Catalytic opening of the diaziridine fragment in 6-aryl-1,5-diazabicyclo[3.1.0]hexanes

Treatment of 6-aryl-1,5-diazabicyclo3.1.0]hexanes with Lewis acids BF₃·Et₂O or In(OTf)₃] promotes opening of the diaziridine ring, followed by formation of 1,3-dipolar cycloaddition products with N-arylmaleimides. The conversion of the initial diaziridine depends on the nature of the 6-aryl group. Diazabicyclohexanes with donor substituents react quantitatively to give (in the absence of dipolarophiles) the corresponding azomethine imine dimers, 1,2,4,5-tetrazine derivatives. The conversion of diazabicyclohexanes having acceptor substituents is poor; simultaneously, the fraction of the hydrolysis products increases. The stereoselectivity in the 1,3-dipolar cycloaddition, i.e. the ratio of the cis-and trans-adducts, depends on the catalyst and solvent. Azomethine imine dimers react with N-arylmaleimides in the presence of indium(III) trifluoromethanesulfonate to give the same 1,3-dipolar cycloaddition products as those obtained from parent 1,5-diazabicyclohexanes.