Asymmetric epoxidation mismatched double

The idea of double asymmetric induction is also applicable to asymmetric epoxidation (see Chapter 1 for double asymmetric induction). In the case of asymmetric epoxidation involving double asymmetric induction, the enantiose-lectivity depends on whether the configurations of the substrate and the chiral ligand are matched or mismatched. For example, treating 7 with titanium tet-raisopropoxide and t-butyl hydroperoxide without (+)- or ( )-diethyl tartrate yields a mixture of epoxy alcohols 8 and 9 in a ratio of 2.3 1 (Scheme 4 3). In a... 

We began these studies with the intention of applying this tandem asymmetric epoxidation/asymmetric allylboration sequence towards the synthesis of D-olivose derivative 63 (refer to Figure 18). As the foregoing discussion indicates, our research has moved somewhat away from this goal and we have not yet had the opportunity to undertake this synthesis. This, as well as the synthesis of the olivomycin CDE trisaccharide, remain as problems for future exploration. Because it is the enantioselectivity of the tartrate ester allylboronates that has limited the success of the mismatched double asymmetric reactions discussed here, as well as in several other cases published from our laboratorythe focus of our work on chiral allyiboronate chemistry has shifted away from synthetic applications and towards the development of a more highly enantioselective chiral auxiliary. One such auxiliary has been developed, as described below. 

Scheme 1.6. Matched and mismatched double asymmetric induction demonstrating Reagent-Based Stereocontrol (a) The diethylzinc addition catalyzed by titanium TADDOLates (Chapter 4, [52]). (b) The Sharpless asymmetric epoxidation (Chapter 8,...

Representative examples are shown in Scheme 9. The Sharpless AE of geraniol (57) with (+)-diethyl tartrate (DET) gave a-epoxide 58 with 95% ee. In a double asymmetric induction, epoxidation of allylic alcohol 59 with (—)- and (+)-DET provided a- and P-epoxides, 60 and 61, in ratios of 40 1 and 1 14, respectively [23]. It is noteworthy that high asymmetric selectivity was induced even in the mismatched case. The Sharpless AE is also effective for the kinetic resolution of racemic allylic alcohols. In the reaction of 62 with 0.6 equiv. of t-BuOOH and... 

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