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A facile and efficient synthesis of substituted 2-oxo-2H-chromen-7-yl phenylcarbamates fromdifferently substituted 7-hydroxycoumarin

Preet Anand, Baldev Singh

The study was aimed to synthesize substituted 2-oxo-2H-chromen-7-yl phenylcarbamates fromdifferently substituted 7-hydroxycoumarin by three different methods. In Ist method, substituted 2-oxo-2H-chromen-7- ylphenylcarbamate derivatives were synthesised in two steps by reacting benzoyl chloride with differently substituted 7-hydroxycoumarin in the presence of NaOH followed by reaction of an intermediate with sodium azide. In 2nd and 3rd methods, substituted 2-oxo-2H-chromen-7- ylphenylcarbamates were synthesized in a single step by reacting differently substituted 7-hydroxycoumarin with phenyl isocyanate or phenylcarbamic chloride, respectively. Due to lower yields (30-40%for Ist and 50-60% for 3rd method), longer reaction time (8-10 hours for Ist and 1 hour for 3rd method), hygroscopic and lacrimating reagents (benzoyl chloride and phenyl carbamic chloride), the Ist and 3rd methods were inconvenient as compared to 2nd method with higher yield (85-95%) and shorter reaction duration (15 min). Therefore, one pot synthesis of substituted 2- oxo-2H-chromen-7-ylphenylcarbamates may be conveniently achieved by reacting phenylisocyanate with differently substituted 7-hydroxycoumarin in the presence of triethylamine and petroleum ether.