ALLYLIC MONO-HYDROXYLATION AND DI-HYDROXYLATION OF ISOLATED DOUBLE-BONDS WITH SELENIUM DIOXIDE-TERT-BUTYL HYDROPEROXIDE - NMR CHARACTERIZATION OF LONG-CHAIN ENOLS, ALLYLIC AND SATURATED 1,4-DIOLS, AND ENONES

Selenium dioxide with tert-butyl hydroperoxide as re-oxidant was used in the allylic hydroxylation of isolated double bonds in straight-chai n hydrocarbons. This was shown for mono-unsaturated fatty acids, ester s and alcohols. Either allylic position was hydroxylated individually or both positions reacted to give dihydroxy isomers, affording numerou s novel hydroxy compounds. Yields of monohydroxy compounds in which th e OH group is between the double bond and C-1 were usually higher than those in which the OH group is between the double bond and the methyl terminus. Monohydroxy products were used as starting material in subs equent allylic hydroxylation reactions to increase the yield of dihydr oxy product, although this reaction is slow. Coinciding with the known mechanism, cis double bonds of starting materials isomerized nearly q uantitatively to trans double bonds in the products while trans double bonds did not isomerize. Resonance differences of the olefinic carbon s in C-13 NMR of the unsaturated monohydroxy compounds show on which s ide of the double bond the hydroxy group is located. The magnitude of these differences depends on the nature of the group at C-1 and the di stance of the double bond from C-1. Corresponding saturated hydroxy fa tty acids were synthesized with the hydrazine-air system. C-13 NMR of the saturated compounds showed that the dihydroxy products were erythr o/threo diastereoisomers. With this assignment, H-1 NMR of the unsatur ated allylic dihydroxy compounds may be used to distinguish these dias tereoisomers. The olefinic protons of the erthryo dihydroxy diastereoi somer resonate downfield from those in the threo form. The threo diast ereoisomers are formed in higher yields than their erythro counterpart s. Compounds with allylic keto group (enones) analogous to the monohyd roxy products arose as side products. The C-13 NMR spectra of these en ones are discussed.