Reactions of 2‐isocyanatobenzoyl chloride and 2‐carbomethoxyphenyl isocyanate with 5‐aminotetrazole

Treatment of 2‐isocyanatobenzoyl chloride ( 4 ) with 5‐aminotetrazole (5‐AT) gave 3‐(5‐tetrazolyl)quinazoline‐2,4(1 H ,3 H )‐dione ( 1 ) directly. Treatment of 2‐carbomethoxyphenyl isocyanate ( 5 ) with 5‐AT gave 2‐[((5‐amino‐1 H ‐tetrazol‐1‐yl)carbonyl)amino]benzoic acid methyl ester ( 6 ) as a kinetic product, which was thermally isomerized to 2‐[((1 H ‐tetrazol‐5‐ylamino)carbonyl)amino]benzoic acid methyl ester ( 7 ), the thermodynamically more stable urea. Cyclization of 7 with polyphosphoric acid gave 2‐(1 H ‐tetrazol‐5‐ylamino)‐4 H ‐3,1‐benzoxazin‐4‐one ( 2 ). Urea 6 was quite labile in solution, as shown by nmr, and readily reacted with methanol to give 2‐[(methoxycarbonyl)amino]benzoic acid methyl ester ( 10 ).