PURPOSE: To obtain the titled compd. having activities of anti-entozoic property, anti-exozoic property, fungicidal property, pesticidal property, nematocidal property and tickicidal property, and useful to exterminate pests and as an intermediate of a pesticide by oxidizing a specified compd. in the presence of a phase transfer catalyst.

CONSTITUTION: A compd. expressed by formula I (wherein R1 is methyl, ethyl or isopropyl; R2 is H, methyl or acetyl; R3 is H, or OR2 and R3 with C atom attached form >C=O) is oxidized in a mineral acid or an ester solvent by using an oxidizing agent such as sodium bichromate and pyridinium dichromate. Then the oxidized compd. is subjected deacetylation if necessary to obtain the objective compd. expressed by formula II.