Synthesis and characterization of some oxidized derivatives of citronellal ethylene acetal

Article abstract of DOI:10.1139/v82-256

Three pairs of geometrical isomers corresponding to allylic monooxidation products of the trisubstituted olefin, citronellal ethylene acetal (3), were synthesized.These compounds were the E and Z isomers of 7-(1,3-dioxolan-2-yl)-2,6-dimethyl-2-hepten-1-ol, -1-al, and -1-oic acid (methyl ester), precursors for identifying the biodegradation products from citronellal and some of its derivatives.The E aldehyde (4) was obtained from 3 by the Sharpless procedure with catalytic quantities of selenium dioxide.The E ester (5) and E alcohol (6) were prepared in high isomeric purity (97-99percent) from 4 with activated manganese dioxide and sodium borohydride, respectively.Selective ozonolysis of the isobutenyl group in 3 gave 5-(1,3-dioxolan-2-yl)-4-methyl-1-pentanal (7).Under the conditions used, ozone did not react with the ethylene acetal group.Acetal aldehyde (7) was stereoselectively converted to the Z alcohol (8) by a Wittig reaction.Manganese dioxide oxidation of 8 (98-99percent Z isomer) to the Z aldehyde (9) and of 9 to the Z ester (10) was accompanied by partial Z to E isomerization.The distribution of E and Z isomers in crude reaction mixtures was determined by gas chromatography with a glass capillary column or by proton magnetic resonance spectroscopy.