Diastereoselective addition of metal-coordinated and “naked” nucleophilic reagents to norephedrine derived 2-acyl-N-tosyl-oxazolidines
1997; Elsevier BV; Volume: 53; Issue: 5 Linguagem: Inglês
10.1016/s0040-4020(96)01087-3
ISSN1464-5416
AutoresGiovanni Poli, E. MACCAGNI, Leonardo Manzoni, Tullio Pilati, Carlo Scolastico,
Tópico(s)Cyclopropane Reaction Mechanisms
ResumoAbstract 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 π-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 reamarkable Si and Re π-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 chelated mode of addition of these nucleophiles in the absence or in the presence of chelating metal counterions respectively. The addition of nucleophilic reagents to the 2-acetyl-1,3-oxazolidine could be directed with high selectivity to either the Si or the Re π-carbonyl face under chelating or non-coordinating conditions respectively.
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