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Communication | Special issue | Vol 37, No. 1, 1994, pp.257-264
Published online, 1st January, 1970
DOI: 10.3987/COM-93-S51
Reaction of Aromatic N-Oxides with Dipolarophiles XIX. PM3 Analysis of Sequential Pericyclic Reactions between Pyridine N-Oxides and Allenes

Toshikazu Matsuoka, Kazunobu Harano, and Takuzo Hisano*

*Faculty of Pharmaceutical Sciences, Kumamoto University, 5-1 Oe-hon-machi, Kumamoto 862-0973, Japan

Abstract

Sequential pericyclic reactions between pyridine N-oxides and allenes were evaluated in terms of PM3 calculation. Structures corresponding to the perturbating system were calculated by varying the distance of the addends. The cycloaddition occurs via Π-complex. In the transition structure TS1 of primary cycloaddition, the lengths of the newly created bonds of O-C and C-C are 1.864 and 2.204 A, respectively. The bond between the O atom of pyridine N-oxide and the central carbon of allene is ca. 35 % formed at TS1, slightly advanced than the other (ca. 30 %). The PM3 calculation at the UHF level predicts that [1,5]-sigmatropic rearrangement of the primary cycloadduct proceeds via a transition state with a biradical character.