Sergio Thea

Tele substitution in the naphthalene series. Reaction of 1,4-dimethyl-2,3-dinitronaphthalene with secondary aliphatic amines☆

1,4-Dimethyl-2,3-dinitro-naphthalin (I) reagiert mit den beiden sekundaren Aminen (II) zu den Substitutionsprodukten (III).

Tandem reduction/intramolecular hydroxyalkylation of (3-hydroxyphenyl)alkanoates : a new regioselective approach to 1,8-dihydroxytetralins

Abstract 4-(3-hydroxyphenyl)-butanoates 4 , on treatment with DIBALH, followed by hydrolytic work-up, undergo a novel completely regioselective intramolecular hydroxyalkylation reaction to give 1,8-dihydroxytetralins. The yield of the reaction depends heavily on the structure of starting material, best results being achieved with 3,3-disubstituted butanoates.

Elimination–addition mechanisms of acyl-group transfer reactions: a novel E1cB mechanism in the hydrolysis of 2,4-dinitrophenyl 4-hydroxybenzoate

Evidence is offered for the intermediacy of an unprecedented para-oxoketen intermediate in a dissociative mechanism for the hydrolysis of the title ester.

Carbonyl-forming elimination reactions. A kinetic study of the decomposition of β-nitroalcohols in water

Abstract β-Nitroalcohols 1 a–g undergo, in aqueous buffered solution, a specific base catalyzed carbonyl-forming elimination. The transition state for the rate-limiting CC bond breakage step has been estimated to be rather reactant-like.

Reaction of 2-nitrothiophen with secondary aliphatic amines

Secondary aliphatic amines react with 2-nitrothiophen in ethanol at room temperature to yield bis-(4-dialkylamino-1-nitrobuta-1,3-dienyl) disulphides. The disulphide is shown to be generated via the preliminary formation of the corresponding thiol. A mechanism involving nucleophilic attack by the amine at the 5 position of the nitroactivated thiophen ring, and proton tranfer to yield a sulphonium-type intermediate followed by ring-opening, is proposed.

General acid inhibition and the absence of deuterium isotope exchange in base catalysed hydrolysis of 2,4-dinitrophenyl arylmethanesulphonate esters in aqueous solution

The hydrolysis of 2,4-dinitrophenyl arylmethanesulphonates in aqueous buffers exhibits general base catalysis at low buffer concentration. The rate constant–buffer concentration plots become non-linear at high concentrations and this is interpreted as due to a change in rate-limiting step from proton transfer to the breakdown of the sulphene–2,4-dinitrophenolate ion encounter complex. Experiments with added solutes and kinetic arguments indicate that the curvature in the buffer concentration plots is not due to specific solute effects. The absence of deuterium exchange at high buffer concentration is consistent with an internal return mechanism which is more efficient than exchange processes; a water molecule is proposed to act as a relay for the transfer of proton from carbon acid to base.

Elimination–addition mechanisms of acyl group transfer: evidence for rate-limiting breakdown of a sulphene-2,4-dinitrophenoxide ion encounter complex in the base-catalysed hydrolysis of 2,4-dinitrophenyl arylmethanesulphonate esters

The base-catalysed hydrolysis of 2,4-dinitrophenyl arylmethanesulphonate esters via an E1cBi mechanism undergoes a change in rate limiting step in pyridine buffers of high concentration from proton transfer to breakdown of a sulphene-2,4-dinitrophenoxide ion encounter complex.

Mechanism in sulphonyl group transfer: effective charge in ground-, transition-, and product-states during base-catalysed hydrolysis of aryl sulphonate esters possessing associative (AE) and dissociative (EA) mechanisms

Substituent effects on rate and equilibrium constants for transfer of sulphonyl species to phenols lead to measures of the change in effective charge on participating atoms in the transition-state of the rate-limiting step; results are obtained for both dissociative and associative sulphonyl group transfer mechanisms.

Neighbouring carboxylate group participation in ester aminolysis in non-hydroxylic solvents. The n-butylaminolysis of aspirin in acetonitrile

In acetonitrile the carboxylate group of aspirin anion has been found to assist the n-butylaminolysis of the neighbouring ester function with a mechanism changing from nucleophilic to concomitant nucleophilic and probably general base catalysis as the amine concentration is increased.