PURPOSE: To provide a new optically active piperidinediol containing a difluoromethyl group and useful as an anti-HIV active compound.

CONSTITUTION: 2-Difluoromethylpiperidine-3,4-diol represented by formula I. The compound of formula I can be obtained through a new intermediate, a new N-substituted 2-difluoromethylpiperidine-3,4-diol of formula VI synthesized from a new N-substituted 2-difluoromethyl-3-hydroxy-2,3-dihydro-4-pyridone of formula V prepared by reacting a dihydropyridone of formula II (R is a 1 to 20C alkyl, a 6 to 20C aryl or a 7 to 20C arylalkyl) with sodium bis(trimethylsilyl) amide of formula III and subsequently reacting 2- sulfonyloxazolidine of formula IV therewith.