Electrochemical Synthesis of 4-(Dihydroxyphenylthio)-2H-chromen-2-one Derivatives

Abstract

The number of natural and synthetic coumarin (2H-chromen-2-one) derivatives 1) have been reported to exert notably antimicrobial 2,3) as well as antifungal, 4,5) tuberculostatic 6) and anti-human immunodeficiency virus (HIV) 7,8) activity. Moreover, the antibiotic novobiocin belongs to the hydroxycoumarin series. The importance of these compounds have motivated many workers to synthesize a number of them, and numerous methods have been developed for their preparation.9-11) On the other hand, catechols are a promising group of compounds worthwhile for further investigation, which may lead to the discovery of selective acting, biodegradable agrochemicals having high human, animal and plant compatibility. 12,13) A literature survey reveals that, in contrast to the widely studied, coumarin derivatives, no paper has reported the synthesis of 4-(dihydroxyphenylthio)-2H-chromen-2-one derivatives. Following our experiences in electrochemical oxidation of catechols in the presence of nucleophiles, [14][15][16][17][18][19][20][21] we envisaged that synthesis of organic compounds with both structures of catechol and coumarin might cause an enhancement of pharmaceutical properties and medicinal activities. This idea prompted us to investigate the electrochemical oxidation of catechols in the presence of 4-mercaptocoumarin as the nucleophile and we have discovered an easy and one-pot electrochemical method for the synthesis of 4-(dihydroxyphenylthio)-2H-chromen-2-one derivatives (4a-d) in high yield and purity, using this environmentally friendly method with high atom economy. In order to study the feasibility of the electrochemical synthesis of 4-(dihydroxyphenylthio)-2H-chromen-2-one derivatives (4a-d) and mechanistic aspects of this conversions, electrochemical oxidation of catechols in the absence and presence of 4-mercaptocoumarin was studied using cyclic voltammetry. As well, in this work computational studies were used for quantitative answer to the question concerning the difference in electrochemical oxidation of catechol in the presence of 4-hydroxycoumarin and 4-mercaptocoumarin. Results and DiscussionElectrochemical Studies Figure 1, curve a, shows the voltammetric curve obtained for the oxidation of catechol (1 mM) in water/acetonitrile (50/50) solution containing sodium acetate (cϭ0.2 M) on a glassy carbon electrode. In the studied potential-range, a well defined voltammetric curve is obtained that has an anodic (A 1 ) and the corresponding cathodic (C 1 ) peaks. These peaks are correspond to the oxidation of catechol (1a) to o-benzoquinone (2a) and vice versa within a quasi-reversible two electron process.14-21) The oxidation of catechol (1a) in the presence of 4-mercaptocoumarin (3) as a nucleophile was studied in some details. The 4-(dihydroxyphenylthio)-2H-chromen-2-one derivatives have been synthesized by direct electrochemical oxidation of catechols in the presence of 4-mercaptocoumarin as a nucleophile in water/acetonitrile (50/50) solution, in a one-pot process, at carbon rod electrode, in an undivided...

Mechanistic study of homogeneous reactions coupled with electrochemical oxidation of catechols

“…The results revealed that the quinones derived from catechols participate in a Michael type addition reaction via an EC mechanism converted to the corresponding catechol derivatives. The electrochemical synthesis of various thiocatechol products (Table 2) has been successfully performed at a carbon rod electrode and in an undivided cell with good yields and high purity [18][19][20][21][22][23][24][25][26].…”

“…The sulfone derivatives of catechol (21) are also obtained through the Michael type addition of benzenesulfinic acids (20) to anodically generated o-benzoquinones (Scheme 5) [27][28][29][30][31][32][33].…”

Electrochemical Oxidation of Catechols in the Presence of Phenyl-Meldrum's Acid. Synthesis and Kinetic Evaluation

“…1, curve a). [2][3][4][5][6][7][8][9][10][11] The electrooxidation of catechol (1a) in the presence of phenyl-Meldrum's acid (3) was studied in some detail. Fig.…”

“…Many flavonoids and catechol derivatives turned out to be as antimicrobial agents. 1) In this connection, in order to synthesis catechol derivatives, we studied the electrochemical oxidation of benzenediols in the presence of CH acid nucleophiles, [2][3][4] SH acid nucleophiles, [5][6][7][8][9] nitrite ion 10) and triphenylphosphine. 11) Also, it is demonstrated that, in comparison with simple catechols, the "highly oxygenated compounds with catechol ring" exhibit interesting biological activities.…”

A facile method for the synthesis of thiocoumestan derivatives

“…The synthesis of 4-phenylthio-2H-chromen-2-ones has been reported previously by us and several groups using different approaches [32][33][34][35][36]. However, to the best of our knowledge, no reaction of o-benzoquinone 2d with 4-mercaptocoumarin (3) has been reported and this method described an efficient and one-pot method for the synthesis of 4-(4,5-dihydroxy-2-methylphenylthio)-2H-chromen-2-one (4d).…”