Microwave assisted synthesis of some isoxazoles

A pair of isoxazole derivatives A and B has been prepared by reacting 6-( 4 - fluoro phenyl ) - 3 - cyano-4-methylsulfanyl-2H-pyranon-2-one with hydroxylamine hydrochloride. A is 3-amino-6- ( 4 - fluoro phenyl ) pyrano[4,3-c]isoxazol-4-one and B is [3- ( 4 -fluoro phenyl ) isoxazol-5-yl] acetonitrile. The starting material has two positions susceptible to nucleophilic attack. The first position is at C-4 and the second at C-6. The attack at C - 4 leads to formation of A by usual ring closure. The attack at C - 6 leads to ring opening followed by decarboxylation and recyclisation to an intermediate which eliminates methanthiol to produce B.