Arylnitrile oxides, 1,3-dipolar cycloaddition

Benzocyclobutene, when generated by oxidation of its iron tricarbonyl complex, can function as the dipolarophile in 1,3-dipolar cycloaddition reactions with arylnitrile oxides (Scheme 113).177 Unfortunately the synthetic versatility of this type of process is limited because of the unreactivity of other 1,3-dipolar species such as phenyl azide, benzonitrile N-phenylimide, and a-(p-tolyl)benzylidenamine N-oxide.177... 

Cycloaddition. 4-Methylene-4,5-dihydroisoxazoles (174) are good dipolarophiles towards a variety of 1,3-dipoles (e.g., arylnitrile oxide (177)) to form a spiral compound (178), which is not easily accessible by other routes. The resulted 1,3-dipolar cycloaddition product (178) is regio- and stereoselective <95SL1208>. The exocyclic double bond of (174) is sluggish towards the diene systems, but with the activated diene, 2,5-dimethyl-3,4-diphenyl-2,4-cyclopoentadienone (179) yielded the Diels-Alder product (180) (Scheme 27) <95SL1208>. 

The only reported example of this kind is the 5-isoxalyl carbocyclic isoxazole 471 that was prepared by 1,3-dipolar cycloaddition of arylnitrile N-oxides with the alkene side chain of 469 (76CJC861) (Scheme 118). 

Diaz-Ortiz described the microwave-induced 1,3-dipolar cycloadditions of mesi-tonitrile oxide to aliphatic and aromatic nitriles under solvent-free conditions. The adducts were obtained in shorter reaction times and better yields than with classical methods [84]. By the same approach, Corsaro reported the successful cycloaddition of arylnitrile oxides to naphthalene or aromatic polycyclic dipolaro-philes under solvent-free microwave activation [85]. In the same report, the yields of bis-cycloadducts were also improved by microwave exposure [85]. 

Dihydro-l,4-diazepines will perform 1,3-dipolar cycloaddition reactions with nitrile oxides and nitrile imines but it is only the imine bonds in the diazepine that react. Thus, 2,3-dihydro-5,7-diphenyl-1-methyl-17/-1,4-diazepine (64 R = Me) only gave mono adducts (65) with arylnitrile... 

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