Indian Journal of Chemistry Vol. 45B, January 2006, pp. 267-271 Novel approach for the rapid and efficient synthesis of heterocyclic Schiff bases and azetidinones under microwave irradiation Bhanvesh Naik & K R Desai* Department of Chemistry, Veer Narmad South Gujarat University, Surat 395 007, India E-mail: Bhanveshnaik@yahoo.co.in Received 25 October 2004; accepted (revised) 28 March 2005 A series of compounds, viz. 3′′-chloro-4′′-(substituted phenyl)-1′′-[4-(coumarin-3-yl)thiazol-2-yl]-2′′-azetidinones 4a-j have been prepared by the reaction of 2-N-(substituted benzylidene)imino-4-(coumarin-3-yl)thiazoles 3a-j with chloroacetyl chloride in the presence of triethylamine. The Schiff bases 3a-j have been prepared by the condensation of 2-amino-4- (coumarin-3-yl)thiazole 1 with different aldehydes 2. Both the reactions are carried out by conventional and microwave methods. The products are screened for their antibacterial activity against Staphylococcus aureus, Bacillus subtillis, Escherichia coli and Salmonella typhi. IPC: Int.Cl. 7 C 07 D Keywords: Schiff base, azetidinone, microwave, antibacterial activity A survey of literature reveals that thiazolocoumarins possess a broad spectrum of biological importance. Thiazolocoumarin derivatives are well known biologically active compounds. Coumarin derivatives possess antibacterial 1 , anticoagulant 2 and anti-allergic 3 activities. Schiff base has good antimicrobial, fungicidal 4 and pharmacological applications 5 and it can be prepared by the acid catalyzed reaction of amines and ketones or aldehydes. 2-Azetidinone deri- vatives have been reported to possess anti-inflammatory, antidegenerative, fungicidal 6 and antibiotic 7 activity. The microwave irradiation is used for carrying out chemical transformations which are pollution free and eco-friendly 8,9 . Herein we wish to present a detailed research work on the synthesis of Schiff bases and azetidinones using N,N-dimethylformamide as a reaction mediator, which absorbs microwave energy efficiently through dipole rotation since it can retain water formed in the reaction thus avoiding the need for a water separator 10 . Commercial microwave oven is used as a convenient source of heat in the laboratory. The microwave assisted organic reactions occur more rapidly, safely and with higher chemical yields 11,12 . These features render the microwave method superior to the conventional one. The starting compound namely, the substituted 2- amino-4-(coumarin-3-yl)thiazole 1 was synthesized from the reaction of 3-bromoacetylcoumarin with thiourea 13 . The condensation of 1 with substituted aldehydes 2a-j was carried out by both conventional and microwave methods to get 2-N-(substituted benzylidene)imino-4-(coumarin-3-yl)thiazoles 3a-j. In conventional method, the reaction was carried out in methanol and it took 5 to 6 hr. But it took only 2 to 3 min under microwave irradiation 14 . Reaction of the Schiff bases 3a-j with chloroacetyl chloride in the presence of triethylamine was carried out by conventional method in benzene as a solvent to yield 3′′-chloro-4′′-(substituted phenyl)-1′′-[4-(coumarin- 3-yl)thiazol-2-yl]-2′′-azetidinones 4a-j. It took 15-16 hr, while under microwave irradiation using DMF as a solvent the reaction was completed in 3 to 4 min (Scheme I). A comparative study in terms of yield and reaction period is shown in Table I and Table II. Experimental Section All the melting points were determined on a PMP-DM scientific melting point apparatus and are uncorrected. The purity of compounds was checked by TLC on silica gel ‘G’ coated glass plates. IR spectra were recorded with KBr on a Shimatzu FT-IR 8300 spectrophotometer; 1 H NMR spectra on a Brucker DRX-300 in CDCl 3 at 200 MHz using TMS as an internal standard. Microwave assisted reactions were carried out in a “QPro-M Modified Microwave System” made in Canada.