| Popis: |
The basic reagent vinyloxyethoxy titanium trisisopropyloxide, easily modified by replacing two of the isopropyloxides with the optically active diol ( R )- or ( S )-BINOL, reacts with simple, prochiral aldehydes to give chiral β-hydroxy-1,3-dioxolanes with enantiomeric ratios up to 99:1. The same reagents, ( R )- or ( S )-configured, react with the chiral 2,3- O -isopropylidene- d -glyceraldehyde to give the corresponding open chain pentose derivatives. The main components have opposite descriptors at the newly created stereogenic center, indicating strong reagent control. A comparable system, modified by ( R , R )- or ( S , S )-TADDOL shows a weaker induction with the chiral aldehyde, but now with the same product configuration for both reagents, indicating predominant substrate control. |
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