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A new synthetic approach to 5-dethia-4-methyl-5-oxacephems |
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| Authors: | Zbigniew Ka?u?a Arkadiusz KazimierskiKrzysztof Lewandowski Kinga SuwińskaBeata Szcz?sna Marek Chmielewski |
| Affiliation: | a Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland b Institute of Chemistry, Podlasie University, 08-110 Siedlce, Poland c Institute of Physical Chemistry of the Polish Academy of Sciences, 01-224 Warsaw, Poland |
| Abstract: | Starting from (l)-ethyl lactate and 4-vinyloxy-azetidin-2-one the diastereomeric (4S,6R)- and (4S,6S)-4-methyl-5-oxa-3-methylene and 3-oxo-cephams were obtained. The formation of the cepham skeleton proceeds with a diastereomeric excess up to 80%, depending on catalyst and reaction conditions. For comparison, the corresponding racemic cephams lacking a methyl at C-4 or with a gem-dimethyl group at C-4 were synthesized. |
| Keywords: | 5-oxacephams iminium cation stereoselective cyclization |
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