1,1-Dihalo-2-benzycyclopropanes in reaction with nitrous acid

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

“…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.…”

Three-Component Heterocyclization of gem-Bromofluorocyclopropanes with NOBF4: Access to 4-Fluoropyrimidine N-Oxides

“…[8][9][10][11]34,35 Two mechanistic rationales could be therefore postulated. The first step of the ionic pathway involves the electrophilic attack of NO + and the opening of the three-membered ring (path A, Scheme 4) resulting in the formation of the intermediate II.…”

“…Such result is in agreement with the literature data for benzyl-substituted dichlorocyclopropanes. 10 On the contrary, aryl-substituted compounds 6d−g reacted with NOBF 4 rapidly at room temperature giving the corresponding 6-aryl-substituted pyrimidine N-oxides 7d−g. Markedly, these reactions proceeded with high regioselectivity, and no traces of 5-aryl-substituted isomers were observed in the reaction mixture.…”

“…Both ionic and radical pathways are proposed in the literature for the reaction of cyclopropanes with nitrosonium cation which may act as an electrophilic nitrosylation reagent and also as a strong one-electron oxidant. [8][9][10][11]34,35 Two mechanistic rationales could be therefore postulated. The first step of the ionic pathway involves the electrophilic attack of NO + According to the literature data, 8−11 the most likely scenario for the subsequent step is the intramolecular cyclization of carbocation II, yielding the isoxazole moiety shown in Scheme 5.…”

“…Reactions between gem -dihalogenocyclopropanes and various sources of the nitrosonium cation are known to be a straightforward and effective way to obtain 5-halogeno-substituted isoxazoles. − We note that the prior nitrosylation studies were limited to studying gem -dichloro- and dibromocyclopropanes in the reaction, and no attempts were made to utilize fluorine-containing cyclopropanes as a starting material. At the same time, 1-bromo-1-fluorocyclopropanes are readily available via cycloadditions of bromofluorocarbene to CC double bonds under relatively mild conditions − and can be subsequently used for heterocyclizations under the conditions promoting the opening of the three-membered ring.…”