Cycloaddition of 1-Azirines to 1,3-Diphenylisobenzofuran and Rearrangement of the Adducts

1-Azirines 1 and 1,3-diphenylisobenzofuran (2) react smoothly and efficiently in refluxing toluene to afford the simple 1:1 adducts 3, possessing the exo configuration. Two of the adducts, 3a and 3b, were found to rearrange in the presence of neutral alumina, to give the epoxybenzo-2H-azepines 20a and 20b. Chemical reactions (water, alcohol, LiAlH₄) of the adducts 3 generally involved initial opening of the oxido bridge in a regiospecific manner. When more vigorous conditions were used, rupture of the aziridine ring usually followed.