reactions. Selectivity outcome is reproduced by these calculations.

ChemInform Abstract: A Theoretical Study of the Selectivity for the Domino [5 + 2]/[4 + 2] Cycloadditions of γ-Pyrones Bearing Tethered Alkenes with …

2010

Abstract Selectivity of the domino [5+2]/[4+2] cycloaddition reactions of a β-silyloxy-γ-pyrone bearing a tethered alkene with two substituted 1,3-butadienes have been theoretically studied at the B3LYP/6-31G∗//AM1 and B3LYP/6-31G∗ computational levels. Analysis of these results allow explaining the regio, stereo and chemoselectivity observed experimentally at these domino reactions. Selectivity outcome is reproduced by these calculations.

A molecular electron density theory study of the mechanism, chemo- and stereoselectivity of the epoxidation reaction of R -carvone with peracetic acid

2019

The epoxidation reaction of R-carvone 8 with peracetic acid 9 has been studied within the molecular electron density theory at the B3LYP/6-311(d,p) computational level. The chemo- and stereoisomeric reaction paths involving the two C–C double bonds of R-carvone 8 have been studied. DFT calculations account for the high chemoselectivity involving the C–C double bond of the isopropenyl group and the low diastereoselectivity, in complete agreement with the experimental outcomes. The Baeyer–Villiger reaction involving the carbonyl group of R-carvone 8 has also been analysed. A bonding evolution theory analysis of the epoxidation reaction shows the complexity of the bonding cha…

A new and expeditious strategy for the synthesis of β-amino acids from Δ2-oxazolines

2001

Abstract A new, mild two-step synthesis of racemic β-amino acids starting from 2-alkyl-Δ2-oxazolines is described. The process implies the initial formation of masked N-substituted or N-unsubstituted β-enamino acid derivatives followed by chemoselective reduction of the enamino moiety. The process takes place with high yields, total chemoselectivity and moderate diastereoselectivity.

Synthesis of 1,3,5-Trisubstituted Hydantoins by Regiospecific Domino Condensation/Aza-Michael/O→N Acyl Migration of Carbodiimides with Activated α,β-…

2005

[reaction: see text] Carbodiimides and suitably activated alpha,beta-unsaturated carboxylic acids react effectively to afford a vast array of 1,3,5-trisubstituted hydantoins by means of a regiospecific domino condensation/aza-Michael/N--O acyl migration. The reaction works well in very mild conditions (20 degrees C, dichloromethane) with fumaric acid derivatives bearing an electron-withdrawing group in the beta position. Good results have been obtained also with less activated substrates bearing only one electron-withdrawing group in the beta position, using more polar solvents (acetonitrile, DMF), and in the presence of a base (2,4,6-trimethylpyridine). Reactions with asymmetric carbodiimi…

A density functional theory study of the chemoselectivity and regioselectivity of the domino cycloaddition reactions of nitroalkenes with substituted…

2000

The chemoselectivity and regioselectivity of the domino intermolecular [4 + 2]/[3 + 2] cycloaddition reactions of nitroalkenes with substituted alkenes, vinyl ethers as electron-rich alkenes and vinyl ketones as electron-poor alkenes, have been studied using density functional theory (DFT) methods with the B3LYP functional and the 6-31G* basis set. These domino processes comprise two consecutive cycloaddition reactions: the first one is an intermolecular [4 + 2] cycloaddition of the vinyl ether to the nitroalkene to give a nitronate intermediate, which then affords the final nitroso acetal adduct through an intermolecular [3 + 2] cycloaddition reaction with the vinyl ketone. The two consecu…