Photo-oxidation and Thermal Oxidations of Triptycene Thiols by Aryl Chalcogen Oxides

Photochemistry of N-aryl and N-alkyl dibenzothiophene sulfoximines

N-phenyl dibenzothiophene sulfoximine has been demonstrated to produce phenyl nitrene and dibenzothiophene S-oxide upon irradiation with UV-A light, and dibenzothiophene S-oxide upon further irradiation releases triplet atomic oxygen. Thus, N-phenyl dibenzothiophene sulfoximine exhibits a rare dual-release capability in its photochemistry. In this work, N-substituted dibenzothiophene sulfoximine derivatives are irradiated with UV-A light to compare their photochemistry and quantum yield of dibenzothiophene S-oxide production with that of N-phenyl dibenzothiophene sulfoximine. Both N-aryl and N-alkyl derivatives of dibenzothiophene sulfoximine are examined to observe their effects on the quantum yield of the photolysis reaction. Adding electron withdrawing N-aryl substituents is shown to increase the quantum yield of dibenzothiophene S-oxide production, while adding electron donating N-aryl substituents is shown to decrease the quantum yield. The quantum yield was slightly lowered or not increased by most N-alkyl substituents. Furthermore, the quantum yield was not augmented by branching and steric hindrance effects associated with the N-alkyl substituents. These results suggest that electronic modulation of the sulfoximine bonds affects the observed photolysis reaction.

Two-step Two-intermediate Photorelease Bolm-McCulla Reaction: Dual Release of Nitrene and Atomic Oxygen Reactive Intermediates

This article is a highlight of the paper by Isor et al. in this issue of Photochemistry and Photobiology. It describes the photolysis of a dibenzothiophene sulfoximine (bearing N-phenyl imino and S-oxide groups) to produce two reactive intermediates in tandem. The sulfoximine undergoes a S-N and S-O photocleavage to release phenyl nitrene and atomic oxygen [O(³ P)]. The phenyl nitrene dimerizes to azobenzene or is trapped by diethylamine to reach an azepine. From there, atomic oxygen arises in a secondary photolysis of dibenzothiophene sulfoxide. A computational analysis also reveals that the S-N bond is labile for initial nitrene release, with the secondary release of atomic oxygen by S-O cleavage. Whether future sulfoximine scaffolds can produce the reverse order release of O(³ P) then nitrene, or release both simultaneously, is yet to be established. Nonetheless, molecules with dual-intermediate release, such as coupled photoaffinity labeling and cellular oxidation, are worth pursuing.