An asymmetric total synthesis of ent‐ancistrocladinium A was developed via chiral phosphoric acid‐catalyzed asymmetric reductive amination of 1‐aryl‐2‐propanone and naphthylamine followed by a Bischler–Napieralski reaction. Direct use of the naphthyl moiety in the amine as a key building block in the natural product allowed us to achieve the total synthesis of ancistrocladinium A in only three steps from the known starting materials.
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.
By the design of suitable starting materials, a silver(I)‐catalyzed epoxide ring‐opening/1,2‐acyl migration/cyclization cascade has been developed, which allowed us to systematically prepare unsymmetrical 3‐formylfurans. Various 3‐formylfurans were prepared in good to excellent yields. In addition, the distinct fluorescence properties of 3‐formylfurans in solution and the solid state are disclosed.
Chiral 1,2‐diamines are privileged structural motifs in organocatalysis, whereas efficient 1,3‐diamine‐derived organocatalysts are very rare. Herein we report a highly efficient camphor‐1,3‐diamine‐derived squaramide organocatalyst. Its catalytic activity in Michael additions of 1,3‐dicarbonyl nucleophiles to trans‐β‐nitrostyrene derivatives provides excellent enantioselectivities (up to >99% ee).
A rotor‐stator homogenizer was found to be an effective mixing tool that accelerated solid‐liquid phase‐transfer reactions. In the asymmetric alkylation under phase‐transfer conditions using the homogenizer, a considerably high turnover frequency was observed.
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.
A novel iron‐catalyzed direct alkylamination reaction of phenols has been achieved with O‐benzoyl‐N‐alkylhydroxylamines as aminating agents. This protocol provides a facile access to N‐alkyl‐substituted aminophenols though a radical reaction from phenols. The catalytic direct alkylamination operates at room temperature without the need of any ligands and additives to afford the desired products with excellent regioselectivity and functional group tolerance.
A copper‐catalyzed new domino reaction allowed the facile and direct construction of the dibenzo‐fused azepinone ring leading to an array of novel small molecules. The co‐catalyst, ligand or additive free one‐pot method afforded a unique class of functionalized derivatives, one of which showed encouraging PDE4 inhibition in vitro and apoptosis in vivo.
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.
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.
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).
Catalyzed by a Cinchona‐based thiourea, the [3+2] cycloadditions of barbiturate‐based olefins with 3‐isothiocyanatooxindoles proceeded readily, and furnished dispirobarbiturates in excellent chemical yields with excellent diastereo‐ and enantioselectivities. The absolute configuration of dispirobarbiturates was firmly confirmed by an X‐ray single crystal structure analysis. A reaction mechanism was proposed to account for the enantioselective formation of dispirobarbiturates.
Aluminum(III) complexes derived from aminotriphenolate ligands are shown to be excellent catalysts for the formation of cyclic sulfites from a range of (functionalized) terminal and internal epoxides, and ex situ generated sulfur dioxide. The developed catalytic protocol is characterized by its operational simplicity, wide scope in epoxide reaction partners, good to excellent isolated yields and mild reaction conditions [50–70 °C, p(SO2) <1 bar]. The synthetic potential of these cyclic sulfites in organic synthesis is demonstrated in the preparation of N‐substituted aziridines through a three‐step protocol.
The copper(II)‐catalyzed decarboxylative coupling reactions of arylglyoxylic acids with isatins afford 4H‐benzo[d][1,3]oxazin‐4‐ones via decarbonylation and concurrent C–N, C–O bond formation.
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 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 unprecedented copper(II)‐catalyzed enantioselective 1,3‐dipolar [3+4] cycloaddition of azomethine imines with in situ formed azoalkenes has been realized. This strategy provides a facile access to biologically important 1,2,4,5‐tetrazepine derivatives in high yield with exclusive regioselectivity and high stereoselectivity. Moreover, enantioenriched azomethine imines could be obtained via an efficient kinetic resolution using the same approach.
Enantiomerically pure diarylmethylamines are important building blocks in active pharmaceutical ingredients. Herein, we report a rhodium precatalyst with a chiral disulfoxide ligand that effects the 1,2‐addition of arylboroxines to aromatic imines to give high yields and high enantioselectivities of these products. The present paper describes a system that is very simple, where the ease of synthesis of the chiral ligand is combined with low catalyst loadings and reaction conditions that do not need any additives or external base.
A simple alkylamine [(iPr)2NEt] has been used to activate an air‐ and moisture‐stable iron(II) pre‐catalyst for alkene and alkyne hydrofunctionalization reactions. This amine activation has enabled the highly operationally simple hydrosilylation and hydroboration of alkenes and alkynes using just 0.25–2 mol% iron catalyst and 1–25 mol% amine. Significantly, these reactions proceed in equal yield under both air and inert reaction conditions.
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.
