Detection and kinetic characterization of SNV intermediates. Reactions of thiomethoxybenzylidene Meldrum's acid with thiolate ions, alkoxide ions, OH-, and water in aqueous DMSO

1999 ◽  
Vol 77 (5-6) ◽  
pp. 584-594 ◽  
Author(s):  
Claude F Bernasconi ◽  
Rodney J Ketner ◽  
Xin Chen ◽  
Zvi Rappoport
Keyword(s):  
Rate Constants ◽  
Nucleophilic Addition ◽  
Equilibrium Constants ◽  
Intrinsic Rate ◽  
Nucleophilic Attack ◽  
Meldrum's Acid ◽  
Meldrum’S Acid ◽  
Nucleophilic Vinylic Substitution ◽  
Steady State Levels ◽  
Vinylic Substitution

The reaction of thiomethoxybenzylidene Meldrum's acid (5-SMe) with thiolate and alkoxide ion nucleophiles is shown to proceed by the two-step addition-elimination SNV mechanism in which the tetrahedral intermediate accumulates to detectable levels. For the reactions with thiolate ions, rate constants for nucleophilic addition (k1RX), its reverse (k-1RX), and for conversion of the intermediate to products (k2RX) were determined. For the reactions with alkoxide ions, only k1RX and k-1RX could be obtained; the intermediate in these reactions did not yield the expected substitution products, and hence no k2RX values could be determined. The reactions with OH- and water are believed to follow the same mechanism, but the respective intermediates remain at steady-state levels, and only k1OH and k1H²O for nucleophilic attack on 5-SMe were measurable. New insights regarding structure-reactivity behavior in SNV reactions are gained from comparisons of rate and equilibrium constants in the reactions of 5-SMe with the corresponding parameters in the reactions of methoxybenzylidene Meldrum's acid (5-OMe) and benzylidene Meldrum's acid (5-H). In particular, the relative importance of steric and pi-donor effects of the MeS vs. MeO group in 5-SMe and 5-OMe, respectively, and their role in affecting the intrinsic rate constants for nucleophilic addition, has been clarified by these comparisons. Our results also add support to a previous suggestion that soft-soft type interactions tend to increase intrinsic rate constants for thiolate ion addition to vinylic substrates, especially 5-SMe with the soft MeS group.Key words: nucleophilic vinylic substitution, intrinsic rate constants, transition state imbalances, steric/pi-donor/anomeric effects.

Reactions of α-isobutyl-α-(methylthio)methylene Meldrum's acid with primary amines in aqueous DMSO

2006 ◽  
Vol 84 (12) ◽  
pp. 1679-1685 ◽  
Author(s):  
Supriya Biswas ◽  
Mahammad Ali ◽  
Zvi Rappoport ◽  
Hatim Salim
Keyword(s):  
Second Order ◽  
Base Catalysis ◽  
Primary Amines ◽  
Meldrum's Acid ◽  
Meldrum’S Acid ◽  
Amine Concentration ◽  
First Order ◽  
Acid Base Equilibrium ◽  
Vinylic Substitution ◽  
Step Mechanism

The aminolysis of α-isobutyl-α-(methylthio)methylene Meldrum's acid 7 with primary amines, namely, n-butylamine, glycinamide, and methoxyethylamine in DMSO–H2O (50:50, v/v) at 20 °C is overall second-order but first-order in both 7 and amines. The reaction with aminoacetonitrile (AA) is overall third-order, first-order in substrate, and second-order in amine at low amine concentration, while at high amine concentration and high pH the dependence on amine is first-order. A general three-step mechanism has been proposed for all these reactions. For the former group of amines, the first step is a rate-limiting attack of the amine to form the tetrahedral intermediate (TA±), followed by a fast acid–base equilibrium and a fast RNH3+- or H2O-assisted leaving group expulsion. For AA, general base catalysis was confirmed from the dependence of kA on [AA]f and on [OH–]. For all four amines, a good Brønsted plot of log k1 vs. pKaAH in DMSO–H2O (50:50, v/v) with βnuc = 0.34 ± 0.02 was observed. These observations are consistent with the suggested mechanism.Key words: nucleophilic vinylic substitution reactions, primary amines, α-isobutyl-α-(methylthio)methylene Meldrum's acid, three-step mechanism.

An Expeditious One-Pot Three-Component Synthesis of 4-Aryl-3,4-dihydrobenzo[g] quinoline-2,5,10(1H)-triones under Green Conditions

2020 ◽  
Vol 23 (23) ◽  
pp. 2626-2634
Author(s):  
Saiedeh Kamalifar ◽  
Hamzeh Kiyani
Keyword(s):  
Reaction Medium ◽  
Meldrum's Acid ◽  
Meldrum’S Acid ◽  
One Pot ◽  
One Pot Synthesis ◽  
Substituted Benzaldehydes ◽  
High Yields ◽  
First Time ◽  
Green Conditions

: An efficient and facial one-pot synthesis of 4-aryl-3,4-dihydrobenzo[g]quinoline- 2,5,10(1H)-triones was developed for the first time. The process proceeded via the three-component cyclocondensation of 2-amino-1,4-naphthoquinone with Meldrum’s acid and substituted benzaldehydes under green conditions. The fused 3,4-dihydropyridin-2(1H)- one-ring naphthoquinones have been synthesized with good to high yields in refluxing ethanol as a green reaction medium. This protocol is simple and effective as well as does not involve the assistance of the catalyst, additive, or hazardous solvents.

Oxidation of (1-hydroxybenzyl)ferrocene and its derivatives substituted in phenyl ring with bis(triphenylsilyl) chromate

1982 ◽  
Vol 47 (12) ◽  
pp. 3375-3380 ◽  
Author(s):  
Jaroslav Holeček ◽  
Karel Handlíř ◽  
Milan Nádvorník ◽  
Milan Vlček
Keyword(s):  
Linear Dependence ◽  
Rate Constants ◽  
Oxidation Rate ◽  
Phenyl Ring ◽  
Equilibrium Constants ◽  
Aprotic Solvents ◽  
Protonation Equilibrium ◽  
Oxidation Of Alcohols ◽  
Hammett Σ Constants ◽  
Sulphuric Acid Medium

Kinetics have been studied of oxidation of (1-hydroxybenzyl)ferrocenes substituted in phenyl ring with bis(triphenylsilyl) chromate in benzene solutions as well as protonation of these alcohols in sulphuric acid medium. Logarithms of the oxidation rate constants (kobs, 20-40 °C) and those of the protonation equilibrium constants (KR+, 25 °C) show linear dependence on the Hammett σ constants, the ρ constant values being -0.86 to -0.40 and -2.50, respectively. These negative values suggest that the both processes are influenced by the same effects and confirm the mechanism proposed earlier for oxidation of alcohols with ferrocenyl substituent by action of bis(triphenylsilyl) chromate in aprotic solvents.

scholarly journals Cover Feature: Cp*Rh(III)‐Catalyzed C8 C−H Alkylation of Quinoline N ‐Oxides with Diazo Meldrum's Acid (Eur. J. Org. Chem. 3/2021)

2021 ◽  
Vol 2021 (3) ◽  
pp. 325-325
Author(s):  
Malcolm P. Huestis ◽  
Jean‐Philippe Leclerc ◽  
Robin Larouche‐Gauthier ◽  
Samuel Aubert‐Nicol ◽  
Arun Yadav ◽  
...  
Keyword(s):  
Meldrum's Acid ◽  
Meldrum’S Acid
Sign in / Sign up

Export Citation Format

Share Document