| Glucose-derived chiral ketones have been employed in the epoxidation of conjugated dienes to synthesize vinyl cis-epoxides with high chemo- and enantioselectivity. The reactions are stereospecific in that cis-olefins yielded only cis-epoxides with no isomerization observed. The enantioselectivity of the reaction is highly dependent on the substitution pattern of the diene with cis/trans -dienes being the most effective. With this methodology a variety of synthetically useful enantioenriched vinyl epoxides are now readily accessible.; An effective system for the asymmetric epoxidation of conjugated cis-enynes has been developed using glucose-derived chiral ketones and Oxone as oxidant. The reactions are highly chemoselective and stereoselective and are stereospecific. In addition to the directing effect of the alkyne, hydrophobic interactions between the catalyst and substrate play an important role in stereodifferentiation. These insights will be useful for expansion of this methodology to other substrate classes, the prediction of the stereochemical outcome of a given reaction, and the design of new ketone catalysts.; A convenient method for the asymmetric epoxidation of cis-olefins using glucose-derived oxazolidinone-containing chiral ketones with H 2O2 as stoichiometric oxidant has been developed. Use of H2O2 as oxidant rather than Oxone allows for use of less solvent and salts, and eliminates the need for slow addition of oxidant. The reactions are operationally simple, and in most cases give results similar to those obtained with Oxone.; The scope of the ketone-catalyzed asymmetric epoxidation reaction has been expanded to include several types of unconjugated cis-olefins. With this system it is possible to use substituent polarity as an effective method of stereodifferentiation between two prochiral faces of an olefin. Allylic oxygen functionality also provides a mechanism for stereodifferentiation, although further experimentation is needed to define this mechanism clearly. This study opens up a new avenue of potential for this catalyst system. |
