698349-15-4Relevant academic research and scientific papers
New 1,3-dihydroazepin-2-one derivatives by [3,3]-sigmatropic rearrangement of suitably substituted 2-alkenylcyclopropyl isocyanates
Reissig, Hans-Ulrich,Boettcher, Gesine,Zimmer, Reinhold
, p. 166 - 176 (2004)
The 2-siloxysubstituted 2-alkenylcyclopropanecarboxylic acids 10-14 were converted into the corresponding carbonyl azides by treatment with DPPA (diphenyl phosphorazidate) and triethylamine. On heating to 80°C these intermediates smoothly furnished azepinone derivatives 19-25 in moderate to good overall yields, which are the result of a sequence of Curtius reaction to cyclopropylisocyanates, [3,3]-sigmatropic rearrangement, and a final proton shift. The primary products may undergo desilylation (to afford azepin-2,5-diones such as 23) or double bond migration (to compound 25). Cyclopropanecarboxylic acids cis-32, cis-34, and cis-35, which bear no 2-siloxy group, similarly provided azepinone derivatives 36-38 in good yields. No influence of the 2-siloxy substituent on the reaction course and rates could be observed in these qualitative studies, which was confirmed by DFT calculations with model compounds 39-42 showing similar reaction barriers for rearrangements of cyclopropylisocyanates with or without a 2-hydroxy group.
