Silver mediated direct C–H arylation of 3-bromoisothiazole-5-carbonitrile

Palladium catalyzed direct C–H arylation of 3-bromoisothiazole-5-carbonitrile with aryl/hetaryl iodides in the presence of AgF gave 13 4-aryl/hetaryl-3-bromoisothiazole-5-carbonitriles. The scope of this arylation was investigated and explanations for the limitations proposed. 3-Bromoisothiazole-5-carboxamide was isolated as a side-product, and its formation was attributed to Ag⁺-catalyzed hydration of the C-5 nitrile. The analogous phenylation of 3-chloroisothiazole-5-carbonitrile and 3-bromoisothiazole-4-carboxamide gave 3-chloro-4-phenylisothiazole-5-carbonitrile and 3-bromo-5-phenylisothiazole-4-carboxamide in 83 and 64% yields, respectively.     

NH4I-catalyzed chalcogen(S/Se)-functionalization of 5-membered N-heteroaryls under metal-free conditions

Herein, we described the NH₄I-catalyzed CH bond chalcogenation of N-heteroaryls in the presence of a minimum amount of DMSO/H₂O/acetic acid as additives (2.5/2.5/1?M equiv., respectively), under metal-free conditions. Under optimized conditions, a wide variety of sulfenyl/selenyl imidazo[1,2-α]pyridines were prepared in very good yields. Moreover, the present approach was also highly efficient for the chalcogenation of different 5-membered N-heteroaryls, e.g., indole, imidazothiazole, indazole and imidazopyrimidine derivatives.     

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.     

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.     

Highly efficient iodine-catalyzed hydroarylation of arenes with styrenes

Iodine mediates the hydroarylation of styrenes with arenes and heteroarenes to afford 1,1-diarylalkanes in good to high yields. Details regarding the substrate scope and selectivity of this hydroarylation reaction are discussed.     

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.     

η2(π)‐Coordination of a Bis‐Phosphonio‐Benzophospholide Cation: A Novel Complexation Mode for Unsaturated Phosphorus Heterocycles

The bis‐phosphonio‐benzo[c]phospholide tetraphenylborate 4 [BPh₄] reacts with CpCo(C₂H₄)₂ to form a chelate complex [Co(η⁵–Cp)(κ²P,η²(P=C) –4 )][BPh₄] ( 6 [BPh₄]) which was characterized by means of spectroscopic techniques and a single crystal X‐ray diffraction study. The observed η²(π)‐coordination of the benzophospholide moiety in the cation 6 is highly unusual for aromatic phosphorus heterocycles. The structural data suggest a pronounced coordination‐induced localization of π‐electrons in the condensed ring system.     

Palladium-catalyzed C-H formylation of electron-rich heteroarenes through radical dichloromethylation

A novel palladium-catalyzed C-H formylation of electron-rich N-, O-, and S-containing heteroarenes has been developed. The key to success is that the commercially available BrCHCl₂ was used as a stoichiometric carbonyl source. Mechanistic investigations indicated that different from the known Reimer-Tiemann reaction, this net C-H formylation proceeded through an electrophilc radical-type path.     

A general and efficient synthesis of substituted fluorenes and heterocycle-fused indenes containing thiophene or indole rings utilizing a Suzuki-Miyaura coupling and acid-catalyzed Friedel-Crafts reactions as key steps

A general and efficient synthesis of fluorenes or heterocycle-fused indenes including 3-thia-cyclopenta[a]indenes, 9-thia-indeno[1,2-a]indenes, 5,6-dihydroindeno[2,1-b]indoles has been developed. This methodology is realized by a multistep protocol involving first preparation of ortho-formylbiaryls through Suzuki-Miyaura coupling of o-bromobenzaldehydes with arylboronic acids or the coupling of aryl halides with 2-formylbenzene boronic acid, this is followed by Grignard addition and Friedel-Crafts cyclization reactions catalyzed by Brønsted or Lewis acid to form the desired fluorene or indene rings. The method offers several advantages such as high yields, high selectivities, mild reaction conditions, easily accessible starting materials, and so on.