Preparation, Structure, and Unique Thermal [2+2], [4+2], and [3+2] Cycloaddition Reactions of 4Vinylideneoxazolidin‐2‐one

Abstract
The terminal allene CαCβ bonds of 4vinylidene-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 3substituted (Z)-methylenecyclobutenes 6, 3substituted methylenecyclobutanes 7 and 8, and 3vinylmethylenecyclobutanes 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 [(π2s2s)allene + π2s] Hückel 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.

This publication has 144 references indexed in Scilit: