Diols with ceric ammonium nitrate

Reaction of 61 with ethylmagnesiiun chloride in THF at -78 °C was fully stereoselective yielding a single product that furnished hydroxyketone 58 after hydrolysis. Reduction of 58 with potassiiun borohydride gave a mixtine of diols in the ratio 15 2, from which a major isomer was isolated by column chromatography and oxidized with ceric ammonium nitrate (CAN) to quinone 62 in 40% overall yield (Scheme 13). 

The use of ceric ammonium nitrate (Ce ) in the elucidation of structure of bis-benzyhsoquinoline alkaloids appeared some 7 years after the introduction of photo-lytic oxidation. In a similar manner to photo-oxidation, oxidation of tetrandrine (16) with ceric ammonium nitrate afforded, after workup with sodium borohydride, the diamine (17) (95%) and the diol (18) (90%) (Bick et al. 1978) (Fig. 5). 

Ceric ammonium nitrate appears to be a valuable reagent for dehydrogenation of bisbenzylisoquinoline alkaloids. For example, oxidation of tetrandrine (48) with 8 mol of this reagent in buffered HOAc, followed by NaBH4 reduction of the intermediate imine 381, gave a 95% yield of diamine 382, as well as the crystalline diol 383. Similarly successful results were obtained with heman-dezine (24a) and O-methylmicranthine (384), the latter demonstrating that this procedure is compatible with secondary amino groups. Berbamine (364),... 

Two oxidants essentially dominate these oxidations lead tetraacetate in organic solvents and periodic acid in aqueous media. On occasion, other oxidation reagents cause the cleavage of vicinal diols ceric ammonium nitrate [424], sodium bismuthate [482, 483], chromium trioxide [482, 555], potassium dichromate with perchloric acid [949], manganese dioxide [817], and trivalent [779, 789] or pentavalent [798] iodine compounds. 

Thus, the aldol shown, which is susceptible to Sharpless-type epoxidation, has been obtained from phytal and the protected hydroquinone (ref. 120). Formation of the epoxide presumably with a chiral peracid (or perhaps with a conventional peracid relying on the asymmetry of the substrate) and then cleavage reductively in t-butyl methyl ketone containing lithium aluminium hydride led to a diol. The benzylic hydroxyl group of this was hydrogenolysed to afford the hydroquinone dimethyl ether in 85% yield. Ceric ammonium nitrate (CAN) oxidation afforded the intermediate benzoquinone hydrogenation of which was reported to result in 2R,4 R,8 R-a-tocopherol by, presumably, avoidance of a racemisation step. 

Oestrone acetate treated 40 min. at room temp, with 4 moles ammonium ceric nitrate in aq. 90%-acetic acid 9a,ll -diol 11-nitrate. Y 69%. F. e. s. P. J. Sykes et al., Tetrah. Let. 1971, 3393 oxidations with cerium(IV) salts, review, s. T.-L. Ho, Synthesis 1973, 347. 

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