PERICYCLIC AND HETEROELECTROCYCLIC MECHANISMS FOR THE CYCLIZATION OF 1,3,5-HEXATRIEN-1-ONE AND ITS 6-AZA ANALOG
Keywords:
1H-pyridin-2-one, cyclohexa-1,3-dien-5-one, heteroelectrocyclization, quantum-chemical calculations, pericyclic reactions, 1,6-cyclizations]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.
How to Cite
Bakulev, V. A.; Subbotina, Yu. O.; Fabian, V. M. F. Chem. Heterocycl. Compd. 2003, 39, 1504. [Khim. Geterotsikl. Soedin. 2003, 1707.]
For this article in the English edition, see DOI 10.1023/B:COHC.0000014416.75284.9d
