Stepwise Photoreduction of (iso)Alloxazine N-Oxides in the Presence of 1,4-Cyclohexadiene

Abstract

N -O xidation, Steric hindrance, Photoreduction. A lloxazine N -oxideThe direct syn th esis o f (iso)alloxazine N -ox id es using trifluoroperacetic acid in situ is reinvestigated, show ing sen sitiv ity tow ards steric (peri) hindrance. The photoreduction of these N -oxid es in th e presence o f 1.4-cyclohexadiene yields the parent (iso)alloxazine. The reduction o f the N -oxid es b y in itia lly form ed dihydro (iso)alloxazine is ruled out for the photoreduction.Continuing our investigations of the photoreductions of N-heterocyclic compounds in the pres ence of 1,4-cyclohexadiene1-2 wre examined the reaction of this compound with the photoactivated N-oxides (1-4).In contrast to the literature4-5 wre found th a t the compounds lb and 3b could not be synthesized following the experimental procedures given: The direct oxidation of 1,3-dimethyl alloxazine does not yield lb but 2b as could be shown by tic comparison with authentic m aterial3, wiiereas in the case of the N(l)-unsubstituted 3-methyl alloxazine the Noxidation proceeds in position 10 yielding l a 4. Similarly the N(10)-oxidation of 2 b, w'hich is claimed to yield 3 b5, is not possible due to steric hindrance of the N(l)-m ethyl group of 2 b. The same Requests for reprints should be sent to W .-R . K n a p p e , Fachbereich B iologie der U n iversität, D -7750 Konstanz, P ostfach 733.