Reversible Intramolecular Cycloaddition of Phosphaalkene to an Arene Ring

Liu Leo Liu; Jiliang Zhou; Levy L Cao; Youngsuk Kim; Douglas W Stephan

doi:10.1021/jacs.9b03721

Reversible Intramolecular Cycloaddition of Phosphaalkene to an Arene Ring

J Am Chem Soc. 2019 May 22;141(20):8083-8087. doi: 10.1021/jacs.9b03721. Epub 2019 May 9.

Authors

Liu Leo Liu¹, Jiliang Zhou¹, Levy L Cao¹, Youngsuk Kim^{1

2}, Douglas W Stephan¹

Affiliations

¹ Department of Chemistry , University of Toronto , 80 St. George Street , Toronto , Ontario M5S 3H6 , Canada.
² Department of Chemistry , Pohang University of Science and Technology , Pohang 37673 , Republic of Korea.

PMID: 31055918
DOI: 10.1021/jacs.9b03721

Abstract

The phosphepinium cation 1 is deprotonated by base generating a phosphaalkene that undergoes cycloaddition to the N-bound aromatic ring affording the 2-phosphabicyclo[2.2.2]octa-5,7-diene 2. The analogous deprotonation reaction of the less bulky phosphepinium cation 3 affords a reversible equilibrium between the phosphaalkene 4 and the corresponding cycloaddition product 5. This latter observation represents the first reversible cycloaddition of a main group multiply bonded species with an arene ring. The bicyclic species 2 was also shown to be oxidized or alkylated in reactions with S₈ and MeOTf, affording 6 and 7, respectively. This finding and its implications for related cycloadditions of other main group multiply bonded species are considered computationally.