Indian Joual of Chemistry Vol. 40B, September 21 , pp 837-838 Note Microwave assisted synthesis of 1,8- naphthyridines K Mogilaiah*, N Vasudeva Reddy & R Babu Rao Department of Chemistry, Kakatiya University, Warangal 5& 009, India Received 30 March 2000; accepted (ravised) JO August 2000 A highly efficient and practical methodology for the synthesis of 2-aryl -1 ,8-naphthyridines 3 is descrid starting from 2-aminonicotinaldehyde 1 and various acetophenones under microwave conditions. Novel approaches to ecofriendly chemistry demands usage of domestic microwave oven for the synthesis of heterocycles, a practically convenient, safe and rapid methodology 1. 1 ,8-Naphthyridine derivatives are reported to possess interesting pharmacological properties 5 . 7 • In view of this, we herein report a very clean, rapid and high yielding method for the preparation of 1,8-naphthyridines using microwave irradiation under solvent free conditions. Condensation of 2-aminonicotinaldehyde 1 with various acetophenones 2 in the presence of KOH without any solvent under microwave irradiation fuished 2-aryl -l,8-naphthyridines 3 in excel lent yields (Scheme I). It is noteworthy that the reaction is completed within 5 min and in the absence of a solvent. This is much superior method compared to the literature one, 8 wherein the above reactants had to be refluxed for 3 hr in ethanol and 20% KOH to give moderate yields of the products. All reactions were performed in a commercial microwave oven operating at 2450 MHz frequency. In a typical case, equimolar quantities of 2- aminonicotinaldehyde 1, acetophenone and KOH were mixed together without solvent in a 100 mL conical flask capped with a glass funnel and placed in microwave oven and irradiated for 3 min. The reaction mixture was allowed to attain room temperature, treated with cold water and filtered off. After usual work-up 2-phenyl- l ,8-naphthyridines 3a was obtained in 90% yield. The reaction is of general applicability and the different 1 ,8-naphthyridines �CHO �. + N NH2 KOH • b d 2 , p-CH 3C.H. p-CH3OC.H . p-CIC.H. p-B.H. o-HOC.H. p-HO C.H. h k m n Scheme I .� �R � 3 m-N02C.H. p-N02C.H. p-CoHsC.H. 2-CIOH, . 2-C,H.N 3,CsH.N 4-C,H.N synthesized are given in Table I. The compounds were characterized and compared with authentic samples (TLC, m.p ., JR, I H NMR and MS). The effect is not purely thermal, which is supported by the fact that when same reaction was carried out using the conventional heating mode (oi l-bath) at same final temperature and reaction time as measured in the microwave experiment, traces of products were isolated aſter the complete work-up. Reactions were faster under microwave i r radiation than under conventional heating mode at the same temperature. In conclusion, the present methodology provides a highly efficient and practical synthesis of tit le compounds with following advantages : Significant shortening of the reaction time, high yields and solvent free conditions. This is the first report on a rapid synthesis of the 1 ,8-naphthyridines where microwave technique has been utilized. Experimentral Section Melting points were taken on Cintex melting point apparatus and are uncorrected. IR spectra were recorded on a Perkin-Elmer 337 spectrophotometer using KBr discs and I H NMR spectra on a Varian Gemini 200 MHz spectrometer using Me4Si as inteal standard. Mass spectra were SC .nned on a Jeol JMS D-3 spectrometer. The purity of the compounds was checked by TLC.