The asymmetric [2+2]cycloadditions of chlorosulfonyl isocyanate to vinyl et
hers derived from sugars and hydroxy acids are presented. The account focus
es on various aspects of the cycloaddition and on the transformations of th
e resulting [2+2]cycloadducts into clavams and 1-oxacephams. In order to ra
tionalize the results of direction and magnitude of [2+2]cycloaddition, the
stereochemical models of this reaction are discussed.