Reaction of amines with N~1,N~(10)-ethylene-bridged flavinium salts: the first NMR spectroscopic evidence of C~(10a) tetrahedral amine adducts

摘要

Two different ~(13)C-labeled 7-trifluoromethyl-N~1,N~(10)-ethyleneisoalloxazinium chlorides were utilized to examine the mechanism of amine dehydrogenation.~1H,NMR studies in CD_3CN (~(13)C NMR in DMSO-d_6), as confirmed using ~(15)N-labeled benzylamine,indicate that primary and secondary amines add to give tetrahedral C~(10a) adducts that persist for hours at 25degC.Upon heating,the C~(10a) amine adducts partition between rearrangement to C~(4a) spirohydantoin amidines,and,in the case of benzylic amines,#beta#-elimination to give reduced flavin and imine dehydrogenation product.A C~(10a) tetrahedral hydroxy adduct,generated under basic conditions when water was present,was also confirmed by ~1H/~(13)C NMR.