PURPOSE: To obtain a compound useful as an intermediate for synthesizing drugs by a simple operation economically and in high yield without using a reagent having high toxicity, by rearranging and hydrolyzing a haloacetal in a proton solvent in the presence of a base.
CONSTITUTION: A haloacetal shown by formula I (R 1 is H or lower alkyl; R 2 is lower alkyl; X is halogen) is reacted in a proton solvent (e.g. water-methanol) in the presence of a base (e.g. NaOH) at 50°CW the reflux temperature for 1W several tens hours to give the aimed substance shown by formula II. The amount of the base used is at least ≥2 equivalents based on the haloacetal. The haloacetal shown by formula I is readily obtained by a well-known method of reacting a haloketone with a primary alcohol and an orthoformic ester.