NEW MATERIAL: A compd. of formula I (wherein R is H, an alkyl, an alkanoyl, an alkoxyalkyl, a lower alkylaminocarbonyl, etc.; R0, R1 and R2 are each H, a lower alkyl, a lower alkenyl, or a lower cycloalkyl; X1 and X2 are each a tert. alkyl, trimethylsilyl or CF3; and n is 1-3) and its nontoxic pharmaceutically allowable salts.

EXAMPLE: 4-(3,5-Di-tert-butyl-4-hydroxybenzylidene)-2-methyl-3-isoxazolidinone.

USE: Curing agents for inflammation, pain and pyrexia.

PROCESS: Bezaldehyde of formula II and a hetero-α-halogen-carbonyl of formula III are condensed in the presence of zinc according to Reformatskij reaction and then, hydroxymethylene intermediate product of formula IV is dehydrated by using P2O5, etc., to obtain the compd. of the formula I.