Nitrile oxides olefin regioselectivity

On the other hand, reactions of nitrile oxides with 1,2-disubstituted olefins are slower and regioselectivity usually was not so high. For example, benzonitrile oxides, obtained from the corresponding chlorooximes 167, undergo 1,3-dipolar cycloaddition reaction with methyl cinnamate to produce the 5-phenyl 168 and 4-phenyl 169 regioisomers in approximately an 80 20 ratio °. However, use of A,iV-diethylcinnamamide as the dipolarophile... 

Cycloaddition of a nitrile oxide to a substituted olefin can lead to two regio-isomers, the 4- and/or 5-substituted 2-isoxazoline. Reactions of monosubstituted alkenes give the 5-substituted isomers 18 with almost complete regioselectivity (10,15,30,109). This result is also supported by ab initio and FMO calculations (114,119). Change of substituents in the dipole has little effect on the regioselectivity of such reactions when monosubstituted alkenes are used (Table 6.4). 

---