Abstract
The thermal reactions of the 2,2,3-tri-substituted 1-phthalimidoaziridine 1a with dimethyl acetylenedicarboxylate (DMAD), thioketones 4a – 4d, and dimethyl azodicarboxylate (5) proceed even at room temperature leading to the five-membered cycloadducts 2a, 6 – 8, and 12, respectively, with retention of the spatial arrangement of the aziridine substituents, in contrast to the expectation based on the conservation of orbital symmetry in concerted reactions. The analogous reactions of the tetra-substituted phthalimidoaziridine 1b with thioketones at 40° lead to the 1,3-thiazolidine derivatives 10 and 11 as mixtures of diastereoisomers. These unexpected results may be explained by either the isomerization of the intermediate azomethine ylides or a non-concerted stepwise cycloaddition of these ylides with the dipolarophiles. The structures of some adducts have been determined by X-ray crystallography.
Ushkov, A V