CHELATION CONTROLLED ALDOL ADDITIONS OF THE ENOLSILANE DERIVED FROM TERT-BUTYL THIOACETATE - A STEREOSELECTIVE APPROACH TO 1-BETA-METHYLTHIENAMYCIN

The tert-butyldimethylenolsilane derived from tert-butyl thioacetate is a useful reagent for highly stereoselective chelation-controlled additions to chiral \u3b1-alkoxy and \u3b1-methyl-\u3b2-alkoxy aldehydes where the corresponding acetate fails. The aldol product deriving from the TiCl4 mediated addition to \u3b1-methyl-\u3b2-alkoxy aldehyde 5 was elaborated In high yield to give the bicyclic \u3b2-lactam 11, an Intermediate for the preparation of 1\u3b2-methylthienamycin. Problems associated with the partial racemlzation of aldehyde 5 during the TiCl4 mediated condensations have not yet been completely resolved