Photorearrangement of α-Azoxy Ketones and Triplet Sensitization of Azoxy Compounds

Abstract

[reaction: see text] Although some aspects of azoxy group radical chemistry have been investigated, unhindered alpha-azoxy radicals remain poorly understood. Here we report the generation of alpha-azoxy radicals under mild conditions by irradiation of alpha-azoxy ketones 4a,b. These compounds undergo alpha-cleavage to yield radicals 5a,b, whose oxygen atom then recombines with benzoyl radicals to produce presumed intermediate 15. Formal Claisen rearrangement gives alpha-benzoyloxyazo compounds 8a,b, which are themselves photolabile, leading to both radical and ionic decomposition. The ESR spectrum of 5a was simulated to extract the isotropic hyperfine splitting constants, which showed its resonance stabilization energy to be exceptionally large. Azoxy compounds have been found for the first time to be good quenchers of triplet excited acetophenone, the main sensitized photoreaction of 7Z in benzene being deoxygenation. While this reaction has been reported previously, it was always in hydrogen atom donating solvents, where chemical sensitization occurred. The principal direct irradiation product of 4bZ and model azoxyalkane 7Z is the E isomer, whose thermal reversion to Z is much faster than that of previously studied analogues.

Maniwamycins: new quorum-sensing inhibitors against Chromobacterium violaceum CV026 were isolated from Streptomyces sp. TOHO-M025

“…24 In addition, the 15 N chemical shifts of two nitrogen atoms included in the azoxy group indicated this position. 25 Moreover, the syn-anti configurations of the azoxy moieties in all isolated maniwamycins in this paper were determined to be the Z-form. In a previous report, 15 N chemical shifts of two nitrogen atoms with an anti-configuration were higher field than those in a syn-configuration.…”

“…In a previous report, 15 N chemical shifts of two nitrogen atoms with an anti-configuration were higher field than those in a syn-configuration. 25 All reported compounds of actinomycete origin have Z-form azoxy moieties. 18 Maniwamycin B has anti-C. albicans IFM40001 activity at a concentration of 50 μg ml − 1 , 15 but the compounds we isolated in this study had no effect on Candida.…”