Stereospecific preparation of symmetrical (1Z, 3Z)- and (1E, 3E)-2,3-difluoro-1,4-disubstituted-buta-1,3-dienes from 1-bromo-1-fluoroalkenes

A straightforward method to prepare symmetrical (1Z, 3Z)- and (1E, 3E)-2,3-difluoro-1,4-disubstituted-buta-1,3-dienes is described. High E/Z ratio 1-bromo-1-fluoroalkenes, prepared by isomerization from the E/Z ≈ 1:1 isomeric mixtures, reacted with Bu₃SnSnBu₃ and Pd(PPh₃)₄ to afford (1Z, 3Z)-2,3-difluoro-1,4-disubstituted-buta-1,3-dienes in good yield. (Z)-1-Bromo-1-fluoroalkenes, which were prepared by kinetic reduction from 1-bromo-1-fluoroalkenes (E/Z ≈ 1:1), can undergo similar reaction with Bu₃SnSnBu₃ and Pd(PPh₃)₄/CuI to prepare (1E, 3E)-2,3-difluoro-1,4-disubstituted-buta-1,3-dienes.     

Palladium-catalyzed synthesis of quinoxaline derivatives

A palladium-catalyzed reductive N-heteroannulation of enamines derived from 2-nitrobenzenamines forming mixtures of 1,2-dihydroquinoxalines and 3,4-dihydroquinoxalin-2-ones is described. The reactions are performed using bis(dibenzylideneacetone)palladium(0), 1,3-bis(diphenylphosphino)propane, and 1,10-phenanthroline in DMF under 6 atm of carbon monoxide at 70 °C.     

Palladium-Catalyzed Tandem Cyclization Strategy for the Assembly of 3-Halo-1,2,5-triarylpyrroles from N-Alkylanilines and Haloalkynes

This report discloses a distinctive palladium-catalyzed sequential tandem cyclization reaction of two molecular haloalkynes and one molecular N-alkylanilines, leading to the efficient assembly of various 3-halo-1,2,5-triarylpyrrole derivatives. Two carbon-carbon triple bonds and one carbon-halogen bond in two molecular haloalkynes are transformed conveniently in one single step, which may involve the aminoalkynylation of haloalkyne and cyclization of the newly formed enyne intermediate. The high chemo- and regioselectivities, good functional group tolerance and late-stage modification of the halopyrrole products further illustrate the synthetic value of this strategy.