Synthesis of C2-Carbonyl Indoles via Visible Light-Induced Oxidative Cleavage of an Aminomethylene Group

A strategy for photochemical oxidative cleavage of the aminomethylene group at the C2 position of indole was developed to synthesize C2-carbonyl indoles. The reaction was initiated by the photochemical oxidation of N1, followed by a water-assisted concerted H-shift by abstracting hydrogen from aminomethylene. Bromopyridine was discovered to play dual roles as an oxidant for the regeneration of photocatalysts and as an accelerant for the single-electron transfer process

Curtius-like Rearrangement of an Iron–Nitrenoid Complex and Application in Biomimetic Synthesis of Bisindolylmethanes

A Curtius-like rearrangement of hydroxamates to isocyanates was discovered. This reaction was initiated from an iron­(II)–nitrenoid complex, which was generated by the iron­(II)-catalyzed cleavage of N–O bonds of functionalized hydroxamates. To demonstrate the efficiency of this new Curtius-like rearrangement in synthetic chemistry, a biomimetic strategy for the one-pot preparation of bisindolylmethanes was developed

Synthesis of Pyrrolo[2,3‑<i>b</i>]indole via Iodine(III)-Mediated Intramolecular Annulation

New synthetic procedures for the pyrrolo[2,3-<i>b</i>]indole skeleton have been developed via intramolecular annulation of indole derivatives under iodine(III). A series of indole derivatives with different protecting groups or substitutions were explored to facilitate the corresponding pyrrolo[2,3-<i>b</i>]indole compounds in excellent yields

4,5-Cis Unsaturated α‑GalCer Analogues Distinctly Lead to CD1d-Mediated Th1-Biased NKT Cell Responses

The total synthesis of 4,5-cis unsaturated α-GalCer analogues was achieved, and their immune-response altering activity was assessed <i>in vitro</i> as well as <i>in vivo</i> in mice. Using glycosyl iodide as a glycosyl donor, construction of the sphingosine unit was shortened by four steps and single α-stereoselectivity was achieved in good yield (67%). With regard to the therapeutic use of α-GalCer, the novel analogues (<b>1b</b> and <b>1c</b>) distinctly induced a Th1-biased cytokine response, avoiding induction of a contradictory response and overstimulation

Total Synthesis of (+)-Chimonanthine, (+)-Folicanthine, and (−)-Calycanthine

Facile, straightforward, and asymmetric total syntheses of (+)-chimonanthine (<b>1</b>), (+)-folicanthine (<b>2</b>), and (−)-calycanthine (<b>3</b>) were accomplished in four to five steps from commercially available tryptamine. The synthesis features copper-mediated asymmetric cyclodimerization of chiral tryptamine derivative, which established a new entry into constructing the sterically hindered vicinal quaternary stereogenic carbon centers of dimeric hexahydropyrroloindole alkaloids in one procedure. An unprecedented base-induced isomerization from the chimonanthine skeleton to the calycanthine skeleton was observed and facilitated the synthesis of (−)-calycanthine (<b>3</b>)

Copper-Catalyzed Radical Cyclization To Access 3‑Hydroxypyrroloindoline: Biomimetic Synthesis of Protubonine A

An unprecedented copper-catalyzed intramolecular radical cyclization was developed for the synthesis of 3-hydroxypyrroloindoline skeletons in excellent yields. The 3-hydroxyl group was introduced by trapping the radical intermediate with molecular oxygen or TEMPO. This process represents a unique radical oxidation pathway for tryptamine/tryptophan derivatives and allows a rapid biomimetic synthesis of natural product protubonine A

Biomimetic Synthesis of Moschamine-Related Indole Alkaloids via Iron-Catalyzed Selectively Oxidative Radical Coupling

An iron-catalyzed oxidative radical coupling reaction was developed to selectively construct indolofuran or bisphenolic indole cores, which exist in two types of moschamine-related indole alkaloids. Both (+)-decursivine and 4,4″-bis­(<i>N</i>-feruloyl)­serotonin were biomimetically synthesized by using coupling reactions. The proposed reassignment of the structure of montamine as 4,4″-bis­(<i>N</i>-feruloyl)­serotonin was excluded

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

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

Copper-Mediated Dimerization to Access 3a,3a′-Bis­pyrrolidino­indoline: Diastereoselective Synthesis of (+)-WIN 64821 and (−)-Ditrypto­phenaline

A copper-mediated cyclization and dimerization of tryptamine or tryptophan was developed to generate a <i>C</i>₂-symmetry C₃(sp³)–C₃(sp³) bridge with two contiguous stereogenic quaternary carbons in one step. Impressively, the ratio between exo and endo cyclization products varies when different protecting groups of Nb are utilized. This dimerization reaction could be conducted in gram scale. With this dimerization method, both endocyclo­tryptophan (+)-WIN 64821 and exocyclo­tryptophan (−)-ditrypto­phenaline were synthesized in 5 steps