Palladium‐Catalyzed Cascade Reaction of o ‐Bromobenzaldehydes with N ‐Sulfonylhydrazones: An Efficient Approach to the Naphthalene Skeleton

Palladium-catalyzed cascade cyclization of α,β-unsaturated N-tosylhydrazones with iodoarenes: access to 2H-chromenes and 2H-quinolines

A palladium-catalyzed cascade reaction of α,β-unsaturated N-tosylhydrazones with iodoarene derivatives containing a nucleophilic group has been developed, which provides facile access to 2H-chromenes and 2H-quinolines, respectively. Additionally, the double Pd-carbene migratory insertion/nucleophilic substitution processes for the synthesis of a ternary heterocyclic skeleton were possible in the developed catalytic system.

PPh3-Mediated Cascade Reaction of 2-Alkynylnitrobenzenes and Thioureas for the Construction of Imidazo[4,5-b]indole-2-thiones

A simple method for the preparation of imidazo[4,5-b]indole-2-thiones from 2-alkynylnitrobenzenes and thioureas is described. In the reaction, a Wittig-like process was triggered by PPh₃ and followed by a cyclization step. The products were afforded in yields of 70-98% under mild conditions. Additionally, the 2-alkynylnitrobenzenes were stable and could be prepared via a simple coupling step.

1,1,1,3,3,3-Hexafluoro-2-propanol (HFIP)-Assisted Catalyst-Free Sulfonation of Allylic Alcohols with Sulfinyl Amides

A highly regioselective and catalyst-free sulfonation of allylic alcohols with sulfinyl amides has been realized. Such a mix-and-go procedure provides a convenient approach to synthetically various allylic sulfones under mild reaction conditions. Furthermore, this novel reaction shows ample substrate scope and outstanding functional group tolerance and could also be scaled-up. Meanwhile, it is the first example that sulfinyl amides act as a powerful sulfur nucleophile in the reactions. 1,1,1,3,3,3-Hexafluoro-2-propanol (HFIP) as a solvent plays a critical role in allylic sulfonation.

Carbene-catalyzed atroposelective synthesis of axially chiral styrenes

Axially chiral styrenes bearing a chiral axis between a sterically non-congested acyclic alkene and an aryl ring are difficult to prepare due to low rotational barrier of the axis. Disclosed here is an N-heterocyclic carbene (NHC) catalytic asymmetric solution to this problem. Our reaction involves ynals, sulfinic acids, and phenols as the substrates with an NHC as the catalyst. Key steps involve selective 1,4-addition of sulfinic anion to acetylenic acylazolium intermediate and sequential E-selective protonation to set up the chiral axis. Our reaction affords axially chiral styrenes bearing a chiral axis as the product with up to > 99:1 e.r., > 20:1 E/Z selectivity, and excellent yields. The sulfone and carboxylic ester moieties in our styrene products are common moieties in bioactive molecules and asymmetric catalysis.

Silver-catalyzed [4 + 3] cycloaddition of 1,3-dienes with alkenyl-N-triftosylhydrazones: a practical approach to 1,4-cycloheptadienes

A formal [4 + 3] cycloaddition of 1,3-dienes with alkenyl-N-triftosylhydrazones was developed using silver catalysis, producing a broad spectrum of complex 1,4-cycloheptadienes with high yields and predictable stereochemistry.

Tandem Synthesis of 1,3-Disubstituted Naphthalenes via TfOH-Promoted Directed-Aldol and Friedel-Crafts Reactions

A TfOH-promoted tandem synthesis of 1,3-disubstituted naphthalenes is developed via a directed-aldol reaction and a Friedel-Crafts reaction. Two new C-C bonds and one new benzene ring are created efficiently in one pot due to the discovery of a TfOH-promoted highly chemoselective directed-aldol reaction between two different ketones with α-hydrogens.

Facile access to 2,2-diaryl 2H-chromenes through a palladium-catalyzed cascade reaction of ortho-vinyl bromobenzenes with N-tosylhydrazones

A palladium-catalyzed cascade reaction of ortho-vinyl bromobenzenes with N-tosylhydrazones has been developed, which provides a facile approach to 2,2-disubstituted 2H-chromenes. The migration of palladium from the aryl to vinyl position is crucial, as the in situ produced vinyl palladium intermediate could further react with diazo compounds to generate the reactive species for the sequential annulation.