ORGN 114 |
| Recently the electrocyclic ring closure of 7-azahepta-1,2,4,6-tetraene 1 to give 1-aza-6-methylidenecyclohexa-2,4-diene (2) has been studied at the B3LYP computational level of theory by two groups who came to quite different conclusions concerning the mechanistic roles played by the terminal allenyl C-C π-bond and the nitrogen lone-pair orbital (Rodriguez-Otero, J.; Cabaleiro-Lago, E. M. Angew. Chem. Int. Ed. 2002, 41, 1147/ de Lera, A. R.; Cossio F. P. Angew. Chem. Int. Ed. 2002, 41, 1150). We have now studied the 1→2 reaction and, for comparative purposes, the similar concerted electrocyclic ring closures of compounds 3 – 7, all at the CASSCF/6-31G* level. The evidence obtained from a careful study of the active space MOs and the vibrations of the imaginary frequencies of the transition structures (e.g., TS12) obtained for all these reactions appears to rule out any participation by the terminal C-C π-bond in the case of the 1→2 reaction. As for the nitrogen lone-pair orbital, it appears that it is to some degree involved in making the new C-N single bond in 2, but there is also evidence for the simultaneous participation of the π-orbital system in the process.
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Process R&D, Physical Organic Chemistry, Heterocycles, Aromatics, Metal-Mediated Reactions
8:00 PM-10:00 PM, Sunday, March 25, 2007 Hyatt Regency Chicago -- Riverside Center, Poster
Division of Organic Chemistry |
