An optically active 4,4-di-substituted oxazolidine compound having the formula (I) ##STR00001## wherein R.sup.1 represents a substituted C.sub.1-C.sub.3 alkyl group, a substituted C.sub.2-C.sub.3 alkenyl group, a formyl group, a hydroxymethyl group, a group of the formula COOR, a halogenated methyl group, a phosphonium methyl group; R represents a C.sub.1-C.sub.6 alkyl group, a C.sub.2-C.sub.6 alkenyl group, a phenyl group or a benzyl group; R.sup.2 represents a C.sub.1-C.sub.6 alkyl group, a C.sub.3-C.sub.10 cycloalkyl group, or a phenyl group; R.sup.3 represents a C.sub.2-C.sub.6 alkanoyl group, a C.sub.1-C.sub.6 alkyloxycarbonyl group, a benzoyl group, a phenyloxycarbonyl group or a benzyloxycarbonyl group and R.sub.4 represents a C.sub.1-C.sub.6 alkyl group or a C.sub.2-C.sub.6 alkenyl group.