Optically pure available lactones 1 and 5 were diastereoselectively oxidised to cis-diols 2 and 6 by KMnO4 and to epoxides 3 and 7 by 3-chloroperoxybenzoic acid. Epoxide 3 was cleaved to trans-diol 4, whereas hydrolysis of 7 afforded tricyclic carboxylic acid 8. Optically pure dihydroxylactones 2, 4, and 6 are valuable models for structure determination of the antimicrobial garlic component garlicin.