ORIENTAL

Synthesis of oxazolonone, benzoxazolononeby using amino hydroxy compound, alkyl haloformate, trialkylamine and DMF as solvents. Herein used simple carbonylation agent such as alkylhaloformate instead of phosgene and Triphosgene. Developed novel and simple synthesis method.


INTRODUCTION
The development of heterocycles compound like oxazolonone, benzoxazolononeas frame, containing a high degree of variety has become a number one focus in medicine discovery. Various modifications on the ring by addition of various substituents suggestionnew products with advanced natural biographies. Considering strategic medical importance of oxazolonone, benzoxazolonone, developed easy and possible novel synthesis technique.
B e n z i m i d a zo l o n e s y n t h e s i ze d by carbonylation of 1,2-diamino benzene using a) urea and DMF [13][14] , b) carbon dioxide in water 15 27 . From amides by iodosylbenzene-induced Hofmann rearrangement 28 . Lanthanide-catalysed cyclocarbonylation and cyclothiocarbonylation 29 .
Main drawback of above all route of synthesis is generation of toxic reaction waste and critical handling of phosgene and triphosgene. In present invention, we developed simple commercially viable, non-phosgene, synthetic method.

EXPERIMENTAL
Solvents and key raw materials used for this experimentation, bought from commercial sources, and used as such. Melting points analysed on Electro-thermal IA 9100 apparatus (Shimadzu), 1 H NMR spectra analysed on a Bruker (400 MHz) spectrometer in DMSO-d 6 . The chemical shifts as ppm against tetramethylsilane (TMS) as internal reference. Duringreaction, the formation of compounds, checked by TLC on silica gel plates of 0.5mm thickness and checked location of spots by iodineand UV light.

Common procedure for preparation of compound (3a-e)
Compound 1a-e (1eq), compound-2 (1.05eq) and DMF (6.38V) taken in round bottom flask. Added Trialkylamine (1.50eq) in 1 hours. Heated reaction mass at 75-80°C, 4 hours. Heated the reaction mass at 105 to 110°C over a period of 10-15 hours. Distilled out DMF at 70 to 75°C using vacuum. Added water (8V) and distilled out traces of DMF. Cooled the reaction mass at 0 to 5°C and filtered. Wet cake dried at 55 to 60°C under vacuum. Obtained compound 3a-e (Scheme 1).

RESULTS AND DISCUSSION
Carbonylation method is most efficient for synthesis of oxazolopyridine and benzoxazolones. The major advantage of this method is nonphosgene route of synthesis. Carbonylating agent is easily available and can be manage easily on commercial scale. Trialkylamine can be easily recover and recycle in the process which reduces production cost. Phosgene is very toxic and required special storage facility where as alkyl halo formate storage is not complicated as compared to phosgene and triphosgene.  Compound 1a-e treated with compound 2 and trialkylamine in DMF as a solvent. (Scheme 1), as per General procedure for preparation of compound (3a-e) and product 3a-e yield summarized in (Table 1).

Scheme 1 Standard model reaction
Screening of different solvents such as DMF, Methanol, Acetone, DCM, and Toluene, for synthesis of 3a. Reaction done as per general procedure for preparation of compound (3a-e). Due to reaction temperature condition lower boiling solvents are not suitable. Toluene and DMF used as a mixture by selecting different ratio, noticed in 100% toluene conversion is zero. We studied increasing DMF composition observed increasing yield of reaction and in 100% DMF obtained best yield. Commercial point of view single solvent is good for cost effective process. We found that DMF is best solvent for reaction as reactants and intermediate having good solubility for effective interaction. We observed that desired product 3a formed with in 20 h, with 91% yield. Yield of 3a formation mentioned in (Table 2). After screening of various carbonylation agent such as alkylhaloformate as per General procedure for preparation of compound (3a-e).we noticed that ethyl and methyl chloroformate gives 91% yield of compound 3a. Yield of compound 3a summarized in (Table 3).  After screening of various trialkylamine as per general procedure for preparation of compound (3a-e). we noticed that triethylamine and N,N-diisopropyl ethylamine gives 91% yield of compound 3a. Yield of compound 3a summarized in (Table 4).

CONCLUSION
We have developed non phosgene, and commercially viable synthetic method for synthesis of oxazolonone, benzoxazolonone. Important advantage of this method is clean reaction profile, high yield, simple carbonylating agent. Acid scavenger can be recover and recycle in the process.

ACKNOWLEDGEMENT
Authors thankful to Principal, Vivekanand Arts & S.D. Commerce and Science College, Aurangabad (MS)-431001 for his encouragement and support.