Solvent-Regulated Coupling of 2-Alkynylbenzaldehydes with Cyclic Amines: Selective Synthesis of Fused N-Heterocycles and Functionalized Naphthalene Derivatives

Access to Polyheterocyclic Compounds through Iron(II)-Mediated Radical Cascade Cyclization Utilizing 2-Ethynylbenzaldehydes and Aryl Isonitriles

An oxidative radical cascade addition cyclization approach for the synthesis of quinoline-based π-extended polyheterocyclic compounds is reported. Eco-friendly iron catalysis and inexpensive tert-butylhydroperoxide (TBHP) as the oxidant have been utilized in the transformation of various readily available ortho-alkynylated aromatic aldehydes as radical precursors with aryl isonitriles as radical acceptors. Indole and thiophene-based carbaldehydes allow the preparation of quinolines that are π-conjugated with an additional heteroarene moiety in a single sequence by applying the introduced method.

Oxoammonium salt-promoted diverse functionalization of saturated cyclic amines with dinucleophiles

Oxoammonium salt-promoted diverse functionalization of saturated cyclic amines with different dinucleophiles under mild conditions is presented. Specifically, when thiocyanate is used as a 1,3-dinucleophile, hexahydrothiazolo[4,5-b]pyridin-2(3H)-one derivatives are formed via the formation of the β-TEMPO-tethered cyclic iminium ion as a key intermediate. By contrast, when benzene-1,2-diamine is used as a 1,4-dinucleophile, 2-alkylquinoxaline derivatives are afforded via generation of the β-oxo cyclic iminium ion as a key intermediate. In addition, the usefulness of 2-alkylquinoxalines is showcased through their facile conversion into N-(2-oxo-2-(quinoxalin-2-yl)ethyl)nitrous amides featuring the synthetically useful N-NO moiety and the carbonyl group.

B(C6F5)3-Catalyzed α,β-Difunctionalization and C-N Bond Cleavage of Saturated Amines with Benzo[c]isoxazoles: Access to Quinoline Derivatives

Herein, we disclose a strategy to realize α,β-difunctionalization and C-N bond cleavage of saturated amines with benzo[c]isoxazoles via a B(C₆F₅)₃-catalyzed consecutive hydrogen-borrowing and [4 + 2] cycloaddition followed by a C-N bond cleavage process. In general, the reactions proceed efficiently in the absence of any oxidant and metal catalyst to afford a broad range of quinoline derivatives starting from easily accessible substrates in an atom-economical manner.

Oxoammonium Salt-Promoted Multifunctionalization of Saturated Cyclic Amines Based On β-Oxo Cyclic Iminium Ion Intermediates

Herein we describe a convenient method for multiple C(sp³)-H bond functionalization of saturated cyclic amines through oxoammonium salt-promoted oxidation to afford a β-oxo cyclic iminium ion as a key intermediate, followed by cascade addition with thiocyanate and diverse N-, O-, and S-containing nucleophiles in the green solvent and EtOH. Notably, chiral spiro azapolyheterocycles were prepared enantioselectively (>20:1 dr, up to 99% ee) when cysteine or serine esters were used as substrates. Moreover, the concise late-stage modification of several natural product derivatives was accomplished using this method.

Visible-Light-Induced Dual C(sp3)-H Bond Functionalization of Tertiary Amine via Hydrogen Transfer to Carbene and Subsequent Cycloaddition

Herein, we describe the dual C(sp³)-H bond functionalization of a tertiary amine through hydride-transfer-induced dehydrogenation, followed by cycloaddition, using an easily preparable diazoester as a new type hydride-acceptor precursor under mild, redox-neutral conditions. With carbene as a hydrogen acceptor, this method was demonstrated by the preparation of a broad range of functionalized isoxazoldines in moderate to good yields.

Cleavage and Reassembly of the C═O Bond of 2-Alkynylbenzaldehydes: A Metal-Free Access to Inden-1-ones

A metal-free approach to inden-1-ones from 2-alkynylbenzaldehydes mediated by pyrrolidine has been developed. The reaction proceeds under mild conditions in a step- and atom-economy process by cleaving the C═O bond and constructing new C-C as well as C═O bonds. Oxygen-18 and deuterium labeling experiments revealed an aza-Petasis-Ferrier rearrangement of an intermediate 1-amino-3-methylene-dihydroisobenzofuran.

Organocatalytic Asymmetric Multicomponent Cascade Reaction for the Synthesis of Contiguously Substituted Tetrahydronaphthols

Isobenzopyrylium ions are unique, highly reactive, aromatic intermediates which are largely unexplored in asymmetric catalysis despite their high potential synthetic utility. In this study, an organocatalytic asymmetric multicomponent cascade via dienamine catalysis, involving a cycloaddition, a nucleophilic addition, and a ring-opening reaction, is disclosed. The reaction furnishes chiral tetrahydronaphthols containing four contiguous stereocenters in good to high yield, high diastereoselectivity (up to >20:1), and excellent enantioselectivity (93-98% ee). The obtained products are important synthetic intermediates, and it is demonstrated that they can be used for the generation of frameworks such as octahydrobenzo[h]isoquinoline and [2.2.2]octane scaffolds. Furthermore, mechanistic experiments involving oxygen-18-labeling studies and density functional theory calculations provide a vivid picture of the reaction mechanism. Finally, the bioactivity of 16 representative tetrahydronaphthol compounds has been evaluated in U-2OS cancer cells with some compounds showing a unique profile and a clear morphological change.

Selective cleavage and reconstruction of C–N/C–C bonds in saturated cyclic amines: tunable synthesis of lactams and functionalized acyclic amines

Selective cleavage of C–N/C–C bonds in saturated cyclic amines for the tunable synthesis of lactams and functionalized acyclic amines under the promotion of oxoammonium salt and TBHP in the presence of different additives have been developed.

Recent advances in the functionalization of saturated cyclic amines

Functionalized cyclic amines are the essential structural moieties of numerous biologically active compounds. This review summarized the most recent advances in the C–H, C–N and C–C bond functionalization of saturated cyclic amines.