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1 2003

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Stereokontrolowana synteza tlenowych analogów penicylin i cefalosporyn

Łysek R., Furman B., Borsuk K., Chmielewski M.

Wiadomości Chemiczne

2003

[Z] 57, 5-6

391--433

Synthesis of oxacephalotin and oxacephamandol which are more active then natural, containing sulfur congeners, and isolation of clavulanic acid, a patent inhibitor of (3-lactamase enzymes, directed attention of academic and industrial laboratories to the synthesis of oxygen analogs of penicillins and cephalosporins. The present review directs attention to the stereocontrol of a desired configuration in the formation of the bridgehead carbon atom. Five possible methods leading to basic skeletons of the title compounds are discussed (Scheme 1). Three of them involve nucleophilic substitution at C-4 of the azetidin-2-ones performed as inter or intramolccular process, and two of them involve cycloaddition reactions between ketenes and iminoethers, or between vinyl ethers and isocyanates. Owing to the general application stereospecificity, and high asymmetric induction, the last method seems to be most advantageous. The weak point of the nucleophilic substitution methodology is that a nuclcophilc enters 3-substituted azetidin-2-one ring preferentially anti to the existing substituent or if there is no substitutent at C-3, stereoselectivity in generation of a new stereogcnic center at C-4 is low. All methods arc illustrated by examples taken from the literature.