Tetramisole-based catalysts

Groger has also reported a preliminary study on enantioselective acetyl migration in the Steglich rearrangement using one of Fu s commercially available catalysts and Birman s tetramisole-based organocatalyst [108]. 

Figure 41.4 Structure of various tetramisole-based catalysts.

Subsequently, Shiina et al. developed a practical method for the KR of racemic carboxylic acids involving an achiral alcohol, PMBA or pivalic anhydride, and a tetramisole-based catalyst [56]. After an exhaustive parameter screen, it was shown that a combination of bis(a-naphthyl)methanol, pivahc anhydride, and (S)-P-Np-BTM (53) induced the best levels of selectivity at room temperature, affording the corresponding esters with high s factors ranging from s = 20 to 484 (Scheme 41.9). 

Subsequently, Birman et al. tested various amidine-based catalysts, including commercially available tetramisole (45) and its benzanneUated analog benzote-tramisole (BTM) (23) in the KR of secondary aryl aUcyl alcohols and propargyUc alcohols (Eigure 41.3). Both catalysts displayed far superior enantioselectivity although BTM proved to be more reactive [27c, 50, 51[. 

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