Diastereoselective addition of metal-coordinated and “naked” nucleophilic reagents to norephedrine derived 2-acyl-N-tosyl-oxazolidines
摘要:
The addition of tri-s-butyl borohydrides to the 2-acetyl-1,3-oxazolidine 1 could be directed with high selectivity to either the Si or the Re pi-carbonyl face under chelating or non-coordinating conditions respectively. Addition of hydrides to the corresponding phenyl ketone 2 was 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 organomagnesium reagents follow the above trend. This data are in accord with a Felkin-type or a stereochemically opposite chelaled mode of addition of these nucleophiles in the absence or in the presence of chelating metal counterions respectively. (C) 1997, Published by Elsevier Science Ltd.
Diastereoselective addition of metal-coordinated and “naked” nucleophilic reagents to norephedrine derived 2-acyl-N-tosyl-oxazolidines
摘要:
The addition of tri-s-butyl borohydrides to the 2-acetyl-1,3-oxazolidine 1 could be directed with high selectivity to either the Si or the Re pi-carbonyl face under chelating or non-coordinating conditions respectively. Addition of hydrides to the corresponding phenyl ketone 2 was 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 organomagnesium reagents follow the above trend. This data are in accord with a Felkin-type or a stereochemically opposite chelaled mode of addition of these nucleophiles in the absence or in the presence of chelating metal counterions respectively. (C) 1997, Published by Elsevier Science Ltd.