A copper(I)‐catalysed domino transformation for the synthesis of tricyclic imidazobenzimidazole derivatives was developed. Using readily available primary propargylic amines and o‐haloarylcarbodiimides as the starting materials, a variety of substituted benzo[d]imidazo[1,2‐a]imidazoles was efficiently and selectively assembled. Further investigations indicated that the domino reaction was likely the result of a novel addition/cycloisomerisation/coupling process.
The selective copper‐catalyzed borylation of silylalkynes in the presence of a diboron reagent and methanol produced a variety of (Z)‐β‐(borylvinyl)silanes. The appropriate use of a selective ligand for copper allows the chemo‐, regio‐, and stereoselective monoborylation of silylalkynes. The β‐regioselectivity of an N‐heterocyclic carbene (NHC)‐copper catalyst was investigated by DFT calculations.
Metal triflate‐catalysed intermolecular Friedel–Crafts reactions involving electron‐rich benzenoid arenes and spiroepoxyoxindoles at the spiro‐centre have been developed for the exclusive regioselective synthesis of 3‐aryl‐(3‐hydroxymethyl)oxindoles with an all‐carbon quaternary centre. Selective ring opening of spiroepoxyoxindoles with phenols provided a direct access to 3‐(hydroxymethyl)‐3‐(2‐hydroxyaryl)oxindoles. We have utilized this methodology successfully as the key step for the synthesis of benzofuroindolines and 2H‐spiro[benzofuran]‐3,3′‐oxindoles.
New 3rd generation designer ansa‐ruthenium(II) complexes featuring N,C‐alkylene‐tethered N,N‐dialkylsulfamoyl‐DPEN/η6‐arene ligands, exhibited good catalytic performance in the asymmetric transfer hydrogenation (ATH) of various classes of (het)aryl ketones in formic acid/triethylamine mixture. In particular, benzo‐fused cyclic ketones furnished 98 to >99.9% ee using a low catalyst loading.
A new transition metal‐free oxidative coupling of unactivated terminal alkenes with aldehydes and hydroperoxides in the presence of 10 mol% potassium tert‐butanolate (t‐BuOK) is described thereby realizing trifunctionalization of alkenes toward 2,3‐epoxy ketones. This method is applicable to a wide range of aldehydes, including aryl and alkyl aldehydes, with excellent functional group tolerance, and provides for the one‐step assembly of 2,3‐epoxy ketones.
We report the Heck cross‐coupling of notoriously unreactive, but synthetically valuable olefins: vinyl sulfoxides, vinyl sulfones, and vinyl sulfides. Key findings include the importance of the sterically hindered (tri‐tert‐butyl)phosphine ligand and the unique effectiveness of triethylamine as the base. The method is general, E‐selective, and can be used to synthesize disubstituted or trisubstituted olefins through simple adjustments of stoichiometry.
The regioselective direct 3‐arylation of indoles with 1‐diazonaphthalen‐2‐(1H)‐ones was developed by means of a rhodium(II) pivalate‐catalyzed cross‐coupling reaction. This procedure provided a variety of novel 3‐naphthylindoles in high yield. The direct coupling of benzofuran, pyrrole or furan with 1‐diazonaphthalen‐2‐(1H)‐ones afforded 2‐ or 3‐naphthyl substituted heterocycles.
A new, non‐symmetrical copper(II) pincer complex catalyzes much more efficiently the formation of benzofuran by the reaction between ortho‐iodophenols and alkynes. The lowest catalyst loadings are realized for this reaction, and bromo‐ and chlorophenols are heteroannulated for the first time. Strong evidence for hydrophenoxylation and intramolecular halogen atom‐transfer steps catalyzed by this remarkably active, recyclable homogeneous catalyst is provided.
A cationic gold(I)‐catalyzed decarboxylative etherification of propargyl carbonates to selectively produce propargyl ethers is reported. In the reaction the gold(I) catalyst shows a distinct σ‐Lewis acidity rather than the commonly observed π‐Lewis acidity, and thus catalyzes the decarboxylation of a variety of propargyl carbonates to give the corresponding propargyl ethers with high selectivity. This reaction represents a rare example of the tunable reactivity of cationic gold(I) complexes between σ‐Lewis acidity and π‐Lewis acidity.
An efficient method for the synthesis of 3‐alkylated indoles is described. The oxidative cross‐coupling reaction of diphenylmethane derivatives with indoles at the C‐3 position was achieved employing the N,N‐dimethylcarbamoyl moiety as an auxiliary group in the presence of iron(II) chloride (FeCl2) and 2,3‐dichloro‐5,6‐dicyanoquinone (DDQ).
A convenient palladium‐catalyzed tandem reaction of aryl iodides and salicyl N‐tosylhydrazones has been achieved to afford a series of compounds containing the novel spiro[benzofuran‐3,2′‐chromene] scaffold in moderate to good yields. This efficient catalytic reaction, which tolerates various functional groups, combines alkyne‐based 5‐exo‐dig cyclization, palladium(II) carbene migratory insertion and intramolecular cyclization, generating three new bonds in one reaction.
An efficient and concise one‐pot strategy for the direct alkylation of quinoline N‐oxides via palladium‐catalyzed dual C H bonds activation has been developed. This methodology provides quinoline‐containing heterocyclic molecules in moderate to excellent yields.
The rhodium‐catalyzed selective cyanation of C H bonds of indolines and indoles with N‐cyano‐N‐phenyl‐para‐methylbenzenesulfonamide is described. This protocol offers a facile access to C‐7 cyanated indolines and C‐2 cyanated indoles with high site selectivity and excellent functional group tolerance.
Imino‐/enaminophosphonates derived from amines and diethyl phenacyl phosphonates undergo oxidative cyclization via C H bond activation catalyzed by palladium chloride to provide a convenient route for the synthesis of substituted indol‐3‐yl and pyrrol‐3‐yl phosphonates.
The first enantioselective Friedel–Crafts alkylation of indoles and pyrroles with 3‐hydroxy‐3‐indolyloxindoles to access two novel types of 3,3‐diaryloxindoles catalyzed by chiral imidodiphosphoric acids has been reported. A range of quaternary carbon centered 3,3‐diaryloxindoles were synthesized in high yield (up to >99%) with excellent enantioselectivity (up to 98% ee) at low catalyst loadings (as low as 0.5 mol%). The Friedel–Crafts reaction between indoles and 3‐hydroxy‐3‐indolyloxindoles is amenable to gram scale syntheses.
A metal‐free C C bond formation method via the oxidative cross‐coupling reaction of isochroman and indole derivatives was established. Various α‐fuctionalized cyclic ethers were achieved in satisfactory yields using di‐tert‐butyl peroxide (DTBP) as the oxidant. This method is also a potentially efficient strategy for the construction of cyclic ether‐containing targets.
