An iron(III)‐catalyzed C‐3 functionalization of flavones has been achieved using tert‐butyl peroxybenzoate (TBPB)/potassium persulphate (K2S2O8) oxidant combinations with a suitable solvent. In the presence of iron(III)/tert‐butyl peroxybenzoate/potassium persulphate, the reaction of flavones in cycloalkanes afforded exclusive C‐3 cycloalkylation via C –C coupling, whereas the solvent N,N‐dialkylformamide provided C‐3 amidation via C –C coupling. Under identical reaction conditions just by switching the solvent to chlorobenzene, C‐3 methylated flavones were obtained where tert‐butyl peroxybenzoate (TBPB) served as the source of the methyl group.
N‐Propargyl‐ and N‐homoallenyl‐2‐bromo‐β‐tryptamines undergo gold(I)‐catalyzed dearomatizing cyclizations to afford 2‐bromospiroindolenines that are in situ hydrolyzed to furnish spirooxindoles in a one‐pot process. Tryptophane derivatives (R2=CO2Et) led upon cyclization to chiral spirooxindoles in excellent diastereoselectivities.
N‐Allyltetrahydro‐β‐carbolines bearing a pendant allene undergo unprecedented gold(I)‐catalyzed cyclizations proceeding with an allyl migration from the nitrogen to the allene moiety. The initial product of the gold‐catalyzed cyclization evolves either via isomerization or Cope rearrangement, leading to different scaffolds. Density function theory (DFT) calculations established that the allyl migration occurs in an asynchronous suprafacial manner.
The improved synthesis of γ‐, δ‐ and ϵ‐lactones using a dinuclear N‐heterocyclic carbene (NHC)‐gold(I) catalyst is reported. This solvent‐free process provides access to γ‐ and δ‐lactones in high regio‐ and stereoselectivity. Reactions were performed at low catalyst loadings and without the need for any additives. The use of a digold pre‐catalyst provides a new synthetic route to functionalised ϵ‐lactones, poorly accessible using previous methodologies.
The synthesis of biologically relevant homophthalimide and 3‐aminoisocoumarin nuclei via palladium‐catalyzed carbonylation of 2‐(2‐iodoaryl)acetamides has been developed. The degree of N‐substitution on the starting amide substrate dictates whether C−N or C−O coupling takes place in the final step of the catalytic cycle giving rise to each type of heterocycle. The introduction of a second C−halogen bond in the starting acetamides allows a catalytic cascade double carbonylation involving a C−H activation step to give fused heterocyclic structures.
2,3‐Dihydroindenes and isoindolines are important skeletons present in medicinal and synthetic chemistry. In this paper, an acetyl bromide promoted metal‐free construction of 2,3‐dihydroindenes and isoindolines with high synthetic efficiency is developed.
A palladium‐catalyzed domino strategy has been developed for the synthesis of 2,3‐disubstituted benzofuran derivatives. This cascade reaction sequence involves intermolecular carbopalladation and C(sp3)−H functionalization followed by isomerization.
A catalytic asymmetric allylic alkylation reaction of 3‐aryloxindoles was accomplished via a dual catalysis merging palladium catalysis and asymmetric H‐bonding catalysis for the first time. Using this approach, allylated oxindoles bearing chiral all‐carbon quaternary centers were produced in high yields with good enantioselectivities (up to 92 % yield and 96:4 er).
An efficient copper(I) iodide‐catalyzed sulfenylation of maleimides and related 3‐indolylmaleimides with thiols has been developed in the presence of fluoroboric acid. Several 3‐thiomaleimides and 3‐indolyl‐4‐thiomaleimides were obtained with good yields under ligand‐free conditions. The methods are simple, practical and show good functional group tolerance.
A copper(I)‐catalyzed addition of alkylborane reagents to α‐iminoacetates has been developed to assemble both acyclic and cyclic α‐branched α‐amino carboxylic acid derivatives in good yields. A wide variety of unactivated alkenes are well tolerated in this transformation.
The copper‐catalyzed reaction of 5‐substituted penta‐1,4‐diyn‐3‐yl acetates with P(O)H compounds to efficiently give a new class of phosphonyl diynes is reported. The reaction may take place through a regioselective nucleophilic attack of phosphorus nucleophiles on Cu‐allenylidene intermediates to form allenyl intermediates followed by a rapid allene‐alkyne isomerization process. The synthetic utility of the obtained products is demonstrated.
An efficient asymmetric synthesis of spirocyclohexenone β‐lactams bearing three contiguous stereocenters has been achieved in moderate to good yields and high stereoselectivities. The protocol involves the combination of a squaramide‐catalyzed sulfa‐Michael addition under desymmetrization via a dynamic kinetic resolution of racemic 2,5‐cyclohexadienones.
A novel one‐pot reaction which combines halogenation, decarboxylation/desulfonamidation with oxidation has been developed. Diverse valuable 3,3‐dihalo‐2‐oxindole compounds can be produced rapidly and safely with isolated yields of up to 98% under mild conditions.
Cobalt‐catalyzed C−H amination of arenes with alkylamines by the assistance of 8‐aminoquinoline as auxiliary through sp2 C−H bond functionalization has been achieved. Attractive features of this protocol include the low loading of the cobalt catalyst and the readily available reagents.
N‐Alkenylated triazolinone ylides were generated through copper‐catalyzed oxy‐N‐alkenylation of triazolopyridines. The mechanistic course of this aerobic tandem reaction has been experimentally elucidated and primary photophysical data of the ylide products are also given.
A new protocol for the direct reductive cobalt‐catalyzed arylation of benzyl chlorides has been developed in order to form functionalized diarylmethanes. A variety of reactive groups either on the aryl or the benzyl halide was employed. This represents the first cobalt‐catalyzed reductive cross‐coupling which does not require any ligand and pyridine. A reaction pathway is proposed involving a radical benzyl species.
A stereocontrolled [4+1] annulation of α‐hydroxycyclobutenones has been disclosed. For the first time, α‐hydroxycyclobutenones have been proven as facile diene precursors for [4+1] annulation. Meanwhile, the reported transformation presents a concise synthetic route to polysubstituted cyclopentenones with high stereoselectivity.
