DIASTEREOSELECTIVE ADDITION OF METAL-COORDINATED AND NAKED NUCLEOPHILIC-REAGENTS TO NOREPHEDRINE DERIVED 2-ACYL-N-TOSYL-OXAZOLIDINES

The addition of tri-s-butyl borohydrides to the 2-acetyl-1,3-oxazolidi ne 1 could be directed with high selectivity to either the Si or the R e pi-carbonyl face under chelating or non-coordinating conditions resp ectively. Addition of hydrides to the corresponding phenyl ketone 2 wa s highly Si selective only in the former conditions. Grignard reagents and organolithiums add to the methyl ketone 1 with remarkable Si and Re pi-face selectivity respectively. With phenyl ketone 2 only organom agnesium reagents follow the above trend. This data are in accord with a Felkin-type or a stereochemically opposite chelaled mode of additio n of these nucleophiles in the absence or in the presence of chelating metal counterions respectively. (C) 1997, Published by Elsevier Scien ce Ltd.