Studies on cyclitols-XV. The mechanism of trans-hydroxylation of conjugated dienes by permanganate

When 1,3-cyclohexadiene 1 and cyclopentadiene 12 are treated with neutral or alkaline permanganate, two sets of products are formed in each case. One set of products is formed by normal hydroxylation, and consists of the respective dl-cis-1,2-cycloalkenediols 3 or 14, and the corresponding dl-(1, 2 3,4)-cycloalkane-1,2,3,4- 6a and 11. The other set of products is formed by abnormal hydroxylation, and consists chiefly of the all-cis-dl-1,2-anhydro-1,2,3,4 tetrols 2 and 13, and the dl-(1,2, 3 4)-cycloalkane-1,2,3,4-tetro 4a and 15. Small amounts of the dl-(1,2, 4 3)-cycloalkane-1,2,3,4-tetrols 5 and 16 are also formed. The abnormal pathway predominates in the cyclopentanoid series, but substantial amounts of both sets of products are always formed. The ratios of (1,2, 3 4)-tetrol to (1,2, 4 3)-tetrol obtained by the hydroxylation procedure are approximately the same as the ratios of these compounds formed by hydrolysis of the anhydrotetrols in dilute acid. It is proposed (1) that the anhydrotetrols or reactive intermediates related to them are intermediates in the abnormal tetrahydroxylation; and (2) that the cis-cycloalkenediols are intermediates in the normal but not the abnormal hydroxylation, nor in the formation of the anhydrotetrols. By treatment with NaN₃ and subsequent acetylation, the anhydrotetrol 2 has been converted into dl-(1,2, 3 4)-1,2,3-tri-O-acetyl-4-azidocyclohexane-1,2,3-triol 22b; catalytic reduction of 22b followed by acetylation gives dl-(1,2, 3 4)-4-acetamido-1,2,3-tri-O-acetylcyclohexane-1,2,3-triol 23b. Treatment of 2 with HBr produces a dl-bromocyclohexanetriol 20 or 21, whose structure and configuration have not yet been established.