1,3-DIPOLAR CYCLOADDITIONS TO 5-METHOXY-2(5H)-FURANONE

Various nitrile oxides and nitrones, ethyl diazoacetate and an azomethine ylide were examined in 1,3-dipolar cycloadditions to 5-methoxy-2[5H]-furanone, in particular with respect to regio- and diastereoselectivities. Isoxazoles 13-17 and isoxazolidines 21, 22 and 24 were obtained in high yields with and-facial selectivities and regioselectivities exceeding 95%. In the case of pyrazoline 26 minor amounts of syn-facial adduct are also observed, whereas lactone annulated pyrrolidines 28 are obtained as mixtures of regio-isomers.