Catalyst-Driven Scaffold Diversity: Selective Synthesis of Spirocycles, Carbazoles and Quinolines from Indolyl Ynones

Highly Diastereo- and Enantioselective Synthesis of Quinuclidine Derivatives by an Iridium-Catalyzed Intramolecular Allylic Dearomatization Reaction

Asymmetric construction of quinuclidine derivatives has been realized by an iridium-catalyzed allylic dearomatization reaction. The catalytic system, derived from [Ir(cod)Cl] 2 and the Feringa ligand, tolerates a broad range of substrates. A large array of quinuclidine derivatives can be obtained under mild conditions in good to excellent yields (68%–96%), diastereoselectivity (up to >20/1 dr), and enantioselectivity (up to >99% ee). These products feature versatile functional group diversity and can undergo diverse transformations. A model that accounts for the origin of the stereoselectivity has been proposed based on density functional theory (DFT) calculations.

Gold catalysed transformation of 2-arylindoles to terphenyl amines via 3-dienyl indoles and Brønsted acid promoted formation of 2-carboxyindoles to 3-indenylindoles via 3-allenylindoles

Gold-catalysed intramolecular reaction of unprotected/protected 3-dienyl indoles leads to the formation of functionalised terphenylamines with high efficiency; this reaction can also be accomplished in one pot by starting with 2-arylindole and propargylic alcohols. This reaction occurs via 3-dienyl indoles and proceeds likely by gold-catalysed cascade cyclisation, aromatisation and fragmentation of the indole heterocyclic moiety. We have also found that PTSA can work well giving comparable yields, but at least one mole equivalent of PTSA is required. On the other hand, 3-indenylindoles have been synthesised from indole-2-carboxylates (2-carboxyindoles) and propargylic alcohols through Brønsted acid mediation. Many of these indenylindoles exhibit isomerism (probably diastereomers) in the solution state (1H NMR). Two examples of indolo-indenyl acetates have been prepared by reacting the above terphenylanilines with PhI(OAc)2. Key products are characterised by X-ray crystallography.

Synthesis of 4-(1H-isochromen-1-yl)isoquinolines through the silver-catalysed homodimerization of ortho-alkynylarylaldehydes and subsequent condensation of the 1,5-dicarbonyl motif with NH3

4-(1H-Isochromen-1-yl)isoquinoline derivatives were synthesized in high yields via the AgBF₄-catalyzed self-reaction of ortho-alkynylarylaldehydes to give isochromene intermediates, followed by the dehydration of the 1,5-dicarbonyl motif with NH₃. Compared with electron-rich aromatic substituents, this strategy can provide the desired isochromene products with an electron-deficient isoquinoline unit. The reactions feature simple experimental operations, mild reaction conditions and high product yields.

We demonstrate a strategy that can provide isochromenes with an electron-deficient isoquinoline unit. The reactions feature simple operations, mild conditions and high yields.

Unexpected formation and conversion: role of substituents of 1,3-ynones in the reactivity and product distribution during their reactions with Ru3(CO)12

Electronic and steric effects of the substituents in 1,3-ynones play key roles in the product distribution and molecular structures.

Synthesis of 3-Substituted 3-Bromo-1-phenylallenes from Alkynylcycloheptatrienes

A new method has been developed for the preparation of 3-bromo-1-phenylallenes from 7-alkynylcycloheptatrienes and N-bromosuccinimide. Trisubstituted bromoallenes were obtained at room temperature in moderate to excellent yields. Functionalization of the carbon-bromine bond via Pd- or Cu-catalyzed cross-coupling reactions easily provided substituted allenes.

Synthesis of Structurally Diverse N-Substituted Quaternary-Carbon-Containing Small Molecules from α,α-Disubstituted Propargyl Amino Esters

N-containing quaternary stereocenters represent important motifs in medicinal chemistry. However, due to their inherently sterically hindered nature, they remain underrepresented in small molecule screening collections. As such, the development of synthetic routes to generate small molecules that incorporate this particular feature are highly desirable. Herein, we describe the diversity-oriented synthesis (DOS) of a diverse collection of structurally distinct small molecules featuring this three-dimensional (3D) motif. The subsequent derivatisation and the stereoselective synthesis exemplified the versatility of this strategy for drug discovery and library enrichment. Chemoinformatic analysis revealed the enhanced sp3 character of the target library and demonstrated that it represents an attractive collection of biologically diverse small molecules with high scaffold diversity.

Dearomatizing Spiroannulation Reagents: Direct Access to Spirocycles from Indoles and Dihalides

Unfunctionalized indoles can be directly converted into 3,3'-spirocyclic indolenines and indolines upon reaction with electrophilic dihalides in the presence of t-BuOK/BEt₃. This double C-C bond forming reaction, which simultaneously generates a quaternary spirocyclic center, typically proceeds in high yield and has good functional group tolerance. In contrast to existing dearomatizing spirocyclization approaches, there is no need to prepare a prefunctionalized aromatic precursor, enabling faster access to valuable spirocyclic products from simple, commercially available aromatics in one step.

Scaffold Diversity Synthesis Delivers Complex, Structurally, and Functionally Distinct Tetracyclic Benzopyrones

Complexity-generating chemical transformations that afford novel molecular scaffolds enriched in sp3 character are highly desired. Here, we present a highly stereoselective scaffold diversity synthesis approach that utilizes cascade double-annulation reactions of diverse pairs of zwitterionic and non-zwitterionic partners with 3-formylchromones to generate highly complex tetracyclic benzopyrones. Each pair of annulation partners adds to the common chroman-4-one scaffold to build two new rings, supporting up to four contiguous chiral centers that include an all-carbon quaternary center. Differently ring-fused benzopyrones display different biological activities, thus demonstrating their immense potential in medicinal chemistry and chemical biology research.

Gold-Catalyzed Synthesis of 2-Sulfenylspiroindolenines via Spirocyclizations

2-Phenylsulfenyl-N-propargyl tryptamines have been prepared by electrophilic sulfuration of the corresponding tryptamines. These compounds undergo gold-catalyzed spirocyclizations to the corresponding 2-phenylthiospiroindolenines in good yields. The compounds were analyzed by NMR experiments, infrared, mass spectra and X-ray diffraction. This method provides a new efficient entry to the synthesis of 2-sulfenyl spiroindolic compounds.

Synthesis of spiroindolenines by intramolecular ipso-iodocyclization of indol ynones

A high-yielding fast spirocyclization of easily available indol ynones has been developed by applying N-iodosuccinimide.

Photoredox-catalyzed procedure for carbamoyl radical generation: 3,4-dihydroquinolin-2-one and quinolin-2-one synthesis

A reductive approach for carbamoyl radical generation from N-hydroxyphthalimido oxamides under photoredox catalysis is outlined. This strategy was applied to the synthesis of 3,4-dihydroquinolin-2-ones via the intermolecular addition/cyclization of carbamoyl radicals with electron deficient olefins in a mild, redox-neutral manner. Under a general set of reaction conditions, diversely substituted 3,4-dihydroquinolin-2-ones, including spirocyclic systems can be prepared. By using chlorine-substituted olefins, aromatic quinolin-2-ones can also be accessed.

Substrate-Controlled Product Divergence: Silver-Catalyzed Reaction of Trifluoromethyl Ketones with Terminal Alkynes

A distinct dichotomy in product distribution was initially observed in the silver-catalyzed reaction of trifluoromethyl (CF₃) ketones with terminal alkynes having two different types of electronic natures. The domino reaction smoothly proceeded almost exclusively with high stereoselectivity with terminal alkynes containing ester groups, whereas alkynylation occurred in good yield when terminal alkynes containing aryl or alkyl groups were present. The results indicated that the electronic nature of terminal alkynes can act as a switch that enables either the domino reaction or alkynylation between terminal alkynes and CF₃ ketones.

Temperature switchable Brønsted acid-promoted selective syntheses of spiro-indolenines and quinolines

A high-yielding, temperature switchable divergent approach towards the synthesis of either spiro-indolenines or quinolines is described, starting from easily available indolyl ynones.

Selective synthesis of three product classes from imine and carboxylic acid precursors via direct imine acylation

Three divergent procedures allow the selective generation of δ-lactams, β-lactams and tetrahydropyrimidinones from common imine and carboxylic acid precursors.

Dearomatisation approaches to spirocyclic dienones via the electrophilic activation of alkynes

Two simple metal-mediated dearomatising spirocyclisation protocols to generate spirocyclic dienones from anisole and phenol-tethered ynones in high yields are described.

Structurally Divergent Lithium Catalyzed Friedel-Crafts Reactions on Oxetan-3-ols: Synthesis of 3,3-Diaryloxetanes and 2,3-Dihydrobenzofurans

The first examples of 3,3-diaryloxetanes are prepared in a lithium-catalyzed and substrate dependent divergent Friedel-Crafts reaction. para-Selective Friedel-Crafts reactions of phenols using oxetan-3-ols afford 3,3-diaryloxetanes by displacement of the hydroxy group. These constitute new isosteres for benzophenones and diarylmethanes. Conversely, ortho-selective Friedel-Crafts reactions of phenols afford 3-aryl-3-hydroxymethyl-dihydrobenzofurans by tandem alkylation-ring-opening reactions; the outcome of the reaction diverging to structurally distinct products dependent on the substrate regioselectivity. Further reactivity of the oxetane products is demonstrated, suitable for incorporation into drug discovery efforts.