Xiao Geng

Dual Roles of Methyl Ketones in Radziszewski-Type Reaction: Formal [2 + 1 + 1 + 1] Synthesis of 1,2,5-Trisubstituted Imidazoles

A highly efficient molecular iodine mediated Radziszewski-type reaction of methyl ketones, anilines, and tosylmethyl isocyanide has been developed. This protocol represents an elegant molecular fragment assembly of imidazoles via a formal [2 + 1 + 1 + 1] annulation. It is the first example where methyl ketones serve as the α-dicarbonyl compounds and aldehydes in Radziszewski-type reactions.

Iodine-Promoted Oxidative Cross-Coupling of Unprotected Anilines with Methyl Ketones: A Site-Selective Direct C-H Bond Functionalization to C4-Dicarbonylation of Anilines.

An unprecedented direct dual C-H bond functionalization of unprotected anilines and methyl ketones has been demonstrated. It is the first example of iodine-promoted highly chemo- and site-selective oxidative C-H/C-H cross-coupling of anilines and methyl ketones to furnish the C4-dicarbonylation of anilines in moderate to good yields. Moreover, coproduct HI acted as a catalyst in the reaction. The salient feature of this approach is unprecedented C-H functionalization rather than N-H functionalization of unprotected anilines.

Diamination/Oxidative Cross-Coupling/Bicyclization of Anilines and Methyl Ketones: Direct I2-Promoted Synthesis of 1,2-Fused Oxindoles

An I2-promoted domino bicyclization approach via multiple sequential C-H functionalization was serendipitously discovered for the synthesis of 1,2-fused oxindoles from methyl ketones and anilines. This approach was optimized, resulting in a concise and atom-economical approach for the one-pot construction of 1,2-fused oxindoles from methyl ketones and anilines rather than using preexisting indolin-3-ones or indoles. Mechanistic studies revealed that the key step involved an oxidative cross-coupling between in situ generated phenylglyoxal and α,α-diaminoketone.

I2-Promoted Povarov-Type Reaction Using 1,4-Dithane-2,5-diol as an Ethylene Surrogate: Formal [4 + 2] Synthesis of Quinolines

A highly efficient I2-promoted formal [4 + 2] cycloaddition has been developed for the synthesis of 2-acylquinolines from methyl ketones and arylamines using 1,4-dithane-2,5-diol as an ethylene surrogate. Moreover, the investigation of the mechanism suggested that this reaction occurred via an iodination/Kornblum oxidation/Povarov/aromatization sequence. It is noteworthy that the arylamine substrate also played an important role in promoting the reaction.

Direct Oxidative Cleavage of Multiple Csp3–H Bonds and a C–C Bond in 2-(Pyridin-2-yl)acetate Derivatives: Formal [3 + 1 + 1] Synthesis of 3-(Pyridin-2-yl)indolizine Skeletons

A novel iodine-promoted oxidative cross-coupling/cyclization of 2-(pyridin-2-yl)acetate derivatives and methyl ketones via the cleavage of multiple Csp3-H bonds has been developed, which also achieved efficient cleavage of a C-C bond in the 2-(pyridin-2-yl)acetate derivatives. This protocol represents an elegant molecular fragment assembly of diverse 3-(pyridin-2-yl)indolizines via a formal [3 + 1 + 1] annulation. Notably, the pyridine derivatives serve two pivotal roles to provide two fragments to construct 3-(pyridin-2-yl)indolizine skeletons, rather than the single role in building common indolizines.

Synergistic I2/Amine Promoted Povarov-Type Reaction for the Synthesis of 2-Acyl-3-aryl(alkyl)quinolines Using Aryl(alkyl)acetaldehydes as Alkene Surrogates

A synergistic I2/amine promoted formal [4 + 2] cycloaddition of methyl ketones, arylamines, and aryl(alkyl)acetaldehydes as alkene surrogates has been established. This protocol allowed the modular synthesis of various 2-acyl-3-aryl(alkyl)quinolines, rather than 2,4-substituted quinolines. Notably, the arylamines not only participated as reactants in this reaction but also acted as indispensable catalysts to promote enamine formation. Moreover, mechanistic investigation suggested that the reaction occurred via an iodination/Kornblum oxidation/Povarov/aromatization sequence.

Iodine-promoted sequential dual oxidative Csp3–H amination/Csp3–H iodination reactions: efficient synthesis of 1-iodoimidazo[1,5-a]pyridines

An iodine-promoted sequential dual oxidative Csp3–H amination of aryl methyl ketones and Csp3–H iodination of pyridin-2-ylmethylamines have been realized for the first time. This simple and efficient approach constructed 1-iodoimidazo[1,5-a]pyridines in moderate to good yields. Based on the preliminary experimental results, a self-sequenced process featuring the iodination/Kornblum oxidation/dual amination/oxidation/iodination mechanism was proposed.

Iodine-Catalyzed Oxidative Coupling To Construct C–O Bonds for the Synthesis of 2,3-Dihydrooxepines

The iodine-catalyzed catalytic formal [3 + 3 + 1] cycloaddition for the preparation of a seven-membered O-heterocyclic ring is presented, which is an achievement of methyl and carbonyl group reactivity of 3-methyl-5-pyrazolones to forge the Csp3-O bond. This novel protocol provides a straightforward and efficient access to structurally diverse fused O-heterocycles through an iodine-catalyzed iodination/Kornblum oxidation/oxidative coupling/C-O bond formation cascade reaction. This approach demonstrates the unprecedented concurrent realization of the unique reactivity among the methyl, methylene, and carbonyl groups in 3-methyl-5-pyrazolones for the construction of 2,3-dihydrooxepine rings. Moreover, a broad substrate scope displays a graceful diversity-oriented synthetic approach.

Synthesis of Pyrrole-2-carbaldehyde Derivatives by Oxidative Annulation and Direct Csp3–H to C═O Oxidation

An efficient and practical de novo synthesis of pyrrole-2-carbaldehyde skeletons featuring oxidative annulation and Csp3-H to C═O oxidation is presented, exemplified by the preparation of pyrrole-2-carbaldehyde derivatives from aryl methyl ketones, arylamines, and acetoacetate esters. Preliminary mechanistic investigations indicate that the aldehyde oxygen atom originates from oxygen. Moreover, the developed scalable approach provides a distinct advantage over traditional oxidative functionalization of C-H moieties, avoiding the use of stoichiometric quantities of hazardous oxidants.

NaHS.nH2O-Induced Umpolung: The Synthesis of 2-Acyl-3-aminoindoles from Aryl Methyl Ketones and 2-Aminobenzonitriles

An efficient method for constructing 2-acyl-3-aminoindoles from methyl ketones and 2-aminobenzonitriles is described, in which NaHS·nH2O is used as a novel umpolung reagent for the first time in organic synthesis. Mechanistic studies revealed that the key step involved an Eschenmoser sulfide contraction reaction.