Zinc bromide as catalyst for the stereoselective construction of quaternary carbon: improved synthesis of diastereomerically enriched spirocyclic diols

Zinc bromide (ZnBr2) has proved to be a facile and efficient catalyst for t he stereoselective semipinacol rearrangement of alpha -hydroxy epoxides at room temperature. Of note are the presence in the product of two adjacent c hiral carbon centers, particularly the creation of a stereoselective quater nary center, and the efficient synthesis of beta -hydroxy ketones, includin g some with naturally occurring spiroalkane skeletons. As an example of its application, important diastereomerically enriched spirocyclic diol ligand s have been synthesized conveniently via this rearrangement followed by red uction of the spirocyclic beta -hydroxy ketones obtained with appropriate h ydride reagents.