Visible-light promoted allylation of N-substituted tetrahydroisoquinoline using riboflavin tetra-acetate as photocatalyst

Riboflavin Photocatalyzed Dearomative Spiro-Etherification of Naphthols

“…Next, the mechanism of the dearomatization reaction was investigated. During the control experiments it was observed that the starting material (1a) remained unreacted in the absence of RFTA, O 2 atmosphere and blue light (Table 1, entry 22,23,24), which indicates that the reaction proceeds via the single electron transfer mechanism. Further, in the presence of 2 equivalents of TEMPO in the reaction mixture, no spiroether (2a) was obtained, and the starting material (1a) completely decomposed.…”

“…It was found that HCOOH is required for successful formation of the spiroether ( 2a ) (Table , entry 16). The presence of acid modifies the redox property of RFTA by protonation. , The reduction and oxidation potential of RFTA and 2-naphthol ( 1a ) were determined using cyclic voltammetry in the presence and absence of HCOOH in acetonitrile.…”

“…We approached this challenge with visible light photocatalysis, as this delivered a straight forward environmentally benign catalytic achievement of phenol dearomatization. Riboflavin tetraacetate (RFTA) catalyzes the aerobic photooxidation of benzyl alcohols to aldehydes, benzyl amines to aldehydes, sulfides to sulfoxides, allylation of N-substituted tetrahydroisoquinoline, photooxidative coupling of aldehydes with amines, cyanation of aliphatic carboxylic acids, esterification of carboxylic acids with alcohols, and the C–H bond oxidation of alkyl benzenes to the corresponding aldehydes . Some particularly intriguing applications of RFTA are the photocatalytic synthesis of benzo-3,4-coumarins directly from biaryl carboxylic acids, photooxidation of aldehydes to methyl esters, photocatalytic synthesis of benzothiazoles from thiobenzanilides, and nitration of protected anilines .…”