Acetals, chiral

Finally, the necessity arose for the synthesis of pentulose 21, labeled with, 3C on the central carbons, C-2 and C-3, for an independent biosynthetic study, which is reported in Section III.5.27 The doubly labeled ester 34 (Scheme 14) is readily available by a Wittig- Homer condensation of benzyloxyacetaldehyde with commercially available triethylphosphono-(l,2-l3C2)acetate. Chirality was introduced by the reduction of ester 34 to the allylic alcohol, which produced the chiral epoxide 35 by the Sharpless epoxidation procedure. This was converted into the tetrose 36, and thence, into the protected pentulose 37 by the usual sequence of Grignard reaction and oxidation. 

Triphenylbismuth(V) diacetate acts as O-phenylating agent of alcohols. The reaction of ci s-l, 2-cyclopentanediol catalyzed by a Cu(II) acetate-chiral pyridinyloxazoline combined system gives the mono-phenylation product in up to 50% ee (Scheme 127) (307). 

Pummerer reaction. Upon reaction with a-ethoxyvinyl acetate chiral sulfoxides in which the a-carbon is substituted with an electron-withdrawing group are transformed into a-acetoxy sulfides. In most cases the enantiomer excess of the products amount to 70-80%. 

Feldberg and Reppucci developed a novel separation of anomeric alpha (pharmacologic) purines carried out by copper acetate chiral plates. Solvents were methanol-water-ACN. Visualization occurred through UV. Graphs were plotted based on alteration of ACN percentages. 

Keywords Garb ohydrates, ReetfrEuigements, Enol ethers, Ketene acetals. Chiral building blocks... 

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