A highly efficient chiral N,N′‐dioxide‐zinc(II) complex catalytic system has been developed for the enantioselective aza‐Friedel–Crafts reaction of isatin‐derived ketimines with indoles. A series of enantiomerically enriched 3‐indolyl‐3‐aminooxindoles containing a tetrasubstituted stereocenter were obtained in up to 99% yield with up to 96% ee. Furthermore, control experiments provide a fundamental sight into the mechanism of the reaction.
An efficient ligand‐free copper‐manganese (Cu‐Mn) spinel oxide‐catalyzed direct tandem C−H oxygenation and N‐arylation of benzylamines has been developed. The method has been utilized for the synthesis of medicinally important 2‐arylquinazolin‐4(3H)‐ones. Salient features of this method include recyclable catalyst, no ligand, excellent product yields, shorter reaction times and a broad substrate scope.
Several chiral BINOL‐derived bisoxazoline (BOX)/copper(II) complexes were synthesized and evaluated as catalysts for the Friedel–Crafts reaction of indoles with isatin‐derived β,γ‐unsaturated α‐keto esters. The resulting bis‐indole products bearing a quaternary stereocenter were obtained in excellent yields and enantioselectivities. Additionally, the desired products were practically transformed to α‐amino esters, α‐hydroxy esters and α‐keto amides. It is noteworthy that this catalytic procedure was conducted with a catalyst loading of 0.5 mol% without any discernible decrease in the reactivity or enantioselectivity.
2,2‐Difluoro‐1,3‐diketones are introduced as gem‐difluoroenolate precursors for the first example of an organocatalytic asymmetric aldol addition with N‐benzylisatins to form 3‐difluoroalkyl‐3‐hydroxyoxindoles.
A direct access to multisubstituted 1,3‐dienes by α‐exclusive alkylidenation of crotonic derivatives has been developed. This protocol, mediated by titanium tetrachloride chelation, features excellent regio‐ and stereoselectivity, mild reaction conditions, easy operation and wide substrate scope. Conversions of the derived dienes to other useful molecules were also explored.
A catalyst‐controlled regiodivergent dehydrogenative Heck reaction of 4‐arylthiophene/furan‐3‐carboxylates has been realized. Use of a palladium catalyst led to the C‐5 alkenylation through electronic palladation, while a ruthenium catalyst favored the C‐2 alkenylation with the assistance of a directing group. This reaction exhibited good to excellent regioselectivities.
An efficient, metal‐free, silicon–hydrogen bond functionalization based on the microwave‐assisted reaction of readily available enynones and silanes is reported. This process seemingly proceeds through a 2‐furyl carbene species, a particularly elusive intermediate. Preliminary studies on the metal‐free oxygen–hydrogen and nitrogen–hydrogen bond functionalization of representative alcohols, azoles and sulfonamides are also provided.
The first copper(I)‐catalyzed asymmetric 1,3‐dipolar [3+4] cycloaddition of nitrones with azoalkenes has been developed, affording a variety of biologically important 1,2,4,5‐oxatriazepane derivatives in good yields with exclusive regioselectivities and excellent enantioselectivities.
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.
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.
A user‐friendly, calcium(II)‐ and copper(II)‐catalyzed one‐pot reaction sequence to furnish cyclopenta[b ]pyrroles with a high level of complexity is depicted. The reaction involves the following sequential transformations: (i) an aza‐Piancatelli cyclization, (ii) a hydroamination/isomerization process and (iii) a subsequent Friedel–Crafts‐type reaction to afford the desired compounds from readily available 2‐furylcarbinols, anilines and secondary alcohols with a minimum of precautions.
A new synthetic method for α‐alkynyl‐α,β‐unsaturated esters is presented herein. The method is based on a copper(I)‐catalyzed three‐component reaction of a terminal alkyne, diazoesters and aldehydes. The reaction is featured by mild conditions, high yields and excellent stereoselectivity. Cu(I) carbene migratory insertion is proposed as the key step in the transformation.
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 regio‐ and stereoselective method for the synthesis of (E)‐α,β‐unsaturated carbonyls has been developed via a silver‐catalyzed tandem epoxide rearrangement/intermolecular carbonyl‐heteroalkyne metathesis. Various heteroalkynes including ynol ethers, ynamides, and thioalkynes work well for this transformation, leading to the production of (E)‐α,β‐unsaturated esters, amides, and thioesters in moderate to excellent yields with good functional group compatibility. It represents one of the rare examples of regio‐ and stereoselective intermolecular alkyne‐carbonyl metathesis (ACM).
The first highly enantioselective intramolecular N−H bond insertion was realized by using copper catalysts modified with chiral spirobisoxazoline ligands, which provides a novel strategy for the synthesis of chiral 2‐carboxytetrahydroquinolines. This reaction features fast reaction rate, high yield, high enantioselectivity, and mild reaction conditions.
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.
We report a radical cation [4+2] annulation of arylalkenes to afford naphthalene derivatives using an organic photosensitizer (9‐mesityl‐10‐methylacridinium perchlorate) under visible light photocatalysis. In the presence of oxygen (in the air), the oxidative dimerization/intramolecular [4+2] cycloaddition of two alkene molecules provides 3,4‐dihydronaphthalen‐1(2H)‐ones in good to high yields. Under a nitrogen atmosphere, (dihydro)naphthalenes were attained in moderate to excellent yields by using Selectfluor as the oxidant. The transformation proceeds via a tandem dimeric electrophilic addition/Friedel–Crafts cyclization/radical coupling/elimination sequence. This approach represents a mild and straightforward assembly of the naphthalene skeleton using a visible light photocatalytic cascade strategy.
A regio‐ and enantioselective copper‐catalyzed 1,4‐conjugate addition of trimethylaluminium to linear δ‐aryl‐substituted α,β,γ,δ‐unsaturated alkyl ketones was developed. A series of γ,δ‐unsaturated alkyl ketones were obtained in good yields with high regio‐ and enantioselectivity (up to 88% ee and 96:4 dr). Expansion of the reaction scope to substrates containing aromatic heterocycles also afforded good yields and enantioselectivities (up to 91% ee) with very high regioselectivities, exclusively providing the single 1,4‐products.
