Ring Expansion of 1,2,3,4-Tetrahydroisoquinolines to Dibenzo[c,f]azonines. An Unexpected [1,4]-Sigmatropic Rearrangement of Nitrile-Stabilized Ammonium Ylides

Isoquinoline alkaloids from Corydalis edulis Maxim. Exhibiting insulinotropic action

Eleven undescribed isoquinoline analogues, namely edulisines A-K, along with sixteen known alkaloids, were isolated from the whole plants of Corydalis edulis. The structures of the isolated alkaloids were established on the basis of extensive spectroscopic data (1D and 2D NMR, UV, IR, and HRESIMS). Their absolute configurations were determined by single-crystal X-ray crystallographic analysis and ECD. Compounds (+)-1 and (-)-1 are a pair of undescribed isoquinoline alkaloids bearing a unique coupled pattern of coptisine and ferulic acid via Diels-Alder [4 + 2] cycloaddition, while compounds (+)-2 and (-)-2 feature benzo [1,2-d:3,4-d]bis [1,3]dioxole moiety. Compounds (+)-2, (-)-2, (-)-5, 10, 13, 15, 20, 22, and 23 significantly triggered the secretion of insulin in the HIT-T15 cells at a concentration of 40 μM.

Stereoselective synthesis of fused-, spiro- and bridged heterocycles via cyclization of isoquinolinium salts: A recent update

Isoquinoline and its derivatives are ubiquitous in natural alkaloids, synthetic materials and pharmaceuticals with broad spectrum of biological activities. In particular, isoquinolinium salts are important in organic synthesis because they...

Iron-catalyzed alkyne-carbonyl metathesis for the synthesis of 6,7-dihydro-5H-dibenzo[c,e]azonines

The synthesis of nine-membered rings via alkyne-carbonyl metathesis is reported. The alkyne and acetal units contained in a biaryl substrate undergo the intramolecular alkyne-carbonyl metathesis reaction under FeCl₃-catalysis to furnish the unexplored 6,7-dihydro-5H-dibenzo[c,e]azonines. The method provides an alternative to existing routes to nine-membered rings with cheap, non-toxic iron catalysts and milder conditions.

Gordonia hydrophobica Nitrile Hydratase for Amide Preparation from Nitriles

The active pharmaceutical ingredient levetiracetam has anticonvulsant properties and is used to treat epilepsies. Herein, we describe the enantioselective preparation of the levetiracetam precursor 2-(pyrrolidine-1-yl)butanamide by enzymatic dynamic kinetic resolution with a nitrile hydratase enzyme. A rare representative of the family of iron-dependent nitrile hydratases from Gordonia hydrophobica (GhNHase) was evaluated for its potential to form 2-(pyrrolidine-1-yl)butanamide in enantioenriched form from the three small, simple molecules, namely, propanal, pyrrolidine and cyanide. The yield and the enantiomeric excess (ee) of the product are determined most significantly by the substrate concentrations, the reaction pH and the biocatalyst amount. GhNHase is also active for the hydration of other nitriles, in particular for the formation of N-heterocyclic amides such as nicotinamide, and may therefore be a tool for the preparation of various APIs.

One-Pot Oxidative C-H Activation/Aza-Prins-Type Reaction of Tertiary Alkynylamines: A Counter Ion-Induced Iminium Ion-Alkyne Cyclization

Herein, the design and development of a new one-pot and metal-free oxidative C-H activation/aza-Prins type cyclization of alkynylamines is reported. The scope of this method was demonstrated by the preparation of ten new pyrido[2,1-a]isoquinolines in moderate to high yields (38-92%). Furthermore, a mechanistic proposal for the alkyne aza-Prins cyclization is described based on DFT calculations.

The aryne Sommelet–Hauser rearrangement

An aryne induced transition-metal-free and mild Sommelet–Hauser rearrangement of tertiary benzylamines for the synthesis of α-aryl amino acid derivatives in moderate to good yields and with broad substrate scope is presented.

Organic dye-catalyzed radical ring expansion reaction

Herein, we reported an attractive method for synthesizing medium-sized rings that are catalyzed by erythrosine B under fluorescent light irradiation. This synthetic approach featured mild conditions, a facile procedure, a broad substrate scope, and moderate-to-good yields.

Herein, we reported an attractive method for synthesizing medium-sized rings that are catalyzed by erythrosine B under fluorescent light irradiation.

Ammonium Ylide Mediated Cyclization Reactions

The use of readily accessible ammonium ylides for (asymmetric) transformations, especially cyclization reactions, has received considerable attention over the past two decades. A variety of highly enantioselective protocols to facilitate annulation reactions have recently been introduced as an alternative to other common methods including S-ylide-mediated strategies. It is the intention of this short review to provide an introduction to this field by highlighting the potential of ammonium ylides for (asymmetric) cyclization reactions as well as to present the limitations and challenges of these methods.

The reductive decyanation reaction: an overview and recent developments

This review presents an overview of the reductive decyanation reaction with a special interest for recent developments. This transformation allows synthetic chemists to take advantages of the nitrile functional group before its removal. Mechanistic details and applications to organic synthesis are provided.

A nitrile-stabilized ammonium ylide as a masked C–CN synthon in heterocyclization with amidine–imine: 3-component assembly to fused pyrimidine scaffolds

The title ylides possessing a unique reactivity-pattern and nitrile's dual role cyclo-condense with amidine–amine via a pathway of electronically-assisted nucleophilic substitutions and Hofmann elimination.

Synthesis and Photocatalytic Reactivity of Vinylsulfonium Ylides

Although sulfur ylides are textbook reagents in organic synthesis, surprisingly little variation of substituents on sulfur is usually observed. In particular, vinylsulfonium ylides have been neglected so far. Herein, we present a study on their synthesis and reactivity, including interesting behavior under photocatalytic conditions.

A short synthesis of pyridines from deprotonated α-aminonitriles by an alkylation/RCM sequence

α-Aminonitriles can serve as versatile key precursors for the synthesis of nitrogen containing heterocycles. After unsuccessful trials involving the [1,2]-Stevens rearrangement of nitrile-stabilized ammonium ylides, we herein report a simple three-step synthesis of substituted pyridines based on an alkylation/ring-closing metathesis/aromatization sequence.

A Highly Active System for the Metal-Free Aerobic Photocyanation of Tertiary Amines with Visible Light: Application to the Synthesis of Tetraponerines and Crispine A

A highly efficient metal-free catalytic system for the aerobic photocyanation of tertiary amines with visible light is reported. The use of air as terminal oxidant offers an improved safety profile compared with pure oxygen, the used compact fluorescent lamp (CFL) light sources are highly economical, and no halogenated solvents are required. This system not only proves to be effective for a wide variety of trialkylamines, pharmaceuticals, and alkaloids but remarkably also allows the lowest catalyst loading (0.00001 mol% or 0.1 ppm) ever reported for an organic dye. Bruylants reactions and C-alkylation/decyanations were performed on the obtained α-aminonitriles to demonstrate the postfunctionalization of complex molecules. The catalytic system is furthermore applied in the short and effective syntheses of the alkaloids (±)-crispine A and the tetraponerines T7 and T8.

[1,4]-sigmatropic rearrangement of chiral nitrones and their utilization in the synthesis of new iminosugars

A new mechanism of nitrone epimerization via [1,4]-sigmatropic rearrangement was proposed and a set of epimeric iminosugars was synthesized.

Transformation of Zwitterionic Pyridine Derivatives to a Spiro-Fused Ring System: Azoniabenzo[de]fluorine. Synthesis and Mechanistic Rationalization

Reaction of aryl- and benzylsulfanopyridinium amidates bearing a methyl group in position 6 with 2 equiv of diphenylketene afforded a spiro-fused ring system: azoniabenzo[de]fluorine. By use of an excess amount of ketene, a distinct reaction was observed via which a 1H-pyrrolo[3,2-b]pyridin-2(3H)-one derivative was furnished. The structure of the tetracyclic spiro-fused ring system was unambiguously confirmed by X-ray diffraction, and its formation was rationalized by DFT calculations.

Synthesis of imidazo[4,5-e]thiazolo[2,3-c]-1,2,4-triazine-2,8-diones via a rearrangement of imidazo[4,5-e]thiazolo[3,2-b]-1,2,4-triazine-2,7-diones in the reaction with isatins

An aldol condensation/skeletal rearrangement protocol for the synthesis of 7-ylideneimidazo[4,5-e]thiazolo[2,3-c]-1,2,4-triazines via the reaction of imidazo[4,5-e]thiazolo[3,2-b]-1,2,4-triazines and isatins has been developed.