4-Halo-2-azabuta-1,3-dienes as intermediates in the rhodium carbenoid-initiated transformation of 2-halo-2H-azirines into 2,3-dihydroazetes and 2,5-dihydrooxazoles

Stable 2-Azaallyl Salts as a Bridge between 2H-Azirines and Densely Functionalized 2H-Pyrroles

An efficient protocol for the synthesis of stable 2-azaallyl anion salts by the reaction of alkyl 2-bromo-2H-azirine-2-carboxylates with trimethylsilyl cyanide/Bu4NF has been developed. The domino reaction proceeds in four steps via the cleavage of the azirine C-C bond to provide the tetrabutylammonium salts of stereochemically pure 2-azaallyl anions having U-configuration relative to the cyano groups. The anions with an ortho-substituted aryl group or styryl group exist as a mixture of two geometrical isomers across the N2-C3 bond. 2-Azaallyl anion salts have been shown to be convenient substrates for the one-pot synthesis of densely functionalized 2H-pyrroles by the alkylation-cyclization sequence.

Divergent Synthesis of Pyrazolo[1,5-a]pyridines and Imidazo[1,5-a]pyridines via Reagent-Controlled Cleavage of the C-N or C-C Azirine Bond in 2-Pyridylazirines

The three-membered ring in 2-(2-pyridyl)azirine-2-carboxylic esters and thioesters can undergo selective cleavage of either the N-C2 bond under copper(II) catalysis or the C-C bond under the action of HCl to provide isomeric azirine ring expansion products of pyrazolo[1,5-a]pyridine or imidazo[1,5-a]pyridine series, respectively. Mild catalytic reaction conditions for the formation of pyrazolopyridines make it possible to obtain them directly from 4-bromoisoxazoles by a one-pot, three-stage procedure without isolating the intermediate 2-bromoazirines and 2-(2-pyridyl)azirines.

Biological Activity of a 4-Hydroxy-Furanyl-Benzamide Derivative on Heart Failure

BACKGROUND

There are studies that suggest that some benzamide derivatives may exert effects on heart failure; however, their molecular mechanism is not very clear.

OBJECTIVE

The aim of this research was to evaluate the biological activity of a 4-hydroxy-furanyl-benzamide derivative against heart failure translated as area infarct.

METHODS

Biological activity produced by 4-hydroxy-furanyl-benzamide derivative against heart failure was determinate using an ischemia-reperfusion injury model. In addition, the effects exerted by the 4-hydroxy-furanyl-benzamide derivative on left ventricular pressure (LVP) was evaluated in the absence or presence of some drugs such as yohimbine, butaxamine, methoctramine and L-NAME using a model of rat heart isolated.

RESULTS

The results showed that 4-hydroxy-furanyl-benzamide derivative decrease both infarct area and LVP. However, the effect produced by 4-hydroxy-furanyl-benzamide derivative on LVP was inhibited in the presence of both methoctramine and L-NAME.

CONCLUSIONS

All these data suggest that biological activity produced by 4-hydroxy-furanyl-benzamide derivative on left ventricular pressure is through of both M₂-muscarinic receptor and nitric oxide synthase enzyme activation. It is important to mention that this phenomenon results as a decrease of both infarct area and heart failure.

One-Pot Synthesis of Multifunctionalized 1-Pyrrolines from 2-Alkyl-2H-azirines and Diazocarbonyl Compounds

A novel strategy for the synthesis of 1-pyrrolines based on formal [4 + 1] annulation of 2-alkyl-2H-azirines with diazocarbonyl compounds has been developed. This one-pot approach includes the Rh(II)-catalyzed formation of 4-alkyl-2-azabuta-1,3-dienes, followed by the DBU-promoted cyclization, and features a good substrate tolerance. The 1-pyrrolines containing an ester group at the C3 were prepared in a three-step one-pot procedure starting from 5-alkoxyisoxazoles. The cyclization of 2-azabutadienes to 1-pyrrolines most likely proceeds via the 6π electrocyclization of a conjugated NH-azomethine ylide.

1- and 2-Azetines via Visible Light-Mediated [2 + 2]-Cycloadditions of Alkynes and Oximes

Azetines, four-membered unsaturated nitrogen-containing heterocycles, hold great potential for drug design and development but remain underexplored due to challenges associated with their synthesis. We report an efficient, visible light-mediated approach toward 1- and 2-azetines relying on alkynes and the unique triplet state reactivity of oximes, specifically 2-isoxazolines. While 2-azetine products are accessible upon intermolecular [2 + 2]-cycloaddition via triplet energy transfer from a commercially available iridium photocatalyst, the selective formation of 1-azetines proceeds upon a second, consecutive, energy transfer process. Mechanistic studies are consistent with a stepwise reaction mechanism via N-O bond homolysis following the second energy transfer event to result in the formation of 1-azetine products. Characteristic for this method is its operational simplicity, mild conditions, and modular approach that allow for the synthesis of functionalized azetines and tetrahydrofurans (via in situ hydrolysis) from readily available precursors.

Electrocyclizations of Conjugated Azapolyenes Produced in Reactions of Azaheterocycles with Metal Carbenes

Conjugated azapolyenes (azabuta-1,3-dienes, aza-/diaza-/oxaza-/oxadiazahexa-1,3,5-trienes) are highly reactive in electrocyclization reactions, which makes them convenient precursors for the synthesis of a wide range of four-, five-, and six-membered nitrogen heterocycles that are of relevance for medicinal chemistry. Ring opening reactions of 2H-azirines and azoles containing an N–N or N–O bond, initiated by a transition metal carbene, have become increasingly important in recent years, since they easily allow the generation of azapolyenes with different numbers of double bonds and heteroatoms in various positions. This review summarizes the literature, published mainly in the last decade, on the synthetic and mechanistic aspects of electrocyclizations of azapolyenes generated by the carbene method.

Stereoselective assembly of 3,4-epoxypyrrolines via nucleophilic addition induced domino cyclization of 6-halo-1-oxa-4-azahexatrienes

A highly convergent assembly of 3,4-epoxypyrroline derivatives from azirines, diazo compounds and amines is developed based on the domino cyclization of 6-halo-1-oxa-4-azahexatrienes.

[2 + 1 + 1] Assembly of spiro β-lactams by Rh(ii)-catalyzed reaction of diazocarbonyl compounds with azirines/isoxazoles

A domino synthesis of dispiro-fused N-vinyl β-lactams from diazo-Meldrum's acid and 2H-azirines or 5-alkoxyisoxazoles via the "2-azabuta-1,3-diene formation/Staudinger ketene-imine cycloaddition" sequence is described. The Rh2(Piv)4-catalyzed formation of the 2-azabuta-1,3-diene intermediates in the first stage of the reaction sequence proceeds via addition of the rhodium carbenoid to the azirines/isoxazoles and provides the first example of the generation of iminium-type ylides from diazo-Meldrum's acid. This methodology was extended to monospiro-β-lactams, which were synthesized in two steps using acyclic α-diazocarbonyl compounds in the stage of the formation of 2-azabuta-1,3-dienes. The method allows for the rapid assemblage of the carbon part of the azetidin-2-one system from diazo compounds only and affords spiro- and dispiro-β-lactams in moderate yields. A bromine atom in the 2-bromoalkenyl moiety of the synthesized β-lactams can be easily substituted by hydrogen under catalytic hydrogenation conditions or by 2-pyridyl-substituent via the Stille cross-coupling reaction.

Expedient synthesis of 3-hydroxypyrrolesviaBu3SnH-triggered ionic 5-exo-trig-cyclization of 5-chloro-3-azamuconoate derivatives

An unprecedented application of tributyltin hydride as a reagent for reductive ionic 1,5-cyclization of 3-azamuconoates into variously substituted 3-hydroxy-1H-pyrroles is described.

Synthesis of 2-Aza-1,3-butadienes through Gold-Catalyzed Intermolecular Ynamide Amination/C-H Functionalization

A novel gold-catalyzed tandem intermolecular ynamide amination/C-H functionalization has been developed. A variety of highly functionalized 2-aza-1,3-butadienes can be obtained readily by utilizing this strategy. In addition, α-imino gold carbene intermediates are proposed in this amination reaction and with support by DFT (density functional theory) calculations.

Synthesis of New 2-Halo-2-(1H-tetrazol-5-yl)-2H-azirines via a Non-Classical Wittig Reaction

The synthesis and reactivity of tetrazol-5-yl-phosphorus ylides towards N-halosuccinimide/TMSN₃ reagent systems was explored, opening the way to new haloazidoalkenes bearing a tetrazol-5-yl substituent. These compounds were obtained as single isomers, except in one case. X-ray crystal structures were determined for three derivatives, establishing that the non-classical Wittig reaction leads to the selective synthesis of haloazidoalkenes with (Z)-configuration. The thermolysis of the haloazidoalkenes afforded new 2-halo-2-(tetrazol-5-yl)-2H-azirines in high yields. Thus, the reported synthetic methodologies gave access to important building blocks in organic synthesis, vinyl tetrazoles and 2-halo-2-(tetrazol-5-yl)-2H-azirine derivatives.