Insertion of nitrogen oxide and nitrosonium ion into the cyclopropane ring: a new route to 2-isoxazolines and its mechanistic studies
摘要:
The 9,10-dicyanoanthracene (DCA)-sensitized photoreaction of 1,2-diarylcyclopropanes 1a-d in nitrogen oxide (NO)-saturated CH3CN afforded 3,5-diaryl-2-isoxazolines 2a-d in excellent yields. The reaction of 1a-d with NOBF4 or with a mixture of NO and O2 in CH3CN also afforded 2a-d or 2a-b. These reactions proceed via the attack of NO on the radical cation of 1, which is formed by electron transfer from 1 to 1DCA* or NO+. The reaction of 1-alkyl-2-arylcyclopropanes with NOBF4 afforded mixtures of 3-alkyl-5-aryl-2-isoxazolines and 4-alkyl-5-aryl-2-isoxazolines via the direct attack of NO+ on the cyclopropane rings. The reaction of 1,1,2,2-tetraphenylcyclopropane with NOBF4 afforded 2,3,5,5-tetraphenyl-2-isoxazolinium tetrafluoroborate via the migration of the phenyl group to nitrogen.
9,10-Dicyanoanthracene-sensitized photoreaction of electron-rich 1,2-diarylcyclopropanes with NO in acetonitrile afforded 3,5-diaryl-2-isoxazolines in good yields. The cyclopropanes bearing different aryl-substituents gave a mixture of two isomeric 2-isoxazolines. Mechanistic features of this reaction are described.
The 9,10-dicyanoanthracene (DCA)-sensitized photoreaction of 1,2-diarylcyclopropanes 1a-d in nitrogen oxide (NO)-saturated CH3CN afforded 3,5-diaryl-2-isoxazolines 2a-d in excellent yields. The reaction of 1a-d with NOBF4 or with a mixture of NO and O2 in CH3CN also afforded 2a-d or 2a-b. These reactions proceed via the attack of NO on the radical cation of 1, which is formed by electron transfer from 1 to 1DCA* or NO+. The reaction of 1-alkyl-2-arylcyclopropanes with NOBF4 afforded mixtures of 3-alkyl-5-aryl-2-isoxazolines and 4-alkyl-5-aryl-2-isoxazolines via the direct attack of NO+ on the cyclopropane rings. The reaction of 1,1,2,2-tetraphenylcyclopropane with NOBF4 afforded 2,3,5,5-tetraphenyl-2-isoxazolinium tetrafluoroborate via the migration of the phenyl group to nitrogen.