Vitamin epoxide ring opening

Application of the above mentioned epoxy sulfone cyclization reaction has been ingeniously used in a synthesis of muscone (Scheme 113, entries c and d) and also of vitamin D3 (Scheme 113, entry e)/ In the latter case surprisingly the terminal epoxide, when subjected to the intramolecular cyclization gave a mixture of sulfonylcyclopentane and sulfonylcyclohexane derivatives arising respectively from the epoxide ring opening at the most (30%) and the least (50%) substituted carbons. ... 

The presence of a hydroxyl group at the 1 position (steroid numbering), which also occurs in a vitamin D metabolite, also enhances potency. The synthesis in this case starts with an advanced ring opened intermediate (36-5) already provided with that extra hydroxyl group [30]. Constmction of the side chain begins with condensation of the ylide from phosphonium salt (36-1) with pivalaldehyde. The ketone in the product (36-2) is then reduced to the alcohol (36-3). The olefin is then epoxidized... 

In early vitamin and carotenoid syntheses, the oxidation of j6-isophorone was accomplished by epoxidation of /1-isophorone followed by tbe ring-opening of the epoxide and oxidation (Fig. 16.13). A significant improvement of the three-step synthesis of KIP was made by the one-step liquid phase oxidation of j6-isophorone using oxygen or an oxygen-containing gas in the presence of a transition metal catalyst. In 1975, the aerobic oxidation of j6-isophorone in tbe presence of Cu(II)-or V(III)-acetylacetonate was published, in which KIP was obtained in a yield of up to 55%. ... 

Oxoisophorone 68 can be converted into trimethylcyclohexanone (74), in a series of reduction and elimination steps [82], opening up a new route to p,p-carotene (3) and vitamin A [85,86]. The Cio-epoxide 75 can be obtained by Wittig olefination of 73 with methylene-triphenylphosphorane, isomerization and reaction with peracids. Lewis acid-catalysed rearrangement to give the five-membered ring yields the capsorubin synthon 76 [9]. 

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