In this work, a racemization method of (S)-1-phenylethanol by niobium salts was developed. Among the salts available, the niobium phosphate hydrate (NbOPO4.nH2O) reduced the enantiomeric excess (ee) of the chiral alcohol from 95 to 0% after 24 h at 60 ºC in toluene. This new racemization agent was combined with a lipase (CALB) in order to achieve a chemoenzymatic dynamic kinetic resolution (DKR). Experiments demonstrated that the DKR process is feasible and the corresponding (R)-1-phenylethyl acetate was obtained with 92% conversion and 85% ee.
Intrigued by the recent discovery of caramboxin by Brazilian researchers, we present the results from our studies toward the racemic synthesis of caramboxin analogs through the orthocarboxylation of 3,5-dimethoxy benzyl derivatives. Three different approaches were tested, and the route involving a Vilsmeier-Haack formylation followed by a Lindgren oxidation provide a potential intermediate for the synthesis of several caramboxin analogs.
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