Substituent Effects in the Silylation of Secondary Alcohols: A Mechanistic Study

2018 ◽  
Vol 24 (56) ◽  
pp. 15052-15058 ◽  
Author(s):  
Marta Marin-Luna ◽  
Pascal Patschinski ◽  
Hendrik Zipse
Keyword(s):  
Substituent Effects ◽  
Mechanistic Study ◽  
Secondary Alcohols

A Unified Mechanism to Account for Manganese‐ or Ruthenium‐Catalyzed Nitrile α‐Olefinations by Primary or Secondary Alcohols: A DFT Mechanistic Study

2019 ◽  
Vol 25 (15) ◽  
pp. 3939-3949 ◽  
Author(s):  
Yu Lu ◽  
Ruihua Zhao ◽  
Jiandong Guo ◽  
Zheyuan Liu ◽  
Wasihun Menberu ◽  
...  
Keyword(s):  
Mechanistic Study ◽  
Secondary Alcohols

Regioselectivity of glycoluril-directed Claisen condensations — A kinetic and mechanistic study of substituent effects in the nucleophilic acyl group

2006 ◽  
Vol 84 (9) ◽  
pp. 1188-1196 ◽  
Author(s):  
Mei Chen ◽  
Katie Won ◽  
Robert S McDonald ◽  
Paul H.M Harrison
Keyword(s):  
Kinetic Data ◽  
Uv Spectroscopy ◽  
Substituent Effects ◽  
Reaction Rates ◽  
Quantitative Yield ◽  
Mechanistic Study ◽  
Claisen Condensation ◽  
Bond Forming ◽  
Rate Limiting

The Claisen-like condensation of a series of 1-arylacetyl-6-acetyl-3,4,7,8-tetramethylglycolurils (Ar = Ph, p-OMeC6H4, and p-ClC6H4) was studied in preparative experiments and by analysis of kinetic data. The reactions proceeded in virtually quantitative yield and were highly regioselective: the corresponding N-(2′-aryl-3′-ketobutanoyl)-3,4,7,8-tetramethylglycolurils were obtained in all cases, with none of the 4′-aryl regioisomers being detected. Clean bimolecular kinetics were observed for each conversion using UV spectroscopy. Reaction rates followed the order Ar = p-OMeC6H4 < Ph < p-ClC6H4. The results are explained by a mechanism in which the deprotonation of the substrates is rate-limiting; thus, deprotonation of the arylacetyl groups is favoured. The ensuing enolate reacts rapidly in the C–C bond-forming step.Key words: glycoluril, biomimetic, Claisen condensation, regioselectivity, kinetics, mechanism, substituent effects.

Mechanisms for the oxidation of secondary alcohols by dioxoruthenium(VI) complexes

1998 ◽  
Vol 76 (6) ◽  
pp. 919-928 ◽  
Author(s):  
Zhao Wang ◽  
W David Chandler ◽  
Donald G Lee
Keyword(s):  
Transition State ◽  
Isotope Effects ◽  
Substituent Effects ◽  
Secondary Alcohols ◽  
Benzyl Alcohols ◽  
Radical Intermediates ◽  
Oxidation Of Alcohols ◽  
Substituent Constants ◽  
Deuterium Isotope Effects ◽  
Rate Limiting

Possible mechanisms for the oxidation of alcohols by dioxoruthenium(VI) complexes are critically evaluated. Rate constants for the reduction of trans-[(TMC)RuVI(O)2]++ (TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) by substituted benzhydrols are correlated more satisfactorily with Hammett σ substituent constants ( rho = -1.44 ± 0.08, r2 = 0.98) than with σ + substituent constants ( rho = -0.72 ± 0.11, r2 = 0.83). Similar observations for the oxidation of substituted benzyl alcohols have recently been reported, confirming that the transition state for these reactions is not carbocation-like. Primary deuterium isotope effects indicate that cleavage of the α -C-H bond is rate-limiting. The lack of an observable O-D isotope effect and the ease of oxidation of ethers indicates that the presence of a hydroxyl is not essential. The previously reported observation that cyclobutanol is quantitatively converted into cyclobutanone by dioxoruthenium(VI) complexes eliminates free-radical intermediates from consideration as part of the mechanism, and negative entroπes of activation (-Δ Sdouble dagger = 96-137 J mol-1 K-1) suggest a structured transition state. Only two of eight possible reaction mechanisms considered were found to be consistent with the available data. A critical analysis of the available data indicates that a 2 + 2 (C-H + Ru font 35137 roman T O) addition and a reaction initiated by ligand formation through the interaction of the reductant's HOMO with the oxidant's LUMO are the most likely reaction mechanisms.Key words: oxidation, alcohols, ruthenium(VI), mechanism, substituent effects.

Unexpected Substituent Effects in the Iso-Heterocyclic Boulton–Katritzky Rearrangement of 3-Aroylamino-5-methyl-1,2,4-oxadiazoles: A Mechanistic Study

2019 ◽  
Vol 123 (46) ◽  
pp. 10004-10010
Author(s):  
Vincenzo Frenna ◽  
Paolo Lo Meo ◽  
Antonio Palumbo Piccionello ◽  
Domenico Spinelli
Keyword(s):  
Substituent Effects ◽  
Mechanistic Study

scholarly journals A Mechanistic Study on the Tautomerism of H-Phosphonates, H-Phosphinates and Secondary Phosphine Oxides

Molecules ◽  
2019 ◽  
Vol 24 (21) ◽  
pp. 3859 ◽  
Author(s):  
Daniella Vincze ◽  
Péter Ábrányi-Balogh ◽  
Péter Bagi ◽  
György Keglevich
Keyword(s):  
Molecular Descriptors ◽  
Substituent Effects ◽  
Building Blocks ◽  
Mechanistic Study ◽  
Secondary Phosphine ◽  
Phosphine Oxides ◽  
Dft Methods ◽  
Implicit Solvents ◽  
Different Levels ◽  
P Ligands

H-phosphonates, H-phosphinates and secondary phosphine oxides may be preligands, and are important building blocks in the synthesis of pharmaceuticals, pesticides, and P-ligands. The prototropic tautomerism influenced by substituent effects plays an important role in the reactivity of these species. The main goal of our research was to study the tautomerism of the >P(O)H reagents by means of computational investigations applying several DFT methods at different levels. We focused on the effect of implicit solvents, and on explaining the observed trends with physical chemical molecular descriptors. In addition, multiple reaction pathways incorporating three P-molecules were elucidated for the mechanism of the interconversion.

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