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

Two different C-13-labeled 7-trifluoromethyl-N-1,N-10-ethyleneisoalloxazini um chlorides were utilized to examine the mechanism of amine dehydrogenatio n. H-1 NMR studies in CD3CN (C-13 NMR in DMSO-d(6)), as confirmed using N-1 5-labeled benzylamine, indicate that primary and secondary amines add to gi ve tetrahedral C-10a adducts that persist for hours at 25 degreesC. Upon he ating, the C-10a amine adducts partition between rearrangement to C-4a spir ohydantoin amidines, and, in the case of benzylic amines, beta -elimination to give reduced flavin and imine dehydrogenation product. A C-10a tetrahed ral hydroxy adduct, generated under basic conditions when water was present , was also confirmed by H-1/C-13 NMR. (C) 2001 Elsevier Science Ltd. All ri ghts reserved.