Silver‐catalyzed three‐component, tandem reactions of 4‐alkynyl‐2‐oxo‐2H‐chromene‐3‐carbaldehydes, amines and various nucleophiles result in the formation of highly functionalized chromeno[3,4‐c]pyridin‐5‐ones in high yields. Gold‐catalyzed [4+2] cycloadditions of 4‐alkynyl‐2‐oxo‐2H‐chromene‐3‐carbaldehydes with alkynes or alkenes have also been achieved to afford benzo[c]chromen‐6‐ones efficiently.
A potassium hydroxide/dimethyl sulfoxide (KOH/DMSO) superbase‐promoted method for the synthesis of 2‐substituted benzothiophenes has been developed via photoinduced intermolecular annulation of 2‐halothioanisoles with terminal alkynes at ambient temperature. The present protocol uses commercially available 2‐halothioanisoles as substrates and visible light as energy force, which offers a wide range of benzothiophenes regioselectively in moderate to good yields. Such a facile and effective transformation will provide an environment‐friendly approach to the synthesis of benzothiophene derivatives.
1‐Bromo‐2‐(cyclopropylidenemethyl)benzenes react with 2‐alkynylphenols under palladium catalysis, leading to indeno[1,2‐c]chromenes in moderate to good yields. The molecular complexity and diversity can be introduced efficiently from easily available starting materials.
An efficient route to 4‐cyanoquinolines via a palladium‐catalyzed cyanative reaction of 2‐alkynylbenzaldimines with isocyanides has been developed. The transformation proceeds through 6‐endo cyclization, isocyanide insertion, and cyanation. 4‐Amidylisoquinolines can be generated as well if water is involved in the reaction.
Through an unexpected CC bond migration, 2(E)‐enals were efficiently prepared highly stereoselectively in moderate to good yields via the sodium iodide/tert‐butyl(dimethyl)silyl chloride (NaI/TBSCl)‐mediated reaction of the easily available 2,3‐allenols. Based on a careful mechanistic study, including control experiments and deuterium‐labeling experiments, an electron‐withdrawing substituent group in the 4 position has been proven to be crucial and a possible mechanism has been proposed.
An efficient and concise one‐pot strategy for the direct alkylation of quinoline N‐oxides via palladium‐catalyzed dual C H bonds activation has been developed. This methodology provides quinoline‐containing heterocyclic molecules in moderate to excellent yields.
