A Novel NO Insertion into Cyclopropane Ring by Use of NOBF4· Formation of 2-Isoxazolines

Abstract

The reaction of 1,2-diarylcyclopropanes with NOBF4 in CH3CN gave 3,5-diaryl-2-isoxazolines in good yields. For unsymmetrically substituted cyclopropanes, the mixtures of two isomeric isoxazolines were obtained. The mechanism and regioselectivity in this NO insertion into the cyclopropane ring are described.

Reaction of esters of 2-arylcyclo-propanecarboxylic acids with nitrous acid. Synthesis of aryl-substituted 3-ethoxycarbonyl-4,5-dihydroisoxazoles and 3-ethoxycarbonylisoxazoles

“…Since the formation of a nitronium cation (NO 2 + ) required for the electrophilic nitration of aromatic ring, appears unlikely under the reaction conditions employed, we may assume that both processes in our case occur through the single-electron oxidation of substrate 2e with subsequent reaction of radical cation 5 with ON • or O 2 N • radicals. NO We should note that the proposed scheme for the conversion of ethoxycarbonylcyclopropane 2e involving the one-electron oxidation of this compound is in accord both with the scheme proposed by Ichinose et al [11] for the insertion of nitric oxide into the cyclopropane ring of 1,2-diarylcyclopropanes, whose first ionization potential permits oxidation of the starting substrates by the nitrosyl cation to the corresponding radical cations and a scheme involving nitration of arylcyclopropanes by dinitrogen tetroxide through a single-electron transfer (SET) mechanism [8]. Nitroaromatic compound 2h formed due to the complexing action of the electron-donor and electron-withdrawing substituents apparently may be comparable in their reactivity with unsubstituted 1-ethoxycarbonyl-2-phenylcyclopropane (2a), which accounts for its subsequent transformation into nitro-substituted 3-ethoxycarbonyl-4,5-dihydroisoxazole (3f) at a rate as far as we can estimate from the yields of reaction products 3e,f, only 2.5 times less than the rate of the conversion of ethoxycarbonylcyclopropane 2e.…”

“…The arylcyclopropanes studied in these transformations have been either phenylcyclopropanes [7][8][9] or benzylcyclopropanes [10] substituted in the aromatic ring or have contained only alkyl and aryl groups [11,12] or halogen atoms [13,14] as the second substituent in the cyclopropane ring. Hence, the possible series of substituted 4,5-dihydroisoxazoles and corresponding isoxazoles obtained by this method has been limited to heterocycles with nonfunctional substituents.…”

Catalytic Cyclopropanation with Iron(II) Complexes

“…Arylcyclopropanes are reactive molecules and valuable synthetic intermediates. For example, they have been used as starting materials in the synthesis of 1,3-dihalo-1,3-diarylpropanes, 1,3-dimethoxy-1,3-diarylpropanes, 3,5-diaryl-1,2-dioxolanes, 3,5-diaryl-2-isoxazolines, and cyclopropanecarboxylic acids . In addition, arylcyclopropanes also possess useful photochemical properties .…”