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Table 2 Isolated yields for the microwave-assisted condensation of benzaldehydes 6 or naphthaldehydes 8 with thiosemicarbazide 5 and comparison with traditional methods

From: Microwave-assisted synthesis and antioxidant properties of hydrazinyl thiazolyl coumarin derivatives

Entry

Compound

R1

R2

R3

R4

Yield% under microwave irradiation†

Yield% using traditional conditions‡

1

7a

OH

H

H

H

70

69

2

7b

H

OH

H

H

82

66

3

7c

H

H

OH

H

71

71

4

7d

OH

H

OH

H

n/a

76

5

7e

OH

H

H

Br

78

64

6

7f

OH

OMe

H

H

72

69

7

9a

H

-

-

-

92

67

8

9b

OH

-

-

-

72

62

  1. † Isolated yield after microwave dielectric heating in EtOH at 120°C for 10 min (hold time) in a sealed tube using a CEM Discover single-mode microwave synthesizer by moderation of the initial magnetron power (20–150 W), followed by purification by recrystallization (EtOH). ‡ Isolated yield after reaction by traditional conductive heating at reflux in MeOH in the presence of AcOH for 1–4 h and purification by recrystallization (EtOH or EtOH–CHCl3) (see reference 20 for details). n/a Experiment not investigated.