Diastereomeric ester compound useful as an intermediate in the making of an optically active 3,4-dihydro-3,4-epoxy-2H-1-benzopyran compound

A compound of the formula (I):

• ##STR6## wherein R.sup.1 and R.sup.2 are the same or different, and each is hydrogen, C.sub.1-6 alkyl, or R.sup.1 and R.sup.2 combinedly together form C.sub.2-5 alkylene;
• R.sup.3 and R.sup.4 are the same or different, and each is hydrogen, halogen, nitro, cyano, amino, C.sub.1-6 alkyl, halo-C.sub.1-6 alkyl, C.sub.1-6 alkoxy, halo-C.sub.1-6 alkoxy, carboxy, C.sub.1-6 alkoxycarbonyl, formyl, C.sub.2-6 alkanoyl, halo-C.sub.2-6 alkanoyl, benzoyl, naphthoyl, phenyl-C.sub.2-6 alkanoyl, naphthyl-C.sub.2-6 alkanoyl, formylamino, C.sub.2-6 alkanoylamino, benzoylamino, naphthoylamino, phenyl-C.sub.2-6 alkanoylamino, naphthyl-C.sub.2-6 alkanoylamino, carbamoyl, C.sub.1-6 alkylcarbamoyl, di-C.sub.1-6 alkylcarbamoyl, C.sub.1-6 alkylthio, halo-C.sub.1-6 alkylthio, C.sub.1-6 alkylsulfinyl, halo-C.sub.1-6 alkylsulfinyl, phenylsulfinyl, naphthylsulfinyl, C.sub.1-6 alkylsulfonyl, halo-C.sub.1-6 alkylsulfonyl, phenylsulfonyl, naphthylsulfonyl, sulfamoyl, C.sub.1-6 alkylsulfamoyl, di-C.sub.1-6 alkylsulfamoyl, in which the term "phenyl", "naphthyl", "benzoyl" and "naphthoyl" include substituted phenyl, substituted naphthyl, substituted benzoyl and substituted naphthoyl by at least one substituent selected from the group consisting of halogen, hydroxy, amino, cyano, C.sub.1-6 alkyl, C.sub.1-6 alkoxy and trifluoromethyl on the ring;
• Ar is phenyl, naphthyl, thienyl, furyl, or substituted phenyl, substituted naphthyl, substituted thienyl, substituted furyl and substituted pyridyl by at least one substituent selected from the group consisting of halogen, hydroxy, nitro, C.sub.1-6 alkyl, C.sub.1-6 alkoxy and trifluoromethyl;
• Y is --(CH.sub.2).sub.q -- wherein q is integer of 2;
• X is bromine, chlorine or iodine and an optically active compound thereof.