New 1,3-dihydroazepin-2-one derivatives by [3,3]-sigmatropic rearrangement of suitably substituted 2-alkenylcyclopropyl isocyanates

Abstract

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.Key words: vinyl cyclopropanes, carbonylazides, [3.3]-sigmatropic rearrangements, azepinones.

Continuous flow photolysis of aryl azides: Preparation of 3H-azepinones

“…Performing the reaction in the presence of water typically affords 3 H -azepinone 7 [ 31 – 34 ], a moiety present in natural products [ 35 – 36 ] and in azepinone-derived pharmaceuticals [ 37 – 38 ]. Despite the importance of these 7-membered nitrogen-containing heterocycles, there remain few methods for their preparation [ 39 – 44 ]. Overall, aryl azides, which are simple to prepare from the corresponding aniline derivative, are convenient precursors for the synthesis of azepine derivatives.…”

Synthesis of (Z)‐Trisubstituted Olefins by Decarboxylative Grob‐Type Fragmentations: Epothilone D, Discodermolide, and Peloruside A

“…All attempts to convert the ester into the carboxylate either by using various hydroxides, KOTMS or the Krapcho protocol failed. [22,23] However, after reducing the ester to the aldehyde, fragmentation gave olefin 71 in excellent yield. Notwithstandingly, the lactone route appears more reliable, as inversion of the b-OH and regioselective protection of the d-OH position might be problematic in acyclic molecules.…”

Direct synthesis of new soluble and thermally stable poly(urethane‐imide)s from an imide ring‐containing dicarboxylic acid using diphenylphosphoryl azide

“…Thereafter, in 1991, various kinds of polyurethanes were prepared by Nishi et al through the reaction of a hydroxyl group with the isocyanate group that was formed by Curtius rearrangement of the carbonyl azide precursor 7. In general, the most carbonyl azides are readily converted to corresponding isocyanates, which react in situ with hydroxylic compounds to form urethanes 8, 9…”