One-pot synthesis of pyrrolo[1,2-a]pyrazines via three component reaction of ethylenediamine, acetylenic esters and nitrostyrene derivatives

An effective route to pyrrolo[1,2-a]pyrazines is described via reaction of ethylenediamine,acetylenic esters and nitrostyrene derivatives in the presence of 20 mol%of sulfamic acid.     

Regioselective synthesis of 1,2,4,5-tetrasubstituted pyridines from Baylis-Hillman adducts via consecutive [3+2+1] annulation protocol

An efficient synthetic method of poly-substituted pyridines was developed. Various poly-substituted pyridines were prepared from the combination of Baylis-Hillman adducts (3 carbons), activated methylene compounds (2 carbons) and ammonium acetate (1 nitrogen) via [3+2+1] annulation protocol in good yields, regioselectively.     

BF3-promoted annulation of azonaphthalenes and ynamides for synthesis of benzo[e]indoles

A novel BF₃-promoted [3+2] annulation of azonaphthalenes and ynamides is described.This protocol provides a modular and efficient entry to functionalized amino benzo[e]indole derivatives smoothly.     

Synthesis and Neurotropic Activity of New Heterocyclic Systems: Pyridofuro[3,2-d]pyrrolo[1,2-a]pyrimidines,Pyridofuro[3,2-d]pyrido[1,2-a]pyrimidines and Pyridofuro[3′,2′:4,5]pyrimido[1,2-a]azepines

Background: Neurotic disturbances, anxiety, neurosis-like disorders, and stress situations are widespread. Benzodiazepine tranquillizers have been found to be among the most effective antianxiety drugs. The pharmacological action of benzodiazepines is due to their interaction with the supra-molecular membrane GABA-a-benzodiazepine receptor complex, linked to the Cl-ionophore. Benzodiazepines enhance GABA-ergic transmission and this has led to a study of the role of GABA in anxiety. The search for anxiolytics and anticonvulsive agents has involved glutamate-ergic, 5HT-ergic substances and neuropeptides. However, each of these well-known anxiolytics, anticonvulsants and cognition enhancers (nootropics) has repeatedly been reported to have many adverse side effects, therefore there is an urgent need to search for new drugs able to restore damaged cognitive functions without causing significant adverse reactions. Objective: Considering the relevance of epilepsy diffusion in the world, we have addressed our attention to the discovery of new drugs in this field Thus our aim is the synthesis and study of new compounds with antiepileptic (anticonvulsant) and not only, activity. Methods: For the synthesis of compounds classical organic methods were used and developed. For the evaluation of biological activity some anticonvulsant and psychotropic methods were used. Results: As a result of multistep reactions 26 new, five-membered heterocyclic systems were obtained. PASS prediction of anticonvulsant activity was performed for the whole set of the designed molecules and probability to be active Pa values were ranging from 0.275 to 0.43. The studied compounds exhibit protection against pentylenetetrazole (PTZ) seizures, anti-thiosemicarbazides effect as well as some psychotropic effect. The biological assays evidenced that some of the studied compounds showed a high anticonvulsant activity by antagonism with pentylenetetrazole. The toxicity of compounds is low and they do not induce muscle relaxation in the studied doses. According to the study of psychotropic activity it was found that the selected compounds have an activating behavior and anxiolytic effects on the models of “open field” and “elevated plus maze” (EPM). The data obtained indicate the anxiolytic (anti-anxiety) activity of the derivatives of pyrimidines, especially pronounced in compounds 6n, 6b, and 7c. The studied compounds increase the latent time of first immobilization on the model of “forced swimming” (FST) and exhibit some antidepressant effect similarly to diazepam. Docking studies revealed that compound 6k bound tightly in the active site of GABA_A receptor with a value of the scoring function that estimates free energy of binding (ΔG) at −7.95 kcal/mol, while compound 6n showed the best docking score and seems to be dual inhibitor of SERT transporter as well as 5-HT_1A receptor. Conclusions: Тhe selected compounds have an anticonvulsant, activating behavior and anxiolytic effects, at the same time exhibit some antidepressant effect.     

Efficient One-pot Synthesis of Pyrrolo[2,1-a]isoquinoline and Pyrrolo[1,2-a]quinoline Derivatives

A one-pot sequential reaction for efficient synthesis of pyrrolo[2,1-a]isoquinoline and pyrrolo[1,2-a]-quinoline derivatives has been developed. The reaction included firstly the Cu-catalyzed three-component reaction of isoquinoline(quinoline), acetylenedicarboxylate and alkynylbenzene and then Cs₂CO₃-promoted intramolecular cyclization reaction of initially formed 1-alkenyl-2-alkynyl-1,2-dihydroisoquinoline(1,2-dihydroquinoline).     

A highly diastereoselective [3+3] annulation reaction of aza-oxyallyl cations and nitrones

An efficient synthesis of 1,2,4-oxadiazinan-5-ones via [3+3] cycloaddition of in situ generated aza-oxyallyl cations with nitrones has been developed. The protocol features easy operation, excellent yields, excellent diastereo-control, broad substrate scope and good functional group tolerance.     

Screening of chiral phosphines as catalysts for the enantioselective [3+2] annulations of N-tosylimines with allenic esters

The use of chiral, binaphthyl-based phosphepines as catalysts improves previous results for the enantioselective [3+2] cyclisation reactions between allenic esters and N-tosylimines, both in terms of conversion rate and enantioselectivity. Pyrrolines bearing 1-naphthyl, phenyl, o-tolyl and p-MeO-phenyl substituents on the stereogenic alpha-carbon have been obtained with enantiomeric excesses up to 64-80%.     

Organocatalytic asymmetric [3 + 3] annulation of isatin N,N'-cyclic azomethine imines with enals: Efficient approach to functionalized spiro N-heterocyclic oxindoles

An unprecedented chiral secondary amine-catalyzed [3 + 3] annulation of isatin N,N'-cyclic azomethine imines with α,β-unsaturated aldehydes was developed. This strategy allowed the construction of structurally novel spiro N-heterocyclic oxindole derivatives in good yields (up to 91%) and good to excellent enantioselectivities (up to >99% ee), albeit with modest diastereoselectivities (up to 3.1:1 dr).     

Regioselective construction of polysubstituted phenols from Baylis-Hillman adducts via formal [4+2] annulation strategy

Polysubstituted phenol derivatives were synthesized regioselectively starting from the Baylis-Hillman adducts via the formal [4+2] annulation protocol as the key step.     

Synthesis of psudoheliotridane via formal [3+2] annulation and ring-closing metathesis

Base-induced coupling/cyclization stepwise [3+2] annulation of α-sulfonylacetamide with (Z)-2-bromoacrylates yielded polysubstituted pyroglutamates with three contiguous chiral centers with trans-trans orientation in a one-pot synthesis. The pyrrolizidine skeleton was obtained via the ring-closing metathesis (RCM) method. This facile strategy was used to synthesize psudoheliotridane.     

Asymmetric synthesis of tetrahydropyran[3,2-c]quinolinones via an organocatalyzed formal[3 + 3] annulation of quinolinones and MBH 2-naphthoates of nitroolefin

An efficient asymmetric and enantio-swithchable organocatalytic[3+3]annulation reaction using MBH-2-naphthoates of nitroalkenes and 4-hydroxyquinolin-2(1H)-ones has been developed.Densely substituted tetrahydropyrano[3,2-c]qui noli nones scaffolds with two adjacent stereogenic centers are obtained with high yield(up to 95%yield)and good stereoselectivities(up to>20:1 dr and 96%ee)in an enantio-switchable manner.Furthermore,gram scale synthesis was achieved and the nitro group could easily transform into an amino group without any appreciable loss in the diastereo-and enantioselectivity.     

Synthesis of spirooxindoles bearing 2,3-(or 2,5-)dihydrothiophene-2-thione moiety via [3+2] annulation of carbon disulfide with Morita-Baylis-Hillman carbonates of isatins

Various spirooxindoles bearing 2,3-(or 2,5-)dihydrothiophene-2-thione moiety have been synthesized via [3+2] annulation reaction of carbon disulfide and the nitrogen ylides derived from Morita-Baylis-Hillman carbonates of isatins. 2,3-Dihydro- and 2,5-dihydrothiophene-2-thione moieties were formed selectively depending on steric hindrance around the nitrogen ylides.     

Microwave-prompted rapid and efficient synthesis of 3-alkyl substituted imidazo[1,5-a]pyridines

Under regular heating and microwave irradiation, 3-alkyl substituted imidazo[1,5-a] pyridines were synthesized from 2,2＇- pyridil, di-2-pyridyl ketone and aliphatic aldehydes in the presence of ammonium acetate and acetic acid. Compared to the traditional heating condition, the reaction time under microwave irradiation was shorter and 3-alkyl imidazo[1,5-a]pyddines were given in higher yield.     

Phosphine-catalyzed [3+3] annulation reaction of modified tert-butyl allylic carbonates and substituted alkylidenemalononitriles

A phosphine-catalyzed [3+3] annulation reaction of modified tert-butyl allylic carbonates with various alkylidenemalononitriles to form cyclohexenes was developed. The use of protic solvent is crucial in this reaction. When non-polar solvent, toluene or xylene, was used, only non-cyclized product was obtained.     

Phosphine-catalyzed enantioselective [3+2] annulations of 2,3-butadienoates with imines

The first systematic screening of chiral phosphines in the cycloaddition reaction between 2,3-butadienoates and arylimines has led to the identification of fairly efficient catalysts. 2-Aryl-3-pyrrolines have been obtained with enantiomeric excesses up to 64%. In one instance, the enantiomeric excess could be increased to 91% ee by combining the enantioselective cyclization reaction with a crystallization step.     

Electrosynthesis of Dihydropyrano[4,3-b]indoles Based on a Double Oxidative [3+3] Cycloaddition

Oxidative [3+3] cycloadditions offer an efficient route for six-membered-ring formation. This approach has been realized based on an electrochemical oxidative coupling of indoles/enamines with active methylene compounds followed by tandem 6π-electrocyclization leading to the synthesis of dihydropyrano[4,3-b]indoles and 2,3-dihydrofurans. The radical–radical cross-coupling of the radical species generated by anodic oxidation combined with the cathodic generation of the base from O₂ allows for mild reaction conditions for the synthesis of structurally complex heterocycles.     

Crowned Macrocycles Containing Two Pyrrolo[1,2-a] Indoles Created By Intramolecular Fusion

Heterocyclic fused-ring systems are of utmost importance because of their presence in many natural products with biological activity. Pyrroloindoles are tricyclic heterocycles that are present in various bioactive and medicinally valuable compounds. Herein, we report the synthesis of phenylene-bridged bis-pyrrolo[1,2-a]indole crowned macrocycles 1 – 3 in which the pyrrolo[1,2-a]indole moieties were formed via intramolecular fusion. The macrocycles were thoroughly characterized by 1D and 2D NMR, HRMS and X-ray crystallographic studies. The X-ray structure revealed that the two pyrrolo[1,2-a]indole moieties were parallel to each other, and one pyrrolo[1,2-a]indole unit was deviated by an angle of 9.54° while the other pyrrolo[1,2-a]indole unit was deviated by an angle of 12.0° from the mean plane defined by 28 core atoms. The macrocycles 1 – 3 absorb in the visible region and readily undergo oxidations because of their electron rich nature. The macrocycles 1 – 3 upon treatment with trifluoroacetic acid (TFA) generates the corresponding cation radicals 1 – 3 ^.+ which were stable in the open air for a week. The cation radicals 1 – 3 ^.+ absorb strongly in the NIR region and the experimental observations on crowned macrocycles 1 – 3 were corroborated by DFT and TD-DFT studies.     

Diastereoselective Synthesis of 1,10-Dihydropyrrolo [ 1,2-a] [1,10]phenanthroline Derivatives via 1,3-Dipolar Cycloaddition Reaction

The functionalized 1,10-dihydropyrrolo[1,2-a][1,10]phenanthroline derivatives were synthesized in good yields and with high diastereoselectivity by 1,3-dipolar cycloaddition reactions of N-phenacylphenanthrolinium bromides or N-ethoxycarbonylmethylene phenanthrolinium bromide with various nitrostyrenes in acetonitrile at room temperature in the presence of triethvlamine,     

Electrosynthesis of Dihydropyrano[4,3‐b]indoles Based on a Double Oxidative [3+3] Cycloaddition

Oxidative [3+3] cycloadditions offer an efficient route for six‐membered‐ring formation. This approach has been realized based on an electrochemical oxidative coupling of indoles/enamines with active methylene compounds followed by tandem 6π‐electrocyclization leading to the synthesis of dihydropyrano[4,3‐b]indoles and 2,3‐dihydrofurans. The radical–radical cross‐coupling of the radical species generated by anodic oxidation combined with the cathodic generation of the base from O₂ allows for mild reaction conditions for the synthesis of structurally complex heterocycles.