Reactions of pyrrolidine enamines of cyclic and acyclic 3,4-dioxobutanoic acid derivatives with dimethyl acetylenedicarboxylate. A new case of atropoisomerism

Article abstract of DOI:10.1016/S0040-4020(01)85693-3

Reaction conditions and structure of the starting enamines (cyclic or open-chain) determine greatly the final products of the title reactions. Whereas in benzene and acetonitrile, DMAD and 1 give a mixture of the diastereoisomeric dienamines 5, in methanol they afford pirrolizine 3. Enaminofuranones 2 and 10 furnish in the corresponding 'Michael adducts' 7a,b,c and 11a,b,c but fail to yield pirrolizines. It has been demonstrated that above b and c adducts differ exclusively on the arrangement of groups around a chiral axis.