An inherently chiral C3‐symmetric triaminotribenzotriquinacene was condensed in racemic and enantiomerically pure form with a bis(salicylaldehyde) to form 2+3 salicylimine cage compounds. ...Investigations on the chiral self‐sorting revealed that while entropy favors narcissistic self‐sorting in solution, selective social self‐sorting can be achieved by exploiting the difference in solubility between the homochiral and heterochiral cages. Gas sorption measurements further showed that seemingly small structural differences can have a significant impact on the surface area of microporous covalent cage compounds.
Sorted out: An inherently chiral C3‐symmetric triaminotribenzotriquinacene was condensed in racemic and enantiomerically pure form with a bis(salicylaldehyde) to form 2+3 salicylimine cage compounds. Investigations revealed that entropy favors narcissistic self‐sorting in solution, and selective social self‐sorting can be achieved by exploiting the difference in solubility between the homochiral and heterochiral cages.
A contorted polycyclic aromatic hydrocarbon (PAH) in the shape of a monkey saddle has been synthesized in three steps from a readily available truxene precursor. The monkey saddle PAH is consisting ...of three five‐, seven six‐, and three eight‐membered rings and has been unambiguously characterized by single‐crystal X‐ray diffraction. Owing to the three biaryl axes the monkey saddle PAH is inherently chiral. The inversion of the two enantiomeric structures into each other preferably occurs through a twisting of peripheral rings rather than by a fully planar intermediate, as has been calculated by DFT methods. Enantiomers were separated by chiral HPLC and inversion barriers determined by variable temperature circular dichroism spectroscopy, supporting the twisting mechanism.
Based on a truxene a chiral monkey saddle shaped polyaromatic hydrocarbon (PAH) with three eight‐membered rings was accessible in only three synthetic steps. The enantiomers were separated by chiral HPLC and investigated photophysically.
The strategy of chirality‐assisted synthesis, which makes use of enantiomerically pure building blocks that are designed to associate in a single geometric orientation, was applied to synthesize an ...octameric hydrogen‐bonded capsule with a cavity volume of 2300 Å3. This cube‐shaped capsule forms even host–guest complexes with tetraalkylammonium ions, and accommodates the large tetrahexadecylammonium cation in its cavity. The use of an enantiopure building block was shown to be highly beneficial for capsule formation, whereas its racemate also generates a large amount of ill‐defined aggregates in solution and crystallizes as a hydrogen‐bonded network.
Take the enantiopure and you will succeed: An octameric molecular capsule assembled through hydrogen bonds was synthesized by the strategy of chirality‐assisted synthesis. Both ionic and neutral guests can be encapsulated within its 2300 Å3 cavity volume. The racemic starting material led to a mixture that also contained oligomeric and polymeric species.
At room temperature under mild photochemical conditions, namely irradiation with a simple blue light LED, gold(i) chloro complexes of both phosphane and carbene ligands in combination with ...aryldiazonium salts afford arylgold(iii) complexes. With chelating P,N-ligands cationic six- or five-membered chelate complexes were isolated in the form of salts with weakly coordinating counter anions that were brought in from the diazonium salt. With monodentate P ligands or N-heterocyclic carbene ligands and diazonium chlorides neutral arylgold(iii) dichloro complexes were obtained. The coordination geometry was determined by X-ray crystal structure analyses of representative compounds, a cis arrangement of the aryl and the phosphane ligand at the square planar gold(iii) center is observed.
The first gold‐catalyzed photoredox C(sp2)−H difluoroalkylation and perfluoroalkylation of hydrazones with readily available RF−Br reagents is reported. The resulting gem‐difluoromethylated and ...perfluoroalkylated hydrazones are highly functionalized, versatile molecules. A mild reduction of the coupling products can efficiently produce gem‐difluoromethylated β‐amino phosphonic acids and β‐amino acid derivatives. In mechanistic studies, a difluoroalkyl radical intermediate was detected by an EPR spin‐trapping experiment, indicating that a gold‐catalyzed radical pathway is operating.
The radical C−H fluoroalkylation of hydrazones in the presence of a gold photoredox catalyst is compatible with a broad range of functional groups and provides access to E‐configured products that can be converted into useful synthetic building blocks. A radical intermediate was trapped and analyzed by EPR spectroscopy.
A gold‐catalyzed cascade annulation of propargylic silyl ethers with anthranils proceeds through a sequential ring opening/1,2‐H‐shift/protodeauration/Mukaiyama aldol cyclization. This method offers ...a regiospecific and modular access to 2‐aminoquinolines and other quinoline derivatives under mild conditions and with a broad functional‐group tolerance. The conversion is possible on a gram scale, which underlines the synthetic practicability of this methodology. The versatility of the obtained scaffold has been demonstrated by useful postfunctionalization.
All together now: A gold‐catalyzed cascade annulation of propargylic silyl ethers with anthranils proceeds through a sequential ring opening/1,2‐H‐shift/protodeauration/Mukaiyama aldol cyclization. This method offers regiospecific and modular access to 2‐aminoquinolines and other quinoline derivatives under mild conditions and with a broad functional‐group tolerance.
An unprecedented and challenging radical–radical cross‐coupling of α‐aminoalkyl radicals with monofluoroalkenyl radicals derived from gem‐difluoroalkenes was achieved. This first example of tandem ...C(sp3)−H and C(sp2)−F bond functionalization through visible‐light photoredox catalysis offers a facile and flexible access to privileged tetrasubstituted monofluoroalkenes under very mild reaction conditions. The striking features of this redox‐neutral method in terms of scope, functional‐group tolerance, and regioselectivity are illustrated by the late‐stage fluoroalkenylation of complex molecular architectures such as bioactive (+)‐diltiazem, rosiglitazone, dihydroartemisinin, oleanic acid, and androsterone derivatives, which represent important new α‐amino C−H monofluoroalkenylations.
Privileged products: An α‐C(sp3)−H monofluoroalkenylation of unactivated tertiary amines through a mild, efficient, and redox‐neutral route delivers privileged tetrasubstituted monofluoroalkenes under photoredox catalysis through the radical–radical cross‐coupling of α‐aminoalkyl radicals with monofluoroalkenyl radicals. This method enables the challenging late‐stage monofluoroalkenylation of complex molecules.
A facile, site‐selective, and divergent approach to construct 2‐aminopyrroles and quinoline‐fused polyazaheterocycles enabled by a simple gold(III) catalyst from ynamides and anthranils under mild ...reaction conditions is described. This one‐pot strategy uses readily available starting materials, proceeds in a highly step‐ and atom‐economical manner, with broad substrate scope and scale‐up potential. The key element for success in this tandem reaction is a catalyst‐directed preferred quenching of the in situ generated gold carbene intermediates by a nucleophilic benzyl/2‐furylmethyl moiety on the ynamides as an alternative to the known C−H annulation leading to indoles.
One‐pot strategy: A simple gold(III) catalyst enables the construction of 2‐aminopyrroles and quinoline‐fused polyazaheterocycles from ynamides and anthranils under mild reaction conditions. This strategy uses readily available starting materials, proceeds in a highly step‐ and atom‐economical manner, with broad substrate scope and scale‐up potential.
We herein report the unprecedented synthesis of diverse biologically important aza‐heterocycles by employing sulfilimines as nitrene transfer reagents. This class of sulfur‐based aza‐ylides had not ...been successfully used for gold nitrene transfer before. This work contains an efficient generation of α‐imino gold carbenes by N−S cleavage of sulfilimines. These gold carbenes undergo C−H insertion, cyclopropanation, and nucleophilic attack to form indoles (44 examples), 3‐azabicyclo3.1.0hexan‐2‐imines (24 examples), and imidazoles (3 examples). Our study represents a unique gold‐catalyzed reaction between alkynes and sulfur ylides, and also includes the first aza‐heterocycle synthesis that proceeds by intermolecular nitrene transfer followed by cyclopropanation of the α‐imino gold carbenes. Moreover, an unexpected synthesis of 4‐acylquinolines (3 examples) from 2‐acylphenyl sulfilimines and propargylic silyl ether derivatives by a 1,2‐hydride shift onto the α‐imino gold carbene and a subsequent Mukaiyama aldol cyclization was discovered.
Golden diversity: Readily available sulfilimines were successfully applied as versatile nitrene transfer reagents. By trapping the resulting α‐imino gold carbenes with divergent functionalities, four different types of aza‐heterocycles (indoles, 3‐azabicyclo3.1.0hexan‐2‐imines, quinolines, and imidazoles) were prepared in high efficiency.
Terminal 1,2-dialkynylarenes undergo an unexpected cyclization hydroarylation reaction toward naphthalene derivatives in benzene as the solvent. The regioselectivity of the reaction can be controlled ...by careful catalyst tuning. Also, the preparation of a bench-stable cationic amine complex or simple heterogenization of the catalyst on neutral aluminum oxide, which enables efficient catalyst recycling, was possible. Intensive mechanistic investigations were undertaken, giving new insights into the so-far underestimated role of acetylides in gold chemistry. The gold plays a fascinating dual role serving to both catalyze the reaction and activate the substrate by Au–C-σ bond formation. Evidence of gem-diaurated compounds playing an important part for gold catalysis is also reported.
PDF
