ON THE MECHANISM OF FORMATION OF GLYCOFURANO[2,1-D]-IMIDAZOLIDIN-2-ONES - REACTION OF 2-AMINO-2-DEOXYHEPTOPYRANOSES WITH ISOCYANATES

Reaction of 2-aminosugars with isocyanates has been extended to other higher-carbon sugars. Ureido derivatives or, in most cases, monocyclic structures can be easily isolated. Importantly, the last substances display a relative trans disposition between the substituents at C-4 and C-5 of the heterocyclic ring, as a consequence of a rapid cis-trans isomerisation in acidic media. This stereochemical feature ensures (he stereocontrolled ring closure to give exclusively cis-fused glycofuranose systems. In the light of these results, some related reactions have been revised.