32376-01-5Relevant articles and documents
Preparation, structure, and unique thermal [2 + 2], [4 + 2], and [3 + 2] cycloaddition reactions of 4-vinylideneoxazolidin-2-one
Horino, Yoshikazu,Kimura, Masanari,Tanaka, Shuji,Okajima, Toshiya,Tamaru, Yoshinao
, p. 2419 - 2438 (2007/10/03)
The terminal allene Cα=Cβ bonds of 4-vinylidene-2-oxazolidinone (2) readily undergo [2 + 2] cycloaddition with a wide variety of terminal alkynes, alkenes, and 1,3-dienes irrespective of their electronic nature under strictly thermal activation conditions (70-100°C) and provide 3-substituted (Z)-methylenecyclobutenes 6, 3-substituted methylenecyclobutanes 7 and 8, and 3-vinylmethylenecyclobutanes 9, respectively, in good to excellent yields. Alkenes react with 2 with complete retention of configuration. The [2 + 2] cycloaddition is concluded to proceed via a concerted [(π2s + π2s)allene + π2s] Hueckel transition state on the basis of experimental evidences and quantum mechanical methods. Some highly polarized enones and nitrile oxide, on the other hand, react with 2 selectively at the internal C4=Cα double bonds and give spiro compounds 10 and 11, respectively. The bent allene bonds (173-176°) and the unique reactivity associated with 2 are attributed to a low-lying LUMO (Cα=Cβ) that is substantiated by a through-space σ*(N-SO2)-π*(Cα= Cβ) orbital interaction.
