Thiophene alcohols kinetic resolution

In practice, oxidations of this type have been observed and generally have been carried out with a substrate bearing a racemic secondary alcohol so that kinetic resolution is achieved. Although these oxidations are not strictly within the scope of this chapter, they are summarized briefly in Eqs. 6A.7-6A.9 to acquaint the reader with other potential uses for the Ti-tartrate catalytic complex. In the kinetic resolutions shown in Eqs. 6A.7 and 6A.8, the oxidations are controlled by limiting the amount of oxidant used to 0.6 equiv. Only modest resolution was attained for the acetylenic alcohol (Eq. 6A.7, 21% ee) [77] and the allenic alcohol (Eq. 6A.8, 40% ee) [77]. Resolutions of the furanols [142] or the thiophene alcohols [143] of Eq. 6A.9 generally are excellent (90-98% ee except when Rj is a I-butyl group). Only in the kinetic resolution of the furanols has the oxidation product been identified and, in that case, is a dihydropyranone. 

Heterocyclic compounds such as furan, thiophene, and pyrrole are subject to oxidation. Similar to secondary allyUc alcohols, 2-(l-hydroxyalkyl) derivatives of these heterocychc compounds are also good substrates for kinetic resolution using a titanium-tartrate and TBHP system (Scheme 15). 

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