Microwave-assisted synthesis of 3,1-benzoxazin-2-ones from 3-hydroxyoxindoles

A general protocol for the synthesis of 3,1-benzoxazin-2-ones 18 from 3-hydroxyoxindoles 16 in a two steps sequence through phenylsuccinates or phenylpropionates 17 is described. Best reaction conditions for ring opening of 16 to succinates or propionates17 were achieved using alcohol/silica gel, while cyclization of 17 to benzoxazinones 18 was easily done with HCl/alcohol. It was also found that 17 and 18 can be transesterified using HCl/alcohol. Most transformations were carried out by traditional heating and by microwave (MW) irradiation to accelerate reaction rates.