Nonstereospecific 1,3-Dipolar Cycloaddition Reactions of Azomethine Ylides: Proof of the Structures for Four Diastereoisomeric [3+2] Cycloadducts

Racemic azomethine ylides [(I) or (IV)] have been found to undergo cycloaddition to a trans-enamine [(II)] in a nonstereospecific way to yield mixtures of racemic diastereoisomeric 1:1 adducts: 5-dimethylamino-1,1,6-trimethyl-2,6a-di-p-tolyl-1,1a,5,6,6a,6b- hexahydro-4H-3,3a-diazacyclopropa[e]indene-4,4-dicarbonitrile, C₂₉H₃₃N₅ [(IIIa) and (IIIb)], or 2-dimethylamino-1,5,5-trimethyl-6-(4-methylbenzoyl)-7a-p-tolyl- 2,3,5,7a-tetrahydro-1H-pyrrolizine-3,3-dicarbonitrile (pyrrolizine is pyrrolo[1,2-a]pyrrole), C₂₉H₃₂N₄O [(Va) and (Vb)]. Crystal structure analyses prove the structures and configurations for three diastereoisomeric adducts (IIIa), (IIIb) and (Vb) unequivocally. In all three cases, the dimethylamino group appears endo at the five-membered ring formed in the cycloaddition step. In (cis-1a-cis-4a-transoid-8a,8b-transoid-8b,8c)-1,1-dimethyl- 4a-(pyrrolidin-1-yl)-2,8b-di-p-tolyl-1,1a,4a,5,6,7,8,8a,8b,8c-decahydro-4H-3,3a-diazacyclopropa[c]fluorene-4,4-dicarbonitrile, C₃₄H₃₉N₅, (VII), the cycloadduct formed using an azomethine ylid [(I)] and a cyclic enamine [(VI)], the aminofunction is again found in an endo position.