Synthesis and characterization of some new Schiff bases of 2-oxonaphtho[2,1- b ][1,4]oxazine

The literature review reveal that [1,4]-oxazine derivatives represent one of the most active classes of compounds possessing wide spectrum of biodynamic activities and use as potent therapeutic agents. In the present work, a series of Schiff base of 2-(2,3-dihydro-2-oxonaphtho[2,1-b][1,4]oxazin-1-yl)acetohydrazide, 5a-5j has been synthesized using 1-aminonaphthalen-2-ol. Various aromatic aldehyde were react with carbohydrazide 4 in the presence of acid to produce the 2-oxonaphtho[2,1-b][1,4]oxazin Schiff base derivatives with good yields. All synthesized compounds were characterized by IR, NMR and Mass spectrometry analysis.


EXPERIMENTAL
All chemicals and solvents were purchased from Spectrochem Pvt Ltd., Mumbai of AR grade and were used without further purification. Melting points were taken in open capillary method and are uncorrected. IR spectra were recorded on FTIR-8400 spectrophotometer (Shimadzu, Kyoto, Japan), using DRS probe KBr pallet. 1 H-NMR spectra of the synthesized compounds were recorded on a Bruker-Avance-II (400 MHz) DMSO-d 6 solvent.
Chemical shifts are expressed in δ ppm downfield from TMS as an internal standard. Mass spectra were determined using direct inlet probe on a GCMS-QP 2010 mass spectrometer (Shimadzu, Kyoto, Japan). Physical constants of the synthesized compounds 5a-5j are shown in Table 1.

1. Synthesis of 2-chloro-N-(2-hydroxynaphthalen-1-yl)-acetamide (1)
To the suspended solution of 1-aminonaphthalen-2-ol hydrochloride (6 mmol) in THF (10 ml); triethylamine (2 ml) and chloroacetyl chloride (6 mmol) was added under cooling condition and allowed to stir overnight at room temperature. The reaction mixture was poured onto ice-cold water and extracted with ethyl acetate. The obtained organic layer was washed with water and saturated brine, and dried over anhydrous sodium sulfate. The solvent was evaporated; titled compound was obtained as a dark brown solid. Yield: 86 %
The obtained organic layer was washed successively with 1N hydrochloric acid, water and saturated brine, and dried over anhydrous sodium sulfate. The solvent was evaporated; title compound was obtained as a dark brown solid. Yield: 78 %

3. Synthesis of ethyl 2-(2,3-dihydro-2-oxonaphtho[2,1-b][1,4]oxazin-1-y1)acetate (3)
To a solution of compound 2 (6 mmol) in 10 ml DMF, potassium carbonate (0.9 g) was added at room temperature. This was followed by the addition of Ethylbromoacetate (6 mmol) at 0-5 °C. The reaction mixture was refluxed until completion of reaction. The reaction mixture cooled to room temperature and poured onto ice-cold water followed by extraction with ethyl acetate. The combined organic layer was evaporated to get compound 3 as brown liquid, which was directly taken for hydrolysis. Crude yield 64 %

CONCLUSION
We have established facile and convenient method for the synthesis of Schiff base of 2-(2,3-dihydro-2-oxonaphtho[2,1-b] [1,4]oxazin-1-yl)acetohydrazide under a conventional reagent. All synthesized compounds were obtained in good to moderate yield. All synthesized compounds were characterized by IR, NMR and Mass spectrometry analysis and are incorporate with the structure of compounds 5a-5j.
International Letters of Chemistry, Physics and Astronomy Vol. 31 29