Copper-catalyzed regioselective alkylation of heteroarenes with functionalized alkyl halides

The Cu-catalyzed regioselective alkylation of heteroarenes with functionalized primary, secondary, and tertiary alkyl halides is reported. The reaction proceeds via the copper-catalyzed addition of alkyl radicals to a wide range of heteroarenes, including coumarin, quinolinone, naphthoquinone, and benzofuran derivatives, with a broad substrate scope and wide functional group tolerance.     

Palladium-catalyzed direct C-H bond alkynylations of heteroarenes using gem-dichloroalkenes

Palladium-catalyzed direct alkynylations of heteroarenes were accomplished with inexpensive gem-dichloroalkenes as user-friendly electrophiles, which set the stage for a modular, step-economical synthesis of diversely decorated heteroaryl alkynes with ample scope.     

Synthesis of ferrocenylarenes and heteroarenes through nucleophile induced ring transformation of 2H-pyran-2-ones

The synthesis of various ferrocenylarenes (3, 5a, 6) and heteroarenes (5b, c, 7) from 6-ferrocenyl-4-methylsulfanyl-2H-pyran-2-one-3-carbonitrile 1 through nucleophile induced ring transformation reactions has been delineated.     

Regioselective formylation of 1,3-disubstituted benzenes through in situ lithiation

A facile method of regioselective formylation of disubstituted benzene via in situ deprotonation/metalation using n-BuLi/TMEDA/DIPA has been developed. Effect of different electron withdrawing and electron donating substituents in 1,3-interrelated aromatic system was studied; the metalation mostly occurred at the 2-position to afford the desired products in high yields.     

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 oxidative homocoupling of 2-arylquinazolinones

Pd-catalyzed oxidative homocoupling of 2-arylquinazolinones was successfully developed for the direct construction of biaryls via CH bond activation. New well-defined structure that possessed two quinazolinone units was obtained with high efficiency and atomic economy. The protocols offer an efficient approach to the synthetically useful and functionalized biaryls in good yields using quinazolinone as a directing group.     

Ruthenium-catalyzed direct C-H bond arylations of heteroarenes

Ruthenium-catalyzed C-H bond arylations of indoles, thiophenes, and pyrroles were accomplished in a highly chemo- and site-selective manner through the use of removable directing groups.     

Palladium-catalyzed direct heteroarylation of chloropyridines and chloroquinolines

The direct coupling of aryl chlorides with heteroarenes would be a considerable advantage for sustainable development due to their lower cost, lower mass, the wider diversity of available compounds and also because of the formation of only HCl associated to a base as by-product and the reduction of the number of steps to prepare these compounds. We observed that through the use of PdCl(dppb)(C₃H₅) as a catalyst, a range of heteroaryl derivatives undergoes coupling via C-H bond activation/functionalization reaction with chloropyridines or chloroquinolines in low to high yields. This air-stable catalyst can be used with a wide variety of substrates. The position of the chloro substituent on pyridines has a minor influence on the yields. On the other hand, the nature on the heteroaryl derivative has a large influence. The highest yields were obtained using benzoxazole, thiophene or thiazole derivatives. The coupling of chloropyridines with furans also gave the expected products, but in low to moderate yields.     

Palladium-catalyzed syntheses of tetrahydrocarbazolones as advanced intermediates to carbazole alkaloids

Two sequential palladium-catalyzed reactions, an intermolecular Stille cross-coupling followed by a recently developed palladium-catalyzed reductive N-heteroannulation, have been employed as the key synthetic steps toward six tetrahydrocarbazolones. The products are advanced intermediates toward a number of naturally occurring carbazole alkaloids.     

Palladium-catalyzed hydroarylation of alkynes with arylboronic acids

Reaction of symmetrical and unsymmetrical alkynes with arylboronic acids, using PdCl₂ as catalyst source and i-Pr₂NPPh₂ as ligand, afforded trisubstituted alkenes with regioselectivity in good to excellent yields without a common additional acetic acid. Its efficiency has been demonstrated by its good functional groups, high yield and crowded substrates.     

Palladium-catalyzed C-H perfluoroalkylation of arenes

A new Pd-catalyzed reaction for the coupling between perfluoroalkyl iodides (R(F)I) and simple aromatic substrates is described. The perfluoroalkylated arene products are obtained in good to excellent yields in the presence of a phosphine-ligated Pd catalyst and Cs(2)CO(3) as a base. The development, optimization, scope, and preliminary mechanistic studies of these transformations are reported.     

Radical dearomatization of arenes and heteroarenes

The stannane-mediated benzeneselenol-catalyzed addition of aryl iodides to a range of arenes and aromatic hetereocycles has been studied. With furan, thiophene, and several carbocyclic arenes, the addition takes place with quenching of the adduct radical by the catalytic selenol leading to moderate yields of aryl-dihydroarenes. With nitrogen heterocycles, on the other hand, it was not possible to suppress aromatization of the adduct radical and fully aromatized products were isolated. Aryl iodides bearing hydrogen bond donating groups in the ortho-position add to nitrogen heterocycles with high selectivity ortho- to the nitrogen, affording a simple one-step synthesis of potential chelating ligands. While 2-iodophenol is an excellent aryl radical source in these reactions, the homologous 1-iodo-2-naphthol fails owing to its reaction with diphenyl diselenide, which gives 1-phenylseleno-2-naphthol in high yield.