The asymmetric [2+2]cycloadditions of chlorosulfonyl isocyanate to vinyl ethers derived from sugars and hydroxy acids are presented. The account focuses on various aspects of the cycloaddition and on the transformations of the resulting [2+2]cycloadducts into clavams and 1-oxacephams. In order to rationalize the results of direction and magnitude of [2+2]cycloaddition, the stereochemical models of this reaction are discussed.
Subsequent transformations of adducts consisting in detritylation, tosylation of a terminal hydroxy group and intramolecular alkylation of the nitrogen atom give corresponding tetracyclic 5-oxacephams.
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