2-Azabicyclo[2.2.2]octa-3,5-dione via a Nitrile Diels−Alder Reaction

Photo-induced radical transformations of tosyl cyanide

Tosyl cyanide is a commonly used reagent for cyanation and sulfonylation in organic synthesis and pharmaceutical chemistry. The photocatalytic transformations of tosyl cyanide are generally conducted under mild conditions. This minireview summarizes the recent progress of radical-involved transformations of tosyl cyanide via photo-induced cyanation or sulfonylcyanation.

Anion Cascade Reactions. Part I: Synthesis of 3-Isoquinuclidones from a Nazarov-like Reagent

A simple and atom-economical one-step protocol is described for the synthesis of biologically valuable 3-isoquinuclidones. The method proceeds from the simple starting materials, α-acyl N-arylcinnamamides, and can be performed under mild conditions in the presence of tBuOK. The key steps of this process are the double Michael addition reaction of a Nazarov-like reagent and the subsequent intramolecular hemiamination. These flexible intermolecular reactions could be performed on a gram scale.

Expanding the Chemical Space of Tetracyanobuta-1,3-diene (TCBD) through a Cyano-Diels-Alder Reaction: Synthesis, Structure, and Physicochemical Properties of an Anthryl-fused-TCBD Derivative

Tetracyanobuta-1,3-diene (TCBD) is a powerful and versatile electron-acceptor moiety widely used for the preparation of electroactive conjugates. While many reports addressing its electron-accepting capability have appeared in the literature, significantly scarcer are those dealing with its chemical modification, a relevant topic which allows to broaden the chemical space of this interesting functional unit. Here, we report on the first example of a high-yielding cyano-Diels-Alder (CDA) reaction between TCBD, that is, where a nitrile group acts as a dienophile, and an anthryl moiety, that is, acting as a diene. The resulting anthryl-fused-TCBD derivative, which structure was unambiguously identified by X-ray diffraction, shows high thermal stability, remarkable electron-accepting capability, and interesting electronic ground- and excited-state features, as characterized by a thorough theoretical, electrochemical, and photophysical investigation. Moreover, a detailed kinetic analysis of the intramolecular CDA reaction transforming the anthryl-TCBD-based reactant into the anthryl-fused-TCBD product was carried out at different temperatures.

Synthesis of Highly Substituted Pyridines via [4 + 2] Cycloadditions of Vinylallenes and Sulfonyl Cyanides

A convergent strategy for the synthesis of multisubstituted pyridines is described. Vinylallenes combine with commercially available arylsulfonyl cyanides in Diels-Alder cycloadditions to generate isopyridine cycloadducts that are converted to pyridines upon further heating or addition of a base. The 2-sulfonylpyridine products undergo nucleophilic aromatic substitution reactions with oxygen and carbon nucleophiles to provide access to a variety of highly substituted pyridines.

Construction of piperidine-2,4-dione-type azaheterocycles and their application in modern drug development and natural product synthesis

The review surveys the existing routes to piperidine-2,4-dione-type heterocycles including derivatives with the most vital types of biological activity. This heterocyclic platform is ideal for the construction of modern drugs and natural products.

Formal Bimolecular [2 + 2 + 2] Cycloaddition Strategy for the Synthesis of Pyridines: Intramolecular Propargylic Ene Reaction/Aza Diels-Alder Reaction Cascades

Two methods for the synthesis of multisubstituted pyridines are described. In each strategy, a highly reactive vinylallene is generated via an intramolecular propargylic ene reaction in the presence of an azadienophile. Reactions employing ethyl N-(tosyl)iminoacetate furnish an intermediate that undergoes elimination and isomerization upon the addition of DBU. The reaction of the intermediate vinylallene with TsCN leads to the isolation of a 2-sulfonylpyridine that serves as a versatile intermediate undergoing substitution reactions with oxygen and carbon nucleophiles.

Synthesis of 4-chalcogeno-1-aza-1,3-butadiene derivatives by intramolecular cyano-Diels-Alder reaction and borane-coordination-induced fluorescence enhancement

4-Thio-1-aza-1,3-butadiene derivatives 3 incorporating a rigid dibenzobarrelene skeleton were synthesized by the intramolecular cyano-Diels-Alder reaction of 9-anthryl cyanoethenyl sulfides 6. The thermal reaction of 6 afforded an equilibrium mixture of 3 and 6, but the cyclization was effectively promoted by the addition of BF3·Et2O or B(C6F5)3 to yield imine-borane adducts 8 and 9. The imine-borane adducts emit intense blue fluorescence both in solution and in the crystalline state. This is in stark contrast to free imines 3, which are weakly fluorescent. Selenium analogue 4 and N-oxide 12 of 3a were synthesized, along with their B(C6F5)3 adducts.

Cyano Diels-Alder and cyano ene reactions. Applications in a formal [2 + 2 + 2] cycloaddition strategy for the synthesis of pyridines

Two metal-free, formal [2 + 2 + 2] cycloaddition strategies for the construction of polycyclic pyridine derivatives are described that proceed via pericyclic cascade mechanisms featuring the participation of unactivated cyano groups as enophile and dienophile cycloaddition partners.

Hetero-Diels-Alder reaction of 1,3-bis(trimethylsilyloxy)-1,3-butadienes with arylsulfonylcyanides. Synthesis and antimicrobial activity of 4-hydroxy-2-(arylsulfonyl)pyridines

Hetero-Diels-Alder reactions of 1,3-bis(silyloxy)-1,3-butadienes with arylsulfonylcyanides afforded a variety of 4-hydroxy-2-(arylsulfonyl)pyridines. Several derivatives show antimicrobial activity against Gram-positive bacteria.

Synthesis of the parent and substituted tetracyclic ABCD ring cores of camptothecins via 1-(3-aryl-2-propynyl)- 1,6-dihydro-6-oxo-2-pyridinecarbonitriles

A new synthetic pathway to the parent and substituted ABCD ring cores of the camptothecin family of alkaloids was developed. The N-alkylation of 1,6-dihydro-6-oxo-2-pyridinecarbonitrile (2) with 3-bromo-1-phenylpropyne provided 3a using Curran's protocol. Treatment of 3a with a catalytic amount of DBU (5 mol %) at 110 degrees C for 12 h produced indolizino[1,2-b]quinolin-9(11H)-one (6a), the parent ABCD ring core of camptothecin, in essentially quantitative yield.

1H and 13C NMR spectral assignments of isoquinuclidine-3,5-dione derivatives

The 1H and 13C NMR spectra of six 5-substituted 2-azabicyclo[2.2.2]octane derivatives were fully assigned by COSY and HSQC experiments.