PURPOSE: To obtain a butyrolactone compound having a cdc2 phosphorylation- inhibiting ability and a cell multiplication-inhibiting ability, and useful as an antitumor agent or an immunosuppressive agent by subjecting a specific compound to a rearrangement in the presence of a Lewis acid catalyst.

CONSTITUTION: A compound of formula I (R is 1-4C alkyl) is subjected to a rearrangement in the presence of (B) a Lewis acid catalyst preferably comprising boron trifluoride.ethyl ether complex in an inactive solvent such as chloroform usually at -100 to 50°C (preferably -78°C) ordinarily for 5min to 3hr (preferably 30 min to 1.5 hr) to obtain a compound of formula II. The amount of the component B is usually 0.1-3 equivalents (preferably 1-2 equivalents) based on the component A. The compound includes α-oxo-β-(p-hydroxyphenyl)-γ-[p-hydroxy- m-(3-methyl-2-buten-l-yl)benzyl]-γ-methoxycarbonyl-γ-butyrolactone.