Redox-Neutral Intramolecular Dearomative Spirocyclization of Phenols Induced by Visible Light.

Described herein is a redox-neutral intramolecular dearomative spirocyclization induced by visible light. The photochemical cyclization was catalyzed by a phenolate anion-derived photocatalyst and delivered the spirocyclohexadienone. Mechanistic experiments revealed that the aryl halide was reduced to aryl radical via the single-electron transfer (SET) process under visible light irradiation. The electrophilic addition of an aryl radical with the phenolate anion moiety gave a radical anion intermediate, which recycled the photocatalyst by a second SET process.

Chichibabin pyridinium synthesis via oxidative decarboxylation of photoexcited α-enamine acids.

A visible light-induced decarboxylative Chichibabin pyridinium synthesis between α-amino acids and aldehydes was developed. When the in situ generated α-enamine acids were photoexcited, they were oxidized by aerobic oxygen to give radical cation species. After decarboxylation and further oxidation, the generated iminium undergoes Chichibabin cyclization to afford pyridiniums. This photochemical protocol enables the synthesis of various tetra-substituted pyridiniums and related natural products in one-step.

Photochemical α-carboxyalkylation of tryptophols and tryptamines via C-H functionalization.

A process for the α-carboxyalkylation of tryptophols and tryptamines by the functionalization of C-H bonds under visible light irradiation has been developed. The photochemical strategy activated the C-Br bonds of α-bromo-alkylcarboxylic esters to provide carbon-centered radicals under the catalysis of Ir(iii) photocatalyst and coupled with indole derivatives. This methodology displayed wide functional group tolerance and excellent regioselectivity, and was applied to the late-stage functionalization and preparation of indole-containing hybrids.

Enantioselective Synthesis of Spiroindolines via Cascade Isomerization/Spirocyclization/Dearomatization Reaction.

The spiroindoline skeleton featured with 2,7-diazaspiro[4.4]nonane exists in various structurally intricate and biologically active monoterpene indole alkaloids. A catalytic asymmetric cascade enamine isomerization/spirocyclization/dearomatization succession to construct the spiroindoline was developed, which employed the indolyl dihydropyridine as a substrate under catalysis of the chiral phosphoric acid. This cascade reaction provided various spiroindolines in both diastereoselective and enantionselective fashions.