Methyl dimorphecolate (methyl 9(S)-hydroxy-10, 12-E,E-octadecadienoate) (1) was converted to resp. 9-methoxy (2), 9-trimethylsiloxy (3), 9-acetoxy (4), 9-chloroacetoxy (5) derivatives with reaction conditions optimized to high yields. The dienes were epoxidized with m-chloroperbenzoic acid to mono-oxiranes with excellent conversion (ratio C10-C11 epoxy to C12-C13: 90:10 for 9-hydroxy; 12:88 for 9-methoxy; 26:74 for 9-siloxy; 16:84 for 9-acetoxy; 17:83 for 9-chloroacetoxy). Methanolysis of a mixture of 9-chloroacetoxy oxiranes gave the 9-hydroxy mixture with 19:81 proportions of isomers. Analysis was based on 1H and 13C NMR-spectrometry including 2D techniques.