Isoproprenyl acetate

The lipase-ruthenium-catalysed DKR of other functionalised alcohols, such as diols, has been widely studied by Backvall s group in recent years." These authors have developed a highly efficient synthesis of enantiopure diacetates of the symmetric diols, 2,4-pentanediol and 2,5-hexanediol, by combining a ruthenium catalyst with lipase CAL-B in the presence of vinyl acetate or isoproprenyl acetate as the acyl donor, respectively. Excellent yields, and diastereo-and enantioseleetivities were obtained in both cases, as shown in Scheme 4.23. 

The reaction was performed with CAL-B in the presence of isoproprenyl acetate as the acyl donor in toluene. This new catalyst showed a higher stability combined with an improved performance as an alcohol racemisation catalyst in comparison with its well-known analogue, Backvall s catalyst. The enhanced stability of this catalyst compared with Backvall s catalyst could be related to the better shielding of the metal centre towards hydrolysis, thus hindering catalyst decomposition. As shown in Scheme 4.34, the corresponding acetates were obtained in high to excellent yields and excellent enantioselectivity of >97% ee. 

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