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The First Catalytic, Diastereoselective, and Enantioselective Crossed-Aldol Reactions of Aldehydes We are grateful to the National Science Foundation for generous financial support (NSF CHE 9803124).

The apotheosis of the aldol addition reaction is one of the most well-documented chapters of modern organic synthesis; the generality, versatility, and selectivity associated with this process have been the subject of countless reviews and authoritative summaries. Stimulated by the challenge posed by nature, a generation of synthetic organic chemists has constructed an impressive edifice of knowledge which constitutes insightful, elegant, and practical solutions to the structural and stereochemical problems presented by polypropionate-derived natural products. Yet, at this advanced vantage, it is remarkable that the most basic of aldol scaffold can be efficiently accomplished according to the Woerpel procedure employing the use of basic tBuOOH in DMF.[16] Several representative tetraols 12 were prepared in good yields with complete overall diastereoselectivity illustrating the generality of this strategy (Table 2). The occurrence of a polyol motif 12 in a number of bioactive natural products is noteworthy. Representative examples include the side chain portion of bacteriohopanoid.[17a] and the central macrolide segment of herbarumin I, a highly potent phytotoxic agent.[17b] In summary, we have demonstrated a highly enantioselective catalytic isomerization of silacyclopentene oxide, a pivotal point in our strategy for the stereoselective assembly of acyclic polyols. Development of an arsenal of new asymmetric processes utilizing cyclic silanes is currently in progress.