INSERTION OF NITROGEN-OXIDE AND NITROSONIUM ION INTO THE CYCLOPROPANE RING - A NEW ROUTE TO 2-ISOXAZOLINES AND ITS MECHANISTIC STUDIES

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.