Double diastereoselection in aldol reactions mediated by dicyclohexylchloroborane between chiral aldehydes and a chiral ethyl ketone derived from L-erythrulose.: Synthesis of a C1-C9 fragment of the structure of the antifungal metabolite Soraphen A1 α

Both matched and mismatched diastereoselections have been observed in the aldol reactions of a range of chiral aldehydes with the dicyclohexylboron enolate of a chiral ethyl ketone related to L-erythrulose. As was previously observed in the corresponding aldol reactions with L-erythrulose derivatives, the Felkin-Anh model provides an adequate explanation for the stereochemical outcome of reactions with chiral a-methyl aldehydes. However, a satisfactory account of the results observed with alpha-oxygenated aldehydes was only possible with the Cornforth model. As a practical application of the methodology described herein, a C-1-C-9 fragment of the structure of the antifungal macrolide soraphen A(1 alpha) has been prepared in a convergent and stereoselective way.