Chemical and spectroscopic properties of the 3-hydroxythiophene [thiophen-3(2H)-one] system

Abstract

3-Hydroxythiophene 1 spontaneously dimerises to 4,5-dihydro-5-(3-hydroxythien-2-yl)thiophen-3(2H)-one 14. 3-Hydroxythiophenes 1E and 4-10E exist in solvent-dependent equilibrium with their thiophen-3(2H)-one 1K and 4-10K tautomers; the amount of hydroxy tautomer is greater than in the case of the corresponding 3-hydroxypyrroles. 3-Hydroxythiophenes are much less reactive to electrophiles than corresponding 3-hydroxypyrroles, but the 5-methylsulfanyl derivative 10 reacts at the 2-position with methoxymethylene Meldrum's acid and undergoes Vilsmeier formylation. The enolates derived from 3-hydroxythiophenes by treatment with base can be O-alkylated and O-acylated with high regioselectivity. 2,2-Disubstituted thiophen-3(2H)ones undergo equilibrium conjugate addition with nucleophiles, but the resulting adducts could not be isolated.

Possibilities and Constraints of the Electrochemical Treatment of Thiophene on Low and High Oxidation Power Electrodes

“…Moreover, they can behave as acylating agents owing to their vulnerable nature to ring-opening by a nucleophile attack . Tox as a tautomer of 3-hydroxythiophene can be prepared by hydroxylation of thiophene with acid-catalyzed peracid oxidation, and these two tautomers tend to dimerize spontaneously at room temperature over a few days . Tox is an intermediate during the bioactivation pathway of antiplatelet drugs .…”

Bromoarylation of Methyl 2-Chloroacrylate under Meerwein Conditions for the Synthesis of Substituted 3-Hydroxythiophenes

“…Suitable electron-withdrawing substituents at the -position of the thiophene ring shift the equilibrium toward the enol tautomer. 37 According to the 1 H NMR spectra, thiophenes 5 are enols when DMSO-d 6 is used as solvent.…”

NMR Spectroscopic Study of Tautomerism in Solution and in the Solid State

“…The keto-enol tautomeric equilibrium of 3-hydroxythiophenes 50(OH) [thiophene-3(2H)-ones 50(=O)] was systematically studied [91]. 1 H and 13 C NMR spectra were analyzed completely (e.g., 50(OH): δ(C-2) = 98.0 ppm, δ(C-3) = 155.1 ppm; 50(=O): δ(C-2) = 36.6 ppm, δ(C-3) = 203.4 ppm) and the equilibria determined.…”

“…1 H and 13 C NMR spectra were analyzed completely (e.g., 50(OH): δ(C-2) = 98.0 ppm, δ(C-3) = 155.1 ppm; 50(=O): δ(C-2) = 36.6 ppm, δ(C-3) = 203.4 ppm) and the equilibria determined. The amount of keto tautomer is greatest in nonpolar solvents [91]. Using the same methodology, the tautomeric equilibrium of the thione-thiol forms of 1,3-thiazolidine-2-thione was examined [92].…”