Selectivity dihydroxylation

Glycals can be transformed into 1,6-anhydro sugar derivatives by intramolecular cyclization in the presence of Lewis and Brpnsted acids, a reaction that has been termed the intramolecular Ferrier glycosylation.168 Sharma el al.169 showed that a montmorillonite clay-supported silver reagent can be an efficient catalyst for this transformation. The 1,6-anhydro-2,3-dehydro sugars obtained were then selectively dihydroxylated to furnish 1,6-anhydro saccharides. 

Polyhydroxylated piperidines such as are of interest as glucosidase inhibitors. Antoni Riera, also of the University of Barcelona, has developed (J. Org. Chem. 2005, 70,2325) a route to 16 from the readily-available enantiomerically-pure epoxide 11. Condensation with ally isocyanate 12 followed by cyclization gave 13, which was further cyclized by a Grubb s catalyst (unspecified) to 14. Protection set the stage for face-selective dihydroxylation, to give 15. Several other piperidines having other polyhydroxylation patterns were also prepared from 14. 

Unsaturatcd carboxylic acids arc selectively hydroxylated on the double bonds. Pentafluoro-prop-1-enyl)malonate is selectively dihydroxylated by potassium permanganate on the fluorinated carbons. The intermediate geminal fluorohydrins 3 immediately eliminate hydrogen fluoride to give dioxo esters, such as 4, as the final product (vide supra).90... 

The proper choice of stoichiometric oxidant allows either syn-or anft -selective dihydroxylations. NaI04 as the oxidizing agent generates H20 as a side product of the oxidation and therefore enables the Woodward Reaction to take place. 

It has been demonstrated that by alteration of regio- and stereoselective epox-idation, then hydrolytic opening, and selective dihydroxylation, a variety of different yet stereochemically defined carbasugars and aminocyditols can be produced from enantiopure 2,3-trans-CHD. 

It has been shown that the phosphonodifluorodithioacetate (339) acts as a powerful heterodienophile and can be used to prepare a new class of phos-phonodifluoromethyl thiopyrans (340). These adducts can be submitted to a selective dihydroxylation to produce diastereoisomers (341) (an example is given in Scheme 9l)P ... 

SCHEME 13.51 Schreiber s synthesis of (—)-hikizimycin featuring a two-directional chain-elongation strategy involving an aldehyde olefination and face-selective dihydroxylations. 

Corey, E. J., Zhang, J. Highly Effective Transition Structure Designed Catalyst for the Enantio- and Position-Selective Dihydroxylation of Polyisoprenoids. Org. Lett. 2001, 3, 3211-3214. 

Dihydroxylation. Baylis-Hillman adducts undergo yyn-selective dihydroxylation. 

The indolizidine alkaloid swainsonine 412, a potential anticancer drug, has been the target of a number of syntheses. Pearson [99] started with 2,3-O-isopro-pylidene-D-erythronolactone 413, which afforded in three steps the allyUc alcohol 414. This compound was in turn submitted to Claisen-Johnson rearrangement and afforded ester 415. Selective dihydroxylation followed by functional group manipulations led to the target alkaloid (Scheme 6.68). An aminyl radical cycHza-tion was the key step in an ant venom alkaloid 416 synthesis [100]. The Claisen-Johnson rearrangement was used in the preparation of both side chains of this pyrroUdine alkaloid (Scheme 6.68). 

Nucleophilic attack by bicarbonate onto a dienyl complex 10.118 with an ester substituent also proceeded regioselectively. Starting from the resolved complex, methyl shikimate 10.122 could be prepared in optically active form using this reaction (Scheme 10.30). Protection of the alcohol and decomplexation gave the free diene 10.121, which underwent selective dihydroxylation trans to the TBS ether. Desilylation gave the natural product ester 10.122. 

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