Cycloaddition of 1-Azirines with Cyclopentadienones. Formation of 2H- and 3H-Azepines, and Mechanistic Interpretation

Alfred Hassner, David J. Anderson

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26 Scopus citations

Abstract

Cyclopentadienones 1 and 1-azirines 2 react in refluxing toluene to afford 3H-azepines 3 directly, with loss of CO. Azirines 2 react similarly with 1,3-diphenylinden-2-one (16) and phencyclone (17) to give 2H-azepines 18 and 19. The phenanthro-2/í-azepines 19 rearrange under basic or thermolytic conditions to the more stable 3H isomers with the ring proton at the 9 position of the phenanthrene nucleus. Analogous cycloadditions of 16 and 17 with 1,2,3-triphenylcyclopropene (22) lead to cycloheptatrienes and exo bridging carbonyl compounds. The mechanism of azepine formation is rationalized in terms of an erado-2-azatricyclo[3.2.1.02,4]oct-6-en-8-one intermediate (13) which extrudes CO with disrotatory ring opening of the aziridine C-N bond, to afford primarily 2Hazepines which may or may not then rearrange to the 3H isomers. Analysis of the nmr spectra, with particular attention to the conformational preference of the azepine ring, is also recorded.

Original languageEnglish
Pages (from-to)3070-3076
Number of pages7
JournalJournal of Organic Chemistry
Volume39
Issue number21
DOIs
StatePublished - 1 Oct 1974
Externally publishedYes

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