Peroxy acids anti hydroxylation

With one exception—when the substituent is a hydroxyl group. When an allylic alcohol is epoxidized, the peroxy-acid attacks the face of the alkene syn to the hydroxyl group, even when that face is more crowded. For cyclohexenol the ratio of syn epoxide to anti epoxide is 24 1 with m-CPBA and it rises to 50 1 with CF3CO3H. 

In Problem 7.11 we saw that hydroxylation with permanganate is syn, and hydroxy lotion with peroxy acids is anti. Keeping in mind that reaction of epoxides (Sec. 17.12 is acid-catalyzed, give a detailed mechanism for hydroxylation with peroxy acids. (Ch your answer in Sec. 17.12.)... 

In ketone-directed peroxy acid epoxidations of cyclic alkenes the actual epoxidizing agent has been shown by 180-labeling not to involve a dioxirane <94TL6155>. Instead, an a-hydroxy-benzoylperoxide or a carbonyl oxide is believed to be responsible for observed stereoselectivities in the intramolecular epoxidations. The extent of syn-selectivity is greater for ketones than with esters the syn/anti ratios increase when ether is used as solvent rather than CH2C12, the reverse situation for hydroxyl-directed epoxidations. Fused-ring oxiranes can also be prepared from acyclic precursors. Four different approaches are discussed below. 

When an alkene is reacted with the peroxy acid (1) In aqueous acetone, the anti hydroxylation product is obtained direcdy. Cyclohexene (8) is converted to the trans-dioX (9) (eq 3). Reagent (1) has been used for the synthesis of ( ) y-rhodomycinone (11) via frans hydroxylation of the alkene (10) (eq 4). ... 

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