Claisen-Schmidt condensation of 2-(4-acetylphenylamino)-3-(3-chlorophenyl)-1,8-naphthyridine 3 with various aromatic aldehydes in solvent-free conditions under microwave irradiation using slid NaOH afforded 2-(4-cinnamoylphenylamino)-3-(3-chlorophenyl)-1,8-naphthyridines 4. The compounds were characterized by elemental analysis, IR, H-1 NMR and mass spectral data. Compounds 4 have been tested for their antibacterial activity.

Diacylhydrazines are very important synthons for the synthesis of bioactive compounds such as oxadiazoles and thiadiazoles. Amongst different methods of preparing diacylhydrazines, much attention have been paid to oxidation of acid hydrazides. Many oxidizing agents such as lead tetracetate 1 , halogens 2 , selenium oxidants 3 and iodobenzene diacetate 4 have been used for oxidative dimerization of acid hydrazides. However, some of these methods suffer from disadvantages such as long reaction times, the lower yields of the products, the requirement of severe conditions and the use of the strong and expensive oxidants. Therefore, development and introduction of convenient, milder and efficient method for the oxidation of acid hydrazides to the corresponding diacylhydrazines is of practical importance and is still in demand. Solid state organic synthesis is an active area of research. Compared to traditional methods, many organic reactions occur more efficiently in the solid state than in solution and in some cases even more selectively. Furthermore, the solid state reaction has many advantages: low costs and simplicity in process and handling 5-8 . In view of these facts, and in continuation of our interest on solid state organic transformations 9-12 , we present herein a rapid and efficient method for the transformation of acid hydrazides to N,N′-diacylhydrazines using Hg(OAc)2 in the solid state at RT. Treatment of acid hydrazides 1 with one equivalent of Hg(OAc)2 in the solid state at room temperature furnished the corresponding N,N′-diacylhydrazines 2 in good yields (Scheme I). The reaction is fairly general, very facile, and efficient and is devoid of any byproducts. Furthermore, it is to be noted that highly pure products were obtained using this simple procedure and in most cases no further purification was needed. The experimental procedure is very simple. In a typical case, an equimolar mixture of benzhydrazide 1 (Ar = C6H5) and Hg(OAc)2 was thoroughly mixed in 25 mL conical flask, pulverized by rubbing with spatula against walls of the flask for 3.0 min at room temperature. Completion of the reaction was marked by the change of state from solid to semisolid. The reaction afforded N,N'-dibenzoylhydrazine 2 (Ar = C6H5) in 80% yield. The reaction is of general applicability and the various N,N′diacylhydrazines 2 synthesized are given in Table I. Alternatively, when solid reaction-mixture was heated on water bath slightly, reaction was completed in less than one minute. Further, when the reaction was carried out in dichloromethane with stirring for the same time as above (3.0 min) the product was obtained only in 25% yield. A plausible mechanism for the transformation of 1 to 2 is outlined in Scheme II. The intermediacy of acyldiimide 4 in the oxidative dimerization of acid hydrazides has previously been suggested by others 3,19,20 . To the best of the knowledge this is the first report on rapid transformation of acid hydrazides to N,N′diacylhydrazines using Hg(OAc)2 under solid state grinding conditions at RT. In conclusion, the present methodology provides a highly efficient and practical conversion of acid hydrazides to N,N′-diacylhydrazines with following advantages: significant shortening of the reaction time, good yields, high purity, inexpensive oxidant and solvent-free conditions.

A simple and efficient method for the synthesis of 6-aryl-9-(p-fluorophenyl)-1,2,4-triazolo [4,3-a] [1,8] naphthyridines 4 is achieved by the oxidation of p-fluorobenzaldehyde 3-aryl-1,8-naphthyridin-2-ylhydrazones 3 with chloramine-T in ethanol under microwave irradiation. The products are obtained in good yields and in a state of high purity. The structures of compounds 3 and 4 were characterized by elemental analyses, IR, (1)H NMR and mass spectral data.

Alumina-supported iodobenzene diacetate [PhI(OAc)(2)-Al2O3] is a highly efficient reagent for the oxidative cyclization of [o-(1,8-naphthyridin-2-yl)phenoxy]acetic acid arylidene hydrazides 4 to 5-aryl-2-[o-(1,8-naphthyridin-2-yl)phenoxymethyl]-1,3,4-oxadiazoles 5 in solvent-free conditions under microwave irradiation. The products are obtained in good yields and in a state of high purity.

A convenient, rapid and clean procedure for the synthesis of 2-(3-aryl-1,8-naphthyridin-2-yl)-1,2,3,4-tetrahydro-5,6,7,8-tetrachlorophthalazine-1,4-diones 3 by the reaction of 3-aryl-2-hydrazino-1,8-naphthyridines 1 with tetrachlorophthalic anhydride 2 in the presence of catalytic amount of DMF under microwave irradiation is described. The products are obtained in excellent yields and in a state of high purity.

A straightforward and highly efficient procedure has been described for the synthesis of 6-aryl-12H-pyrido[2',3':4,5]-pyrimido[1,2-a)[1,8]naphthyridin-12-ones 3 by the reaction of 3-aryl-2-chloro-1,8-naphthyridines 1 with 2-aminonicotinic acid 2 in glacial acetic acid under microwave irradiation. The products are obtained in very good yields and in a state of high purity The structural assignments of compounds 3 were based on their elemental analyses and spectral (IR and H-1 NMR) data.