Zn(OAc)2-Catalyzed C3-Carbonylacetylation of Indoles with α-Diazoketones Involving Wolff Rearrangement

Cascade Wolff Rearrangement/Acylation: A Metal-Free and Eco-Friendly Approach for 4-Hydroxy-pyrazolo[3,4-b]pyridin-6-ones and N-Pyrazole Amides Synthesis from 5-Aminopyrazoles and α-Diazoketones

A highly chemoselective cascade Wolff rearrangement/acylation reaction between 5-aminopyrazoles and diazo compounds has been developed. The protocol can facilitate the switchable synthesis of 4-hydroxy-pyrazolo[3,4-b]pyridin-6-ones and N-pyrazole amides with the merits of a broad substrate scope, high functional group compatibility, and green and sustainable performance manner. All reactions proceeded efficiently without any catalyst and additives (acid and base) and resulted in the release of benign N₂, wherein diethyl carbonate served as a green benign solvent.

Microwave-accelerated and efficient synthesis of structurally diverse N-(2,2-diphenylvinyl)-β-oxoamides

N-(2,2-Diphenylvinyl)-β-oxoamides are both the structural moiety of biologically active compounds and important synthetic intermediates. Structurally diverse N-(2,2-diphenylvinyl)-β-oxoamides are prepared efficiently from 2-diazo-1,3-dicarbonyl compounds and N-alkyl-2,2-diphenylaziridines via an electrophilic ring opening reaction under two different reaction conditions of reflux and microwave irradiation. 2-Diazo-1,3-dicarbonyl compounds undergo the Wolff rearrangement under heating to generate α-oxoketenes, which electrophilically react with N-alkylaziridines to directly produce structurally diverse N-(2,2-diphenylvinyl)-β-oxoamides in good to excellent yields under microwave irradiation. Microwave irradiation accelerates the reaction obviously and efficiently. Both 2-diazo-1,3-diketones and alkyl 2-diazo-3-oxoalkanoates work well. The reaction is catalyst-free and highly atom economical, involves only loss of nitrogen and does not require additives. The products are useful synthons for the convenient preparation of multisubstituted β-lactam derivatives.

Copper-Catalyzed Annulation of Indolyl α-Diazocarbonyl Compounds Leads to Structurally Rearranged Carbazoles

Indolyl α-diazocarbonyl compounds have proven to be effective starting materials for the construction of various 2,3-ring fused indole frameworks. Activation of the diazo functional group under metal catalysis generates a spiro-cyclic indolenine-type intermediate which rearranges to provide two distinct carbazoles upon oxidation. The current study investigates the effects of the catalyst as well as the substituents on the migratory group involved in controlling the selectivity of the rearrangement.

Catalyst-free synthesis of α,α-disubstituted carboxylic acid derivatives under ambient conditions via a Wolff rearrangement reaction

Herein, a hexafluoroisopropanol (HFIP)-promoted Wolff rearrangement reaction was developed, delivering various α,α-disubstituted carboxylic acid derivatives in good to excellent yields.

Selective Synthesis of Pyrano[3,2-b]indoles or Cyclopenta[b]indoles Tethered with Medium-Sized Rings via Cascade C-C σ-Bond Cleavage and C-H Functionalization

Highly atom-economical tandem reactions have been developed for the synthesis of pyrano[3,2-b]indoles or cyclopenta[b]indoles tethered with 7-, 8-, or 9-membered rings. These reactions first undergo a carbon-carbon σ-bond cleavage reaction of cyclic β-ketoesters. Next, in the presence of CuCl₂ and Ag₂CO₃, intramolecular O-H/C-H coupling occurs to give pyrano[3,2-b]indoles. This is the first example for capture of the enoloxyl radical of the intramolecular C-O bond formation reaction, whereas C3 nucleophilic addition afforded cyclopenta[b]indoles using TsOH·H₂O.

Metal-free tandem carbene N-H insertions and C-C bond cleavages

A metal-free C-H [5 + 1] annulation reaction of 2-arylanilines with diazo compounds has been achieved, giving rise to two types of prevalent phenanthridines via highly selective C-C cleavage. Compared to the simple N-H insertion manipulation of diazo, this method elegantly accomplishes a tandem N-H insertion/SEAr/C-C cleavage/aromatization reaction, and the synthetic utility of this new transformation is exemplified by the succinct syntheses of trisphaeridine and bicolorine alkaloids.

Rhodium(i)-catalyzed vinylation/[2 + 1] carbocyclization of 1,6-enynes with α-diazocarbonyl compounds

A sequential Rh(i)-catalyzed vinylation/[2 + 1]carbocyclization between enynes and diazo compounds has been developed. This transformation features a wide range of enynes and acceptor/acceptor diazo compounds, providing easy access to versatile vinyl-substituted azabicyclo[3.1.0]hexanes having a broad tolerance to functional groups.

Zn(OAc)2-catalyzed tandem cyclization of isocyanides, α-diazoketones, and anhydrides: a general route to polysubstituted maleimides

A zinc-catalyzed three-component reaction of isocyanides, α-diazoketones, and anhydrides has been realized as a novel and efficient method for the synthesis of polysubstituted maleimides.