Oxidation of N-Acylindoles by Dimethyldioxirane and Singlet Oxygen: Substituent Effects on Thermally Persistent Indole Epoxides and Dioxetanes

Article abstract of DOI:10.1021/jo00089a016

Photooxygenation of the N-acylindoles 1a-d afforded the labile indole dioxetanes 2 and the relatively stable allylic hydroperoxides 3.The dioxetanes 2a,c,d were sufficiently stable for isolation and spectral characterization.Additionally, they were characterized by chemical transformations, namely reduction to the indole epoxides 5 by dimethyl sulfide, acid-catalyzed rearrangement to allylic hydroperoxides 3c,d, and thermolysis to the cleavage products 4.Oxidation of the N-acylindoles 1 with dimethyldioxirane afforded the epoxides 5, which were characterized on the basis of their spectral data and chemical transformations to the 2-indolinones 6 and 2-methyleneindoline 7.These decomposition products (except 7e) were fully characterized.The stability of the epoxides 5 depended on the substitution type, i.e., the carbazole epoxide 5c decomposed already at temperatures above ca. -50 deg C, whereas the cyclopentindole epoxide 5b was stable at 20 deg C for days.The latter was unequivocally characterized by X-ray analysis.