Cyclization–endoperoxidation cascade reactions of dienes mediated by a pyrylium photoredox catalyst

Abstract

SummaryTriarylpyrylium salts were employed as single electron photooxidants to catalyze a cyclization–endoperoxidation cascade of dienes. The transformation is presumed to proceed via the intermediacy of diene cation radicals. The nature of the diene component was investigated in this context to determine the structural requirements necessary for successful reactivity. Several unique endoperoxide structures were synthesized in yields up to 79%.

Light on Unsaturated Hydrocarbons – “Gotta Heterofunctionalize Them All”

“…[58] To expand the scope of this reaction, the Nicewicz group developed new conditions based on those of Yoon and Miyashi [59] and aimed to use higher-oxidation-potential olefins through the use of organic photocatalysts (Scheme 42). [57] The mechanism proposed by the authors is similar to that proposed by Yoon on the basis of the results obtained by Miyashi. Nonetheless, the Nicewicz group performed DFT calculations, and the results suggested the formation of a distonic radical cation.…”

“…Nicewicz and colleagues later detailed this step on the basis of the formation enthalpy along with spin-density calculations. [57] Indeed, they suggest the effective formation of the distonic radical cation species 204, which is intercepted by O 2 to form 205. This intermediate is then reduced by 1 equiv.…”

“…Nicewicz and colleagues later detailed this step on the basis of the formation enthalpy along with spin-density calculations. [57] synthetic methods in a more controlled fashion. Indeed, the authors did not observe any production of superoxide nor any oxidative cleavage products and obtained the desired compounds in higher yields than those for the known UV conditions.…”

Visible‐Light Photoredox Catalysis Enables the Biomimetic Synthesis of Nyingchinoids A, B, and D, and Rasumatranin D

“…More recently, the scope of the aerobic [2+2+2] cycloaddition was significantly extended by Yoon and co‐workers to include less electron‐rich bis(styrene) substrates using Ru(bpz) 3 2+ as an efficient photocatalyst . Most recently, and most relevantly to this work, Gesmundo and Nicewicz showed that the use of triarylpyrylium salts as organic photocatalysts allowed the aerobic [2+2+2] cycloaddition of dienes bearing one styrene and one aliphatic alkene (Scheme ) …”

Visible‐Light Photoredox Catalysis Enables the Biomimetic Synthesis of Nyingchinoids A, B, and D, and Rasumatranin D

“…[12] Most recently,a nd most relevantly to this work, Gesmundo and Nicewicz showed that the use of triarylpyrylium salts as organic photocatalysts allowed the aerobic [2+ +2+ +2] cycloaddition of dienes bearing one styrene and one aliphatic alkene (Scheme 2). [13] Our biomimetic synthesis of nyingchinoids A, B, and Dis outlined in Scheme 3. Racemic chromene 4 was first synthesised in one step by condensation of orcinol with citral according to ak nown procedure.…”