Substituent Electronic Effects Govern Direct Intramolecular C–N Cyclization of N-(Biphenyl)pyridin-2-amines Induced by Hypervalent Iodine(III) Reagents

Synthesis and Mechanistic Investigation of Bipyrazolo[1,5-a]pyridines via Palladium-Catalyzed Cross-Dehydrogenative Coupling of Pyrazolo[1,5-a]pyridines

The synthesis of a range of 3,3'-bipyrazolo[1,5-a]pyridine derivatives via direct cross-dehydrogenative coupling of pyrazolo[1,5-a]pyridine precursors is herein presented. This simple and efficient methodology involving palladium(II)-catalyzed C-H bond activation showed good functional group tolerance and product yield (up to 94%). Through the mechanistic insights gained from both kinetic isotope effect experimental studies and density functional theory calculations, a plausible reaction mechanism was outlined. Furthermore, subsequent derivatizations of the resulting 7,7'-diaryl-3,3'-bipyrazolo[1,5-a]pyridines, executed by performing palladium-mediated ortho C-H bond activation followed by hypervalent iodine-induced chlorination, rendered this series of compounds more extended π-conjugation and twisted conformations. Our study on these bipyrazolo[1,5-a]pyridine-based luminogens provides new opportunities for tailor-made organic luminescent materials.

Iodine-mediated oxythiolation of o-vinylanilides with disulfides for the synthesis of benzoxazines

An efficient iodine-mediated oxythiolation of o-vinylanilides with disulfides was developed. By virtue of this method, a series of thio-tethered benzoxazine derivatives were synthesized in good to excellent yields. The reaction features high yields, is metal-free, and has a wide substrate scope.

An efficient iodine-mediated oxythiolation of o-vinylanilides with disulfides was developed. The reaction features high yields, is metal-free, and has a wide substrate scope.

Hypervalent iodine(iii)-mediated oxidative dearomatization of 2H-indazoles towards indazolyl indazolones

We accomplished a [bis(trifluoroacetoxy)iodo]benzene mediated oxidative dearomatization of 2H-indazoles, obtaining a new family of N-1 indazolyl indazolone derivatives in good to excellent yields through C–N and C–O bond formations.

Recent progress in (hetero)arene cation radical-based heteroarene modification

The transformation of (hetero)arene cation radicals has become a powerful tool for the construction of highly functionalized (hetero)arenes. These (hetero)arene cation radicals could be generated under electrochemical, photochemical or chemical oxidation systems. The in situ generated (hetero)arene cation radicals can be attacked by various nucleophiles, such as (hetero)aromatics and anions, yielding structurally diverse molecules. Recently, a large number of impressive heteroarene modifications have been designed by this strategy. This review summarizes the advances in heteroarene modification via reactions of in situ formed (hetero)arene cation radicals, ranging from 2010 to 2020.

Pd-catalyzed versus uncatalyzed, PhI(OAc)2-mediated cyclization reactions of N6-([1,1'-biaryl]-2-yl)adenine nucleosides

In this work we have assessed reactions of N⁶-([1,1'-biaryl]-2-yl)adenine nucleosides with Pd(OAc)₂ and PhI(OAc)₂, via a Pd^II/Pd^IV redox cycle. The substrates are readily obtained by Pd/Xantphos-catalyzed reaction of adenine nucleosides with 2-bromo-1,1'-biaryls. In PhMe, the N⁶-biarylyl nucleosides gave C6-carbazolyl nucleoside analogues by C-N bond formation with the exocyclic N⁶ nitrogen atom. In the solvent screening for the Pd-catalyzed reactions, an uncatalyzed process was found to be operational. It was observed that the carbazolyl products could also be obtained in the absence of a metal catalyst by reaction with PhI(OAc)₂ in 1,1,1,3,3,3-hexafluoroisopropanol (HFIP). Thus, under Pd catalysis and in HFIP, reactions proceed to provide carbazolyl nucleoside analogues, with some differences. If reactions of N⁶-biarylyl nucleoside substrates were conducted in MeCN, formation of aryl benzimidazopurinyl nucleoside derivatives was observed in many cases by C-N bond formation with the N1 ring nitrogen atom of the purine (carbazole and benzimidazole isomers are readily separated by chromatography). Whereas Pd^II/Pd^IV redox is responsible for carbazole formation under the metal-catalyzed conditions, in HFIP and MeCN radical cations and/or nitrenium ions can be intermediates. An extensive set of radical inhibition experiments was conducted and the data are presented.

Benzimidazopurine nucleosides from N6-aryl adenosine derivatives by PhI(OAc)2-mediated C-N bond formation, no metal needed

The reaction of a variety of N⁶-aryl 2'-deoxyadenosine and adenosine derivatives with PhI(OAc)₂ in 1,1,1,3,3,3-hexafluoro-2-propanol provides a facile access to benzimidazopurine nucleoside analogues by metal-free C-N bond formation with a purinyl nitrogen atom. These reactions likely proceed via radical-cation/radical processes as indicated by radical inhibition experiments.

Organoiodine reagent-promoted intermolecular oxidative amination: synthesis of cyclopropyl spirooxindoles

An organoiodine-promoted intramolecular direct oxidative C(sp²)–N cross-coupling reaction was developed for the preparation of cyclopropyl spirooxindoles from readily available secondary cyclopropyl carboxamides.

The Conversion of 4-Anilinoquinazoline- and 3-Aryl-4-imino-3,4-dihydro-quinazoline-2-carbonitriles into Benzo[4,5]imidazo[1,2-c]quinazoline-6-carbonitriles via Oxidative and Nonoxidative C-N Couplings

Benzo[4,5]imidazo[1,2-c]quinazoline-6-carbonitriles are prepared in high yields via three new routes: (1) a Cu(OTf)2 (0-5 mol %) catalyzed hypervalent iodine [PhI(OTf)2] mediated oxidative coupling of 4-anilinoquinazoline-2-carbonitriles in neat trifluoroacetic acid (TFA); (2) a Pd(OAc)2 (10 mol %) or CuI (10 mol %) mediated nonoxidative coupling of 4-(2-bromoanilino)quinazoline-2-carbonitrile; and (3) a nonoxidative Pd(Ar3P)3 [Ar = 3,5-(F3C)2C6H3] [aka Superstable Pd(0) Catalyst] (10 mol %) mediated intramolecular C-N cyclization of 3-(2-bromophenyl)-4-imino-3,4-dihydroquinazoline-2-carbonitriles. All new compounds are fully characterized.

Aminations with Hypervalent Iodine

Recent progress in the area of hypervalent iodine-mediated and catalyzed amination reaction of hydrocarbons is reviewed. These reactions comprise processes under both intra and intermolecular control and include the functionalization of aromatic C-H bonds as well as conversion of sp-, sp(2)-, and sp(3)-hybridized carbon atoms. These developments demonstrate that hypervalent iodine(III) methodology has reached a high level in amination chemistry. The individual reactions are discussed with a focus on mechanistic details and emphasis is made to the underlying hypervalent iodine reagents, for which structural information is available.