A STRAINED AMINOAZONIATRICYCLENE SPECIES - RESULT OF AN INTRAMOLECULAR STABILIZATION OF A CYCLOPROPANIMINIUM ION BY AN AMINO MOIETY

Ab initio calculations of the cationic intermediates of a cyclopropane -forming process of 1,4-diamino-6-chlorocyclohexene precursors predict the 3 alpha-aminobicyclohexane-6-iminium ion 6c to be more stable tha n its 3 beta-isomer 7c. The latter, however, stabilizes itself by intr amolecular cyclization leading to aminoazoniatricyclene species 9c. Th e aminocyclohexenyl cation 8c proved to have no minimum on both the MP 2 and the MP4(SDTQ) potential energy surfaces. Optimization of species 8c causes a ring closure reaction to give iminium analogues 6c or 7c. The potential energy curve of this transformation 6c --> 8c --> 7c wa s calculated. Experimentally, solvolysis of chloro enamine isomers 4a and 5a was studied as a simple access to these cationic intermediates: 3 alpha-amino 6-iminium ion 6a leading to 3 alpha-amino 6-semiaminal 12 is generated exclusively from trans chloro enamine 4a and as main i ntermediate (67%) from cis chloro enamine 5a. In the latter case, amin oazonia compound 9a is formed as a byproduct (33%) which decomposes in water to give 3 beta-amino 6-semiaminal 13 via 3 beta-amino 6-iminium ion 7a. Aminoazoniatricyclene species 9a is obtained as stable tetraf luoroborate in acetonitrile or dichloromethane by reaction of chloro e namine isomers 4a or 5a with AgBF4-. H-1 and C-13 NMR spectral and X-r ay structural data are given for this strained tricyclic system 9a.