Ultrasound-enhanced one-pot synthesis of 3-(Het)arylmethyl-4-hydroxycoumarins in water

Abstract

3-(Aryl)methyl-4-hydroxycoumarins were produced in good to excellent yields by reaction between 4-hydroxycoumarin and (hetero)aromatic aldehydes in the presence of Hantzsch 1,4-dihydropyridine (HEH) which works as an hydride donor (i.e., in a sequential Knoevenagel-reductive Michael addition). The sonochemical-assisted procedure (method B) provides an improved and accelerated conversion when compared to conventional silent reactions (method A). Experiments carried out according to method B showed that the reaction could be more efficiently run in the absence of organic solvents, at 30-40°C in open vessel, without the need of an excess HEH and with simplified work-up and separation procedures.

Green synthesis of quinoxaline derivatives usingp-dodecylbenzensulfonic acid as a surfactant-type Bronsted acid catalyst in water

“…DBSA works well for dehydration reactions such as the esterification and etherification in water (22), synthesis of bis(indol-3-yl)alkanes (23), xanthenes (24,25), 3-arylmethyl-4-hydroxycoumarins (26), selective a-aminoallylation (27), as well as in polymerization reactions (28Á30). Herein, we wish to report a green and efficient method for the synthesis of quinoxaline derivatives in good to excellent yields by the condensation of 1,2-diamines with 1,2-dicarbonyl compounds catalyzed by DBSA.…”

Use of Ultrasound in the Synthesis of Heterocycles of Medicinal Interest

“…These compounds are routinely used in the treatment of a variety of cardiovascular disorders such as hypertension, cardiac arrhythmias, or angina. Palmisano et al [103] worked with ultrasound at 60 W power and 19.6 kHz, for 1.5 h, to get a wide range of (het)-3-arylmethyl-4-hydroxycoumarins (134) through a tandem Michael Knoevenagel-reductive reaction (Scheme 34). The reaction was proposed to proceed via utilization of β-ketosulfone as a main synthon.…”

Green Chemistry – Aspects for the Knoevenagel Reaction

“…Figure 22 illustrates reactions between benzaldehyde (9) and coumarin (71) that can also be conducted in water under ultrasound irradiation at a temperature of 40 0 C for 90 minutes, forming product (70) in yields of 88.0% (Method B) (Palmisano et al, 2011). In the absence of ultrasound irradiation, formation of product (70) occurs in yields of 62.0% under anhydric conditions (Method A) (Palmisano et al, 2011). …”