Imine photoalkylations. Papaverine, phenanthridine, and a general mechanism

Biosynthesis of Isonorargemonine, Eschscholtzidine and 4-Hydroxyeschscholtzidine inThalictrum minus

“…The data obtained indicate that reticuline (7) is incorporated in 1, 2, and 3, supporting the biogenetic hypothesis (12)(13)(14) for the role of reticuline (7) as a precursor of the pavine alkaloids. It is proposed that the formation of the pavine skeleton occurs through the intermediate iminium ion 8 followed by oxidative cyclization.…”

“…On the basis of the isolation of the 1-benzylisoquinoline alkaloid (+)-reticuline (7), together with the pavirie alkaloids (-)bisnorargemonine, (-)-norargemonine and (-)-argemonine from Argemone hispida Gray (Papaveraceae), and from their structural relationships, it appears that the pavine alkaloids are biosynthesized from the 1-benzylisoquinoline system (12)(13)(14). Reticuline (7), found in Thalictrum minus spp.…”

Simple and Clean Photo-induced Methylation of Heteroarenes with MeOH

“…In addition to MacMillan's photo-redox protocol, the use of alcohols as the alkylation regents without photo-redox catalysts under UV light irradiation has also been discussed before. [35][36][37][38][39][40][41] However, the yields were low in most of these earlier reports. Intrigued by these precedents, we report on a high-yielding protocol for heteroarene methylation using MeOH as both the solvent and the methyl source without external catalysts.…”

“…Although there are a few early examples in which the methylation product (16) from heteroarene (13) was observed, they lack some efficiency or substrate scope (Scheme 2A). [35][36][37][38]43 Mechanistically, we proposed that the generation of the hydroxymethyl radical 15 (,CH 2 OH) is the rate-limiting step. Thus, the methylation product might predominate if a more efficient pathway for generating the hydroxymethyl radical 15 (,CH 2 OH) is identified.…”

“…It has been proposed that a photo-induced electron-transfer process occurs from MeOH to the heteroarenes under UV irradiation. 35 To obtain more insight into this process, we compared the fluorescence spectra under different conditions both with and without acid. In the absence of acid, 2-methylquinoline exhibited a 4-fold weaker fluorescence intensity than that with acid ( Figures 2B and 2C).…”