Synthesis and antioxidant properties of some new thiazolyl coumarin derivatives

Figures & data

Scheme 1. Synthetic protocol of 3-acetyl-4-hydroxycoumarin 1.

Scheme 2. Protocol synthesis of thiazolyl coumarins derivative 2a.

Table 1. Synthesis of thiazolyl coumarins derivative 2a in the presence of different solvents.

Entry	Solvent	Temperature (°C)	Yield^a,b (%)
1	DMC	90	96
2	DEC	130	85
4	EtOH	78	80
5	CH3CN	82	65
6	THF	66	70
7	CH2Cl2	40	72
8	Toluene	110	75

Note: DMC: dimethyl carbonate and DEC: diethyl carbonate.

^aAll reactions were carried-out with 3-acetyl-4-hydroxycoumarin (5 mmol), benzaldehyde (5 mmol) and thiourea (5 mmol) and ammonium acetate (5 mmol).

^bYield of the isolated product.

Table 2. Effect of catalyst amount on the condensation of 3-acetyl-4-hydroxycoumarin and benzaldehyde with thiourea in DMC^a.

Entry	Catalyst	mmol (%)	Yield (%)^b
1	NH4OAc	5	96
2	NH4OAc	10	85
3	NH4OAc	15	75
4	NH4OAc	20	70
5	No catalyst	-	10

^aAll reactions were carried with 3-acetyl-4-hydroxycoumarin (5 mmol), benzaldehyde (5mmol), thiourea (5mmol) and ammonium acetate (5 mmol).

^bYield of the isolated product.

Table 3. Optimization of the time reaction in DMC.

Entry	Time (h)	Yield^a,b (%)
1	1 h 30	85
2	2 h	80
4	2 h 30	78
5	4 h	96
6	5 h	70

^aAll reactions were carried with 3-acetyl-4-hydroxycoumarin (5 mmol), benzaldehyde (5mmol), thiourea (5mmol) and ammonium acetate (5 mmol).

bYield of the isolated product.

Scheme 3. Synthetic protocol of thiazolyl coumarins derivatives 2a-f.

Table 4. Synthesis of thiazolyl coumarins derivatives 2a-f.

R	Product 2	Yield (%)
H	2a	96
p-NO2	2b	78
m-hydroxy	2c	85
p-OCH3	2d	82
p-CH3	2e	85
p-benzyloxy	2f	88

Notes: All reactions were carried out with benzaldehyde derivatives (5 mmol), 3-acetyl-4-hydroxycouamrin (5 mmol), thiourea (5 mmol), ammonium acetate (5 mmol) and solvent DMC (15 ml); (t = 4h) under reflux condition.

Scheme 4. A plausible mechanism for the synthesis of thiazolyl coumarins derivatives (2a-f).

Scheme 5. Synthesis of thiazolyl coumarins derivatives (2a-f) by the second path.

Figure 1. Scavenging activity of thiazolyl coumarins derivatives 2 on DPPH radicals.