Waste 3-acetyl-5,8-dimetoxy-3-hydroxy-3,4-dihydro-2H-naphthalene-1-spiro-2'-1'-3'-dithiolane 4, a 7:3 mixture of (R) and (S) enantiomers on boiling with ethyl acetate afforded hydroxyketone (R)-4 with high enantiomeric purity (ca. 96%). A two-step inversion of the stereogenic center in the latter gave hydroxyketone (S)-4 in 40% yield. The overall yield of (S)-4, an advanced intermediate in the synthesis of idarubicinone, was thus raised by about 10%.