New approaches to ondansetron and alosetron inspire a versatile, flow photochemical method for indole synthesis

Aryl-aryl cross-coupling reactions without reagents or catalysts: photocyclization of ortho-iodoaryl ethers and related compounds via triplet aryl cation intermediates

Cyclisations of benzyl ortho-iodoaryl ethers to benzo[c]chromenes can be effected without reagents or catalysts by irradiation with UVC under flow. Reactions proceed via triplet aryl cation generation, 5-exo and 3-exo-cyclisations, and rearomatisation. They have wide scope, are easy to effect and extend to a myriad of related ring systems.

Rh(III)-Catalyzed Direct C-H Cyclization of N-Nitrosoanilines with 1,3-Dicarbonyl Compounds: A Route to Tetrahydrocarbazol-4-ones

A novel and efficient Rh(III)-catalyzed direct C-H bond tandem annulation of N-nitrosoanilines with 1,3-dicarbonyl compounds through two C-H bond cleavage was developed. This protocol provides a rapid access to a series of valuable tetrahydrocarbazol-4-ones with the feature of readily available starting materials, broad functional group tolerance, and in situ generation of carbene precursors. Importantly, some reaction products exhibited promising antiproliferative activity in cancer cell lines.

Catalytic Enantioselective 6π Photocyclization of Acrylanilides

Controlling absolute stereochemistry in catalytic photochemical reactions is generally challenging owing to high rates of background reactivity. Successful strategies broadly rely on selective excitation of the reaction substrate when associated with a chiral catalyst. Recent studies have demonstrated that chiral Lewis acid complexes can enable selective energy transfer from a photosensitizer to facilitate enantioselective triplet state reactions. Here, we apply this approach to the enantioselective catalysis of a 6π photocyclization through the design of an iridium photosensitizer optimized to undergo energy transfer to a reaction substrate only in the presence of a chiral Lewis acid complex. Among a group of iridium(III) sensitizers, enantioselectivity and yield closely correlate with photocatalyst triplet energy within a narrow window enabled by a modest reduction in substrate triplet energy upon binding a scandium/ligand complex. These results demonstrate that photocatalyst tuning offers a means to suppress background reactivity and improve enantioselectivity in photochemical reactions.

Ru(II)-Catalyzed Decarbonylative Alkylation and Annulations of Benzaldehydes with Iodonium Ylides under Chelation Assistance

A Ru(II)-catalyzed decarbonylative alkylation and annulation of salicylaldehydes and 2-aminobenzaldehydes with iodonium ylides has been developed for the synthesis of dibenzo[b,d]furans and NH-free carbazolones. The reaction proceeds smoothly under mild conditions with a low catalyst loading and a broad substrate compatibility. Notably, hydroxy and free amino groups were demonstrated to be the effective directing groups, enabling the successful aldehyde C-H bond activation and subsequent decarbonylation and annulation under the inexpensive Ru(II) catalyst.

Synthesis of Tetrahydrocarbazol-4-ones via Rh(III)-Catalyzed C-H Activation/Annulation of Arylhydrazines with Iodonium Ylides

The rhodium(III)-catalyzed C-H activation followed by intramolecular annulation reactions between arylhydrazines and iodonium ylides under suitable conditions has been described. Tetrahydrocarbazol-4-ones are readily achieved with moderate to excellent yields. The synthetic protocol features a wide range of substrates with high functional group tolerance. The gram-scale reaction and derivatization of the product demonstrate the synthetic practicality and utilization of this method.

Wavelength dependent photoextrusion and tandem photo-extrusion reactions of ninhydrin bis-acetals for the synthesis of 8-ring lactones, benzocyclobutenes and orthoanhydrides

Ninhydrin bis-acetals give access to 8-ring lactones, benzocyclo-butenes and spirocyclic orthoanhydrides through photoextrusion and tandem photoextrusion reactions. Syntheses of fimbricalyxlactone B, isoshihunine and numerous biologically-relevant heterocycles show the value of the methods, while TA-spectroscopy and TD-DFT studies provide mechanistic insights on their wavelength dependence.

Visible-light-mediated defluorinative cyclization of α-fluoro-β-enamino esters catalyzed by 4-CzIPN

Using 4-CzIPN as an energy transfer (EnT) photocatalyst and α-fluoro-β-enamino esters as the substrates, a mild 6π-photocyclization/defluorination of N-aryl enamines was carried out to efficiently construct indoles without oxidant and...