Heterocycles with Two or Three Heteroatoms

Austin and Ridd712 have described an interesting ring-closing transformation of 

1- ethyl-2-nitrobenzene to 3-methylbenzo[c]isoxazole in triflic acid. On the basis of deuterium labeling and the large substituent effect observed (the reaction of 1 -methyl- 

2- nitrobenzene is extremely slow), the mechanism shown in Eq. (5.261) including a hydride transfer from the benzyl carbon to one of the oxygens of the protonated nitro group as the rate-determining step has been proposed. 

Shudo and co-workers183 found that nitroalkenes react with benzene in triflic acid to yield AHA, 2-benzoxazines in a two-step reaction the 9, 9-diprotonated 

Deuterium labeling studies indicated that the electrocyclization mechanism necessitating the removal of a benzylic hydrogen, suggested earlier by Shudo and co-workers,183 is not operative here. Instead, experimental observations indicate the 

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