Tetrazole ring construction

A benzofuran ring replaces one of the benzene rings of the biphenyl moiety present in many of the sartans in the rather more complex drug saprisartan (80-10). It is of note, further, that the acidic proton is provided in this case by a trifluorosulfo-namide instead of the more common tetrazole ring. Construction of the imidazole fragment begins by nitrosation of the (3-ketoester (79-1) by means of sodium nitrite in acid to afford the oxime (79-2). Reaction with acetyl chloride leads to the ester (79-3). Reaction of this last intermediate with the iminoether from propionitrile then affords the imidazole (79-4). 

Cilostazol has been used to treat intermittent claudication in individuals widi peripheral vascular disease. A similar molecule as cilostazol may have the risk of death in patients with congestive heart failure. The synthesis of cilostazol contains a 1,3-dipolar addition for the construction of the tetrazole ring, and the resulting tetrazole was coupled with 6-hydroxy-3,4-dihydroquinolin-2(l//)-one with the aide of potassium hydroxide. ... 

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