Buchner Reaction/Azirine Modification Approach Toward Cycloheptatriene Containing Nitrogen Heterocyclic Scaffolds

The reaction conditions for the Buchner reaction of 2-(diazoacetyl)-2H-azirines with benzene leading to 2-(cyclohepta-2,4,6-trien-1-yl)-2H-azirines have been found. The azirine fragment of these compounds was subsequently used to prepare 5-(cyclo- hepta-2,4,6-trien-1-yl)isoxazoles and alpha-(cyclohepta-2,4,6-triene-1-ylcarbonyl)-1H-pyrroles. NMR and DFT calculations showed that the cycloheptatriene-norcaradiene valence isomerization in the corresponding moieties of synthesized azirines, isoxazoles, and pyrroles is very fast at room temperature. Cycloheptatriene valence isomer predominates in azirines and pyrroles, while 5 (cycloheptatrienyl)isoxazoles exist in a pure cycloheptatriene form at 25 degrees C in chloroform solution. In accordance with the X-ray analysis, two of the synthesized pyrroles crystallized as norcaradiene isomers from a solution of equilibrium mixture of valence isomers. Reductive isoxazole ring opening using the Mo(CO)(6)/H2O reductive system afforded (Z)-3-amino-3-aryl-1-(cyclohepta-2,4,6-trien-1-yl)prop-2-en-1-ones, which are pure cycloheptatriene isomers. alpha-(Cycloheptatrieneylcarbonyl)-1H-pyrroles were transformed into the alpha-(benzylcarbonyl)-1H-pyrroles under cooperative TFA/Rh,(TFA), catalysis.

Automated summary

The Buchner reaction conditions for synthesizing a range of cyclohepta-1-yl azirines and their derivatives have been discovered, leading to the formation of cyclohepta-2,4,6-trien-1-yl isoxazoles and alpha-(cyclohepta-2,4,6-triene-1-ylcarbonyl)-1H-pyrroles. Research shows that these compounds undergo rapid cycloheptatriene-norcaradiene valence isomerization at room temperature.