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- Title
Pericyclic and Heteroelectrocyclic Mechanisms for the Cyclization of 1,3,5-Hexatrien-1-one and Its 6-Aza Analog.
- Authors
Bakulev, V. A.; Subbotina, Yu. O.; Fabian, V. M. F.
- Abstract
The cyclization of 1,3,5-hexatrien-1-one, 1, and the Z- and E-isomers of 1-aza-1,3-butadienylketene 3 were studied using the semiempirical AM1 and PM3 methods. Cyclizations of compounds 1 and Z-3 are shown to occur via a mono-rotation mechanism with barriers of 15.49 and 32.85 kcal/mol respectively. The reactions proceed via non-planar transition states which result from rotation of the methylene group for compound 1 and the imino group for compound Z-3. Cyclization of E-3 proceeds via a non-rotatory mechanism through a planar transition state. The activation barrier is 4.83 kcal/mol (AM1). The electronic structures of the initial and final states, and of some intermediate structures, including the transition states for the cyclization of compounds 1 and 3, were analyzed by the natural orbital method using HF/6-31G*//AM1 calculations. Energetic, structural, and orbital criteria indicate the heteroelectric mechanism for the cyclization of compound E-3 and the pericyclic mechanism for the cyclization of compounds 1 and Z-3.
- Subjects
RING formation (Chemistry); CHEMICAL reactions; HETEROCYCLIC compounds; CARBENES; IMINO compounds
- Publication
Chemistry of Heterocyclic Compounds, 2003, Vol 39, Issue 11, p1504
- ISSN
0009-3122
- Publication type
Article
- DOI
10.1023/B:COHC.0000014416.75284.9d