Synthesis of Medium Ring Heterocycles Using an Intramolecular Heck Reaction

Palladium nanoparticle catalyzed synthesis of indoles via intramolecular Heck cyclisation

A system utilizing palladium(II)-PEG has been devised for the intramolecular Heck cyclization of N-vinyl and N-allyl-2-haloanilines. The synthesis of a variety of indoles, including 2,3-diester substituted ones and 3-methyl indoles, has been accomplished using this catalytic system. The N-vinyl starting materials are obtained by the aza-Michael addition of 2-haloanilines with alkynecarboxylate esters, which, upon cyclization, yield ester-substituted indoles. Conversely, N-allyl-2-haloanilines yield 3-methylated indoles as the major products. The high activity of the system is owed to the in situ generation of Pd nanoparticles.

A concise and stereoselective synthesis of the BCDF tetracyclic ring system of C19-diterpenoid alkaloids

A new synthetic route for the BCDF tetracyclic ring system of C19-diterpenoid alkaloids (C19-DTAs) has been developed. The key step is a Pd-catalyzed transannular alkenylation that installs a functionalized bridged F ring. The overall strategy is concise and stereoselective, and it provides a valuable new tool for the synthesis of C19-DTAs. The synthesis begins with a bridged [3.2.1] ring system, which is converted to a key intermediate through a series of highly regio- and stereoselective processes. The introduction of an allylic side chain with high precision is accomplished, culminating in a Pd-catalyzed transannular alkenylation that installs a functionalized bridged F ring to yield the BCDF tetracyclic analog of C19-DTAs.

Gram-Scale Total Synthesis of TAB with Cardioprotective Activity and the Structure-Activity Relationship of Its Analogs

Traditional Chinese medicine has been proven to be of great significance in cardioprotective effects. Clinopodium chinense (Lamiaceae) has unique advantages in the treatment and prevention of cardiovascular diseases. Tournefolic acid B (TAB) was proven to be a potent component against myocardial ischemia reperfusion injury (MIRI) from Clinopodium chinense (Lamiaceae). This article will attempt to establish a gram-scale synthesis method of TAB and discuss the structure-activity relationship of its analogs. The total synthesis of TAB was completed in 10 steps with an overall yield of 13%. In addition, analogs were synthesized, and their cardioprotective activity was evaluated on the hypoxia/reoxygenation of H9c2 cells. Amidation of the acid position is helpful to the activity, while methylation of phenolic hydroxyl groups greatly decreased the cardioprotective activity. The easily prepared azxepin analogs also showed cardioprotective activity. Most of the clogP values calculated by Molinspiration ranged from 2.5 to 5, which is in accordance with Lipinski's rule of 5. These findings represent a novel kind of cardioprotective agent that is worthy of further study.

Strategies in the synthesis of dibenzo[b,f]heteropines

The dibenzo[b,f]azepine skeleton is important in the pharmaceutical industry, not only in terms of existing commercial antidepressants, anxiolytics and anticonvulsants, but also in reengineering for other applications. More recently, the potential of the dibenzo[b,f]azepine moiety in organic light emitting diodes and dye-sensitized solar cell dyes has been recognised, while catalysts and molecular organic frameworks with dibenzo[b,f]azepine derived ligands have also been reported. This review provides a brief overview of the different synthetic strategies to dibenzo[b,f]azepines and other dibenzo[b,f]heteropines.

Evaluation of Biological Activity of a Diazocine Derivative against Heart Failure Using an Ischemia-Reperfusion Injury Model

BACKGROUND

There are studies, which suggest that some diazocine derivatives can exert effects on the cardiovascular system; however, these effects are not very clear.

OBJECTIVE

The aim of this research was to evaluate the biological activity of a diazocine derivative against heart failure translated as area infarct.

METHODS

Biological activity produced by diazocine derivatives against heart failure was determinate using an ischemia/reperfusion injury model. Besides, to characterize the molecular mechanism of effect exerted by diazocine derivative on left ventricular pressure (LVP) was determinate in an isolated rat heart model using nifedipine, PINAME TXA₂, and quinalizarin as controls.

RESULTS

The results showed that diazocine derivative decrease the infarct area and increase the LVP. However, the effect produced by diazocine derivative on LVP was inhibited in the presence of quinalizarin.

CONCLUSIONS

The results indicate that biological activity produced by diazocine derivative on left ventricular pressure is through protein CK2 activation; this phenomenon could be translated as a decrease in both infarct area and heart failure.

One-Pot Synthesis of Dibenzo[b,f]oxepines and Total Synthesis of Bauhinoxepin C

In this work, we report a novel and simple one-pot synthesis of substituted dibenzo[b,f]oxepines under transition-metal-free conditions. This cascade process involves nucleophilic aromatic substitution followed by Knoevanagel condensation, as evidenced by the isolated reaction intermediates. We have also achieved the synthesis of anticancer bauhinoxepin C in 7 steps with 5.1% overall yield using this synthetic approach.

Synthesis of Medium-Sized Heterocycles by Transition-Metal-Catalyzed Intramolecular Cyclization

Medium-sized heterocycles (with 8 to 11 atoms) constitute important structural components of several biologically active natural compounds and represent promising scaffolds in medicinal chemistry. However, they are under-represented in the screening of chemical libraries as a consequence of being difficult to access. In particular, methods involving intramolecular bond formation are challenging due to unfavorable enthalpic and entropic factors, such as transannular interactions and conformational constraints. The present review focuses on the synthesis of medium-sized heterocycles by transition-metal-catalyzed intramolecular cyclization, which despite its drawbacks remains a straightforward and attractive synthesis strategy. The obtained heterocycles differ in their nature, number of heteroatoms, and ring size. The methods are classified according to the metal used (palladium, copper, gold, silver), then subdivided according to the type of bond formed, namely carbon-carbon or carbon-heteroatom.

Intramolecular Palladium-Catalyzed Ring Opening of Oxabenzonorbornadienes with C1-Tethered Aryl Halides

The novel intramolecular ring opening of oxabenzonorbornadienes with C₁-tethered aryl halides was investigated using palladium catalysts to form fused tetracyclic frameworks. The reaction was generally found to synthesize 1,2-dihydronaphthalen-1-ol products with mild selectivity but was capable of synthesizing dehydrated naphthalene products in excellent yield and selectivity. Substituent effects on oxabenzonorbornadiene and on the iodoarene were explored along with the effects of varying tether length, where an efficient reaction was observed in nearly all cases. A total of 16 examples are reported with yields ranging from 0 to 96%.

Efficient construction of pyrrolo[1′,2′:1,2]azocino[4,5-c]quinolines via cascade cycloaddition and annulation reaction

Novel polysubstituted pyrrolo[1′,2′:1,2]azocino[4,5-c]quinolines were efficiently synthesized by a three-component reaction in refluxing methanol and a sequential domino annulation in refluxing acetonitrile.

Synthesis of medium-sized (6-7-6) ring compounds by iron-catalyzed C-H activation/annulation [corrected]

In this report, we have described a FeCl3-catalyzed process involving intramolecular annulation of o-phenoxy diarylacetylenes via hydroarylation to afford a series of biologically potent fused seven-membered (6-7-6) ring compounds under mild reaction conditions. This reaction was believed to proceed through Friedel-Crafts type sequential carbometallation followed by protonation to produce phenyldibenz[b,f]oxepines. This method was also extended to synthesize seven-membered rings that are fused with coumarins.

Regioselective access of alkylidendibenzo[c,f]oxocine framework via cyclocarbopalladation/cross-coupling cascade reactions and reductive Heck strategy

Palladium-catalyzed dual strategies of cascade cyclocarbopalladation/cross-coupling of alkynes and a reductive Heck reaction have been developed to construct dibenzo[c,f]oxocine frameworks with tri- and tetra-substituted exo-cyclic alkenes with high stereo- and regio-control.

BF3·OEt2-mediated one pot synthesis of 10-indolyldibenzo[b,f]azepine derivatives via tandem ring expansion and C–C bond formation

A simple and efficient one pot protocol was developed for the synthesis of new structurally diverse 10-indolyldibenzo[b,f]azepine derivatives.

A new recyclable 1,4-bis(3-methylimidazolium-1-yl)butane ditribromide [bMImB]·(Br3)2 ionic liquid reagent for selective bromination of anilines or phenols and α-bromination of alkanones under mild conditions

1,4-Bis(3-methylimidazolium-1-yl)butane ditribromide [bMImB]·(Br₃)₂ has been synthesized and explored as a new efficient brominating agent.

Monobromomalononitrile: an efficient regioselective mono brominating agent towards active methylene compounds and enamines under mild conditions

The potential of monobromomalononitrile (MBM) as a convenient source of cationic bromine in organic bromination reaction has been explored.

New short strategy for the synthesis of the dibenz[b,f]oxepin scaffold

In this report a short and efficient synthesis of the dibenz[b,f]oxepin framework through intramolecular SNAr and McMurry reactions is described. The diaryl ethers required for the McMurry reaction have been obtained in good yields under microwave-assisted conditions of the reaction of salicylaldehydes with fluorobenzaldehydes without catalysts. Application of an intramolecular McMurry reaction to the synthesized diarylethers using TiCl4/Zn in THF gave the target dibenzo[b,f]oxepin system in 53%-55% yields.

An efficient access to the synthesis of novel 12-phenylbenzo[6,7]oxepino[3,4-b]quinolin-13(6H)-one derivatives

An efficient access to the tetracyclic-fused quinoline systems, 12-phenylbenzo[6,7]oxepino[3,4-b]quinolin-13(6H)-one derivatives 4a–l, is described, involving the intramolecular Friedel–Crafts acylation reaction of 2-(phenoxymethyl)-4-phenylquinoline-3-carboxylic acid derivatives 3a–l aided by the treatment with PPA (polyphosphoric acid) or Eaton’s reagent. The required starting compound (2) was obtained by Friedländer reaction of 2-aminobenzophenone (1) with 4-chloroethylacetoacetate by using CAN (cerium ammonium nitrate, 10 mol %) as catalyst at room temperature. The substrates 3a–l were prepared through one-pot reaction of ethyl 2-(chloromethyl)-4-phenylquinoline-3-carboxylate (2) and substituted phenols. Our developed strategy, involving a three-step route, offers easy access to tetracyclic-fused quinoline systems in short reaction times, and the products are obtained in moderate to good yields.

Microwave-assisted synthesis of medium-sized heterocycles

The development of new strategies for synthesis of medium-sized heterocycles has remained a highly attractive but challenging proposition. In the last few years, the application of microwave irradiation has greatly facilitated the construction of such heterocyclic ring systems through a myriad of different synthetic approaches. This feature article illustrates the progress made in the microwave-assisted synthesis of medium-sized heterocycles with an emphasis on examples describing the use of a dedicated microwave synthesizer.