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Modification of the quinolizine backbone of the alkaloid lupinine was carried out by introducing substituted 1,2,3-triazole. When NaN3 acts upon the product of the reaction of lupinine with methanesulfonyl chloride, lupinyl azide is formed which in the reaction with terminal alkynes in the presence of aqueous CuSO4 and sodium ascorbate forms the corresponding (1S,9aR)-1-[(1,2,3-triazol-1-yl)-methyl]octahydro-1H-quinolizines with various substituents at the C-4 position of the triazole ring. The structures of lupinine methanesulfonate and 1-[(1,2,3-triazol-1-yl)methyl]octahydroquinolizines were confirmed by X-ray structural analysis. 1-[(1,2,3-Triazol-1-yl)methyl]octahydroquinolizines containing a hydroxymethyl or 2-hydroxypropan-2-yl substituent at the C-4 position of the triazole ring exhibit pronounced analgesic activity.

A novel protocol for the synthesis of quinolizines (3) and quinolizinium salts (4) from chromone-3-carboxaldehydes 1 with ethyl 2-(pyridine-2-yl)acetate derivatives 2via an unprecedented cascade reaction in water was constructed. As a result, functionalized quinolizines (3) bearing a chromone skeleton were prepared by simple reflux of the mixture of chromone-3-carboxaldehydes with ethyl 2-(pyridine-2-yl)acetate derivatives in water. Quinolizinium salts (4) were also prepared in water under acidic conditions. The formation of quinolizinium salts was accompanied by the formation of two bonds and the cleavage of one bond in a single step. This protocol can be used in the synthesis of a wide variety of quinolizines and quinolizinium salts, and is suitable for combinatorial and parallel syntheses of quinolizine derivatives natural-like products. This approach has several advantages such as the use of an environmentally friendly solvent, simple and practical operation (with filtration and washing without column chromatography separation), excellent yields (83–96%), and formation of a product with potential biological activity.

2-Pyridone is characterized by a very wide range of reactivity of a different nature, ranging from electrophilic aromatic substitution, CH–metal-mediated reactions, and NH/OH functionalization of both possible lactam/lactim tautomers, through cycloaddition, to nucleophilic addition and transformation of the tautomeric C=O/C–OH moiety. The high availability of 2-pyridones and the possibility of their far-reaching functionalization additionally increased their values. Therefore, they are very useful building blocks for the synthesis of structurally diverse piperidine and pyridine compounds, including naturally occurring 2-pyridones. This review reports on the use of simple 2-pyridones in the synthesis of alkaloids and alkaloids-inspired compounds based on the piperidine or pyridine framework.1 Introduction2 Structure, Availability, and Reactivity of 2-Pyridones3 Monocyclic Piperidine Alkaloids from 2-Pyridones4 Polycyclic Alkaloids, Their Derivatives, and Alkaloid-Inspired Compounds from 2-Pyridones4.1 New Ring Formation Involving C/N Atoms of the 2-Pyridone Ring4.1.1 Indolizine-Fused 2-Pyridones: Camptothecins and Related Compounds4.1.2 Other Indolizines from 2-Pyridones4.1.3 Compounds Bearing the Quinolizine Ring System4.2 New Ring Formation Involving C/C Atoms of the 2-Pyridone Ring4.2.1 C-2/C-3 Ring Fusion4.2.2 C-3/C-4 Ring Fusion4.2.3 C-4/C-5 Ring Fusion4.2.4 C-5/C-6 Ring Fusion4.2.5 C-2/C-4 Ring Bridge4.2.6 C-2/C-6 Ring Bridge4.2.7 C-3/C-5 Ring Bridge4.2.8 C-3/C-6 Ring Bridge4.2.9 C-4/C-6 Ring Bridge5 Conclusion

Two crystals of quinolizidine compounds; systematic name: (rac)-(7,8,9,9a)-tetrahydro-4H-thieno[2,3-b]quinolizine-6,10-dione, (I), and (rac)-(9a,10)-10-hydroxy-8,9,9a,10-tetrahydro-4H-thieno[2,3-b]quinolizin-6(7H)-one, (II), have been compared and characterized by single-crystal X-ray diffraction and electronic analysis. N-heterocyclic rings in both structures are not planar and adopt a half-chair conformation. The molecules of (I) are linked via weak C–H···O hydrogen bonds into chains along c axis. While the crystal stacks in compound (II) are formed by strong O–H···O hydrogen bonds the molecules link into infinite zig-zag chains along the b axis. In both crystal structures, π–π stacking and C–H···π interactions are also observed. Calculation of the net atomic charges shows that O atoms in both compounds carry a relatively large negative charges, in comparison with the corresponding H atoms. Crystal, molecular and electronic structures of these compounds, which are influenced by hydrogen-bonded assemblies in the molecular crystals, are discussed in detail. Crystal, molecular and electronic structures of two related tricyclic compounds containing thienoquinolizidine ring skeleton, both structures have similar quinolizine ring moieties assuming conformations resembling half-chair.

Iridium(I) N-heterocyclic carbene complexes of formula Ir(κ2O,O’-BHetA)(IPr)(η2-coe) [BHetA=bis-heteroatomic acidato, acetylacetonate or acetate; IPr=1,3-bis(2,6-diisopropylphenyl)imidazolin-2-carbene; coe=cyclooctene] have been prepared by treating Ir(κ2O,O’-BHetA)(η2-coe)2 complexes with IPr. These complexes react with 2-vinylpyridine to afford the hydrido-iridium(III)-alkenyl cyclometalated derivatives IrH(κ2O,O’-BHetA)(κ2N,C-C7H6N)(IPr) through the iridium(I) intermediate Ir(κ2O,O’-BHetA)(IPr)(η2-C7H7N). The cyclometalated IrH(κ2O,O’-acac)(κ2N,C–C7H6N)(IPr) complex efficiently catalyzes the hydroalkenylation of aromatic and aliphatic terminal alkynes and enynes with 2-vinylpyridine to afford 2-(4R-butadienyl)pyridines with Z,E configuration as the major reaction products (yield up to 89 %). In addition, unprecedented (Z)-2-butadienyl-5R-pyridine derivatives have been obtained as minor reaction products (yield up to 21 %) from the elusive 1Z,3gem-butadienyl hydroalkenylation products. These compounds undergo a thermal 6π-electrocyclization to afford bicyclic 4H-quinolizine derivatives that, under catalytic reaction conditions, tautomerize to 6H-quinolizine to afford the (Z)-2-(butadienyl)-5R-pyridine by a retro-electrocyclization reaction., Financial support from the Spanish Ministerio de Ciencia e Innovación (MICINN/FEDER) under Project PID2019-103965GB-I00, and the Departamento de Ciencia, Universidad y Sociedad del Conocimiento del Gobierno de Aragón (group E42_20R) is gratefully acknowledged. I.G. thanks the Humboldt Foundation for a research fellowship.

Here we report the 1,3-dipolar cycloaddition of polycyclic aromatic azomethine ylides with nitriles to produce highly fused imidazole derivatives, that is, tribenzo[b,g,ij]imidazo[2,1,5-de]quinolizine. The advantages of this transformation are the broad substrate scope and the good functional group compatibility. The subsequent palladium-catalyzed intramolecular cyclization provides an efficient approach to further π-extended imidazoles, that is, 14b1,15-diazadibenzo[fg,ij]cyclopenta[rst]pentaphene.

As a signal molecule, SO2 participates in many complex physiological processes. Therefore, in view of the addition properties of SO2 derivatives to unsaturated olefins, we reasonably designed a set of ratiometric fluorescent probes (NB1, NB2, NB3), and evaluated the influence of the coumarin moiety on the optical properties of the probes. Amongst the probes when the 7-position is substituted by a fused quinolizine (julolidine) unit, the probe NB2 shows a change from red to green fluorescence upon reaction with SO2, and has excellent optical properties: 136 nm emission band gap, 230 s response time, high selectivity, and excellent sensitivity. More valuable is the fact that NB2 can be used in cell imaging experiments, real sample detection, and employed to prepare fluorescent test paper for the qualitative test of SO2 gas, indicating that NB2 can be used as a powerful tool for the detection of SO2 derivatives.

Indolo[2,3-a]quinolizidine 1 (Scheme 1) has an interesting history. First synthesized by Keufer1 in 1950, this tetracyclic amine was subsequently prepared by several others,2–7 only later to be dis...

An efficient synthesis of 6-oxo-1,2,3,4,5,7,12,12b-octahydroindolo[2,3-α]quinolizine from 2-acetylpyridine and phenylhydrazine is described. This derivative of the natural alkaloid desbromoarborescidine A is an important entry point to the sarpagine-vobasine family of plant alkaloids.

Reversible chemically stimulated cyclization/cycloreversion reactions are of great interest and highly demanding for developing molecular switches, such as fluorescent probes. Herein, ultrafast and reversible cyclization/cycloreversion reactions of 4-imino-4H-quinolizine-1-carbonitrile (IMQU) derivatives, induced by H+/OH−, were developed as a new strategy for pH sensing. 1H NMR, HRMS techniques and quantum chemical methods applied to the pH sensing behavior of IMQUs reveal its legitimate mechanism. The IMQU derivatives targeted lysosomes and displayed bright emission, large Stokes shifts, robust fatigue resistance, and superior photostability over commercially available Lyso-Tracker Red. A good correlation was found between pKa values and natural atomic charges at the C-1 atom of the aromatic substituents, which should enable rational tuning of the pKa values.

An activatable BODIPY probe for in vitro detection and fluorescence cell imaging of free Mg2+ without interference from Ca2+ is described. Fluorescence amplification of the probe is observed upon detection of physiological concentrations of Mg2+ due to reduced rotation of the fluorophore and effective chelation by a quinolizine-based core.

The reaction of 2-oxo-2 H-chromene-3-carbonitriles with dialkyl acetylenedicarboxylates and pyridines results in a three-component condensation reaction in which the 2-oxo-2 H-chromene-3-carbonitrile group acts as a dipolarophile to produce benzopyrano[3,4- a] quinolizines under mild conditions in good yield.

A method for preparation of thermodynamic (4R,11bS)-benzo[a]quinolizine-2-one derivatives in good enantio- and diastereoselectivity by a one-pot oxidative formal aza-Diels−Alder reaction of 1,2,3,4-tetrahydroisoquinolines and α,β-unsaturated ketones is described. The reaction proceeds via tandem Ru-catalyzed amine dehydrogenation using TBHP as the oxidant and a chiral thiourea-catalyzed formal aza-[4+2] cycloaddition, providing a step-economical strategy for synthesis of valuable heterocyclic products.

A common strategy was developed to access both indolizino[8,7-b]indole and indolo[2,3-a]quinolizine derivatives from tryptamine-N-ethynylpropiolamide substrates in a switchable fashion via tuning both the electronic effects and steric effects.

Matrine derivative MASM (M19) is a quinolizine alkaloid with diverse pharmacological effects including preventing postmenopausal osteoporosis. In the current study, we observed that pretreatment with M19 inhibited cell apoptosis of murine osteoblastic MC3T3-E1 and primary osteoblasts induced by 1 μM dexamethasone in a dose-dependent manner. Our study also showed that pretreatment with M19 significantly prevented the upregulation of p53 that is caused by dexamethasone but had no effect on the p53 mRNA expression levels. Further immunoprecipitation (IP) experiments showed that M19 treatment increases the ubiquitination of p53 in dexamethasone-treated MC3T3-E1 cells. The expression of USP14, a deubiquitinating enzyme, increased with dexamethasone and decreased with M19 pretreatment. Co-IP experiments demonstrated the interaction between USP14 and p53, and the induced effect of a USP14 inhibitor (IU1) on p53 ubiquitination, which indicated that USP14 is a potential deubiquitinase for p53. Furthermore, pretreatment with IU1 or a p53 inhibitor (PFT-α) partially blocked dexamethasone-induced apoptosis of MC3T3-E1 cells. The overexpression of USP14 or p53 reversed the antiapoptotic effect of M19 in dexamethasone-treated MC3T3-E1 cells. In addition, PFT-α treatment remarkably blocked the effects of USP14 overexpression. In summary, our findings suggest that M19 exerts protective effects on dexamethasone-treated MC3T3-E1 cells by regulating USP14/p53.

Phosphodiesterase 5A enzyme has been the upcoming and promising target in hypertension management. In this research, reported 270 bioactive natural products having antihypertensive potential were selected and docked against PDE5A using vLife MDS 4.6 software. Based on docking score, π-stacking, H-bond and ionic interactions with PDE5A, 82 tricyclic compounds were selected for further study. Protein residue Gln817A was associated in H-boding, Leu804A in ionic interaction whereas Val782A and Phe820A were associated in π-stacking interaction with ligand. In silico docking studies resulted in discovery of oxygen containing naphthofuran and nitrogen and oxygen containing pyrano quinolizine tricyclic lead scaffolds as novel PDE5A inhibitors. Additionally, developed pharmacophore model suggested that one centre of hydrogen bond acceptor, one aromatic centre and two aliphatic centres are minimum pharmacophoric features required in the molecule so as to show sildenafil like activity. The identified lead scaffolds would provide novel platform for drug discovery of bioactive natural products.

A Cu(OAc)2-catalyzed domino tricyclization between naphthalene-1,8-diamine and 2-(phenylethynyl)benzaldehyde is described, enabling aerobic oxidative dehydrogenation coupling to access heptacyclic quinolizino[3,4,5,6-kla]perimidines. In this reaction, the formation of three new rings and four new bonds was achieved in a functional-group-compatible fashion, allowing a facile method toward fused aza-heterocycles containing both quinolizine and perimidine moieties.

A 4′-hydroxyflavylium bearing a julolidine (2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizine) substituent in position 7 to minimize the amine rotation was characterized. Similarly to the 7-(N,N-diethylamino)-4′-hydroxyflavylium, the compound does not show trans-cis chalcone photoisomerization in water and the fluorescence emission quantum yield of its flavylium cation (Φf = 0.004) is 2.5 times lower than the non-rigid analog. These results seem to exclude a Twisted Intramolecular Charge Transfer (TICT) model to explain the lack of photoisomerization of the chalcones and the small quantum yield of fluorescence emission in these compounds. The julolidine substituent is however slightly more efficient to prevent the hydration of the flavylium cation than the non-rigid amines. In both compounds hydration takes place only at basic pH values through the attack of the hydroxyl in position 2 of the quinoidal base. The chalcone forms of the julolidine derivative are unstable and decompose after several hours. The rate of flavylium formation from trans-chalcone is slow but increases directly with the mole fraction of protonated trans-chalcone for 1

A facile multi-component process for the synthesis of perfluoroalkylated quinolizine derivatives was achieved using various arylidenemalononitriles, pyridine, and methyl perfluoroalk-2-ynoates as starting materials. Moderate yields were obtained under mild condition. The structures of perfluoroalkylated quinolizine derivatives were characterized by means of 1H NMR, 13C NMR, 19F NMR, IR, LRMS and HRMS. Furthermore, the reaction mechanism was proposed.

Ent-homocyclopiamine B (1), a new prenylated indole alkaloid bearing an alicyclic nitro group along with 2-methylbutane-1,2,4-triol (2) were isolated from an endophytic fungus Penicillium concentricum of the liverwort Trichocolea tomentella (Trichocoleaceae). The structure of 1 was elucidated through extensive spectroscopic analyses and comparison with data reported for a structurally related nitro-bearing Penicillium metabolite, clopiamine C (3), which contain an indolizidine ring instead of the quinolizine ring in 1. The new compound, ent-homocyclopiamine B, exhibited slight growth inhibition against Gram-positive bacteria. Based on the reported biosynthesis of related compounds and the isolation of the mevalonic acid derived compound 2-methyl-1,2,4-butanetriol (2), we proposed that ent-homocylopiamine B (1) was biosynthesized from lysine and prenyl group-producing mevalonic pathway.

Octahydroindolo[2,3-a]quinolizine ring system forms the basic framework comprised of more than 2000 distinct family members of natural products. Despite the potential applications of this privileged substructure in drug discovery, efficient, atom-economic and modular strategies for its assembly, is underdeveloped. Here we show a one-step build/couple/pair strategy that uniquely allows access to diverse octahydroindolo[2,3-a]quinolizine scaffolds with more than three contiguous chiral centers and broad distribution of molecular shapes via desymmetrization of the oxidative-dearomatization products of phenols. The cascade demonstrates excellent diastereoselectivity, and the enantioselectivity exceeded 99% when amino acids are used as chiral reagents. Furthermore, two diastereoselective reactions for the synthesis of oxocanes and piperazinones, is reported. Phenotypic screening of the octahydroindolo[2,3-a]quinolizine library identifies small molecule probes that selectively suppress mitochondrial membrane potential, ATP contents and elevate the ROS contents in hepatoma cells (Hepa1–6) without altering the immunological activation or reprogramming of T- and B-cells, a promising approach to cancer therapy., Methods enabling the synthesis of diverse collections of nature-inspired compounds with potential medicinal use are sought after in drug design. Here, the authors report a build/couple/pair strategy to efficiently construct chiral polycyclic scaffolds and show their diversification for drug discovery screening.

The cascade oxidative annulation reactions of aryl imidazoles with two molecules of alkynes via multiple C-H activation proceed efficiently in the presence of [Cp*RhCl2]2 and Cu(OAc)2·H2O to give substituted benzo[ij]imidazo[2,1,5-de]quinolizine-based polyheteroaromatic compounds. This method is compatible with various functional groups, which are very useful for further synthetic transformations.

A facile synthetic method for the construction of 2-substituted-4-oxo-4H-quinolizine-based core structure has been successfully developed. The synthesis made use of a one-pot Stobbe condensation followed by cyclization starting from the commercially available 2-pyridinecarbaldehyde. The structure of the formed 4-oxo-4H-quinolizine-2-carboxylate was fully confirmed by mass spectra, 1H NMR and 13C NMR, correlation spectrography, heteronuclear multiple bond correlation, and heteronuclear single quantum coherence (HSQC) spectra. The ethyl carboxylate moiety was then further functionalized via direct aminolysis by a range of amines to afford the corresponding 4-oxo-4H-quinolizine-2-carboxamides 4a–i in moderate to good yields.

Pyridines were found to be a convenient nucleophile in the copper(I)-catalyzed synthesis of N-tosyl-4-iminoquinolizines from 2-pyridyl compounds. Intramolecular cyclization of an in situ generated ketenimine and a tethered pyridine, followed by a base-promoted oxidation, affords the desired products in moderate to good yields under mild reaction conditions.

Tetrahydroberberine (systematic name: 9,10-dimethoxy-5,8,13,13a-tetrahydro-6H-benzo[g][1,3]benzodioxolo[5,6-a]quinolizine), C20H21NO4, a widely distributed naturally occurring alkaloid, has been crystallized as a racemic mixture about an inversion center. A bent conformation of the molecule is observed, with an angle of 24.72 (5)° between the arene rings at the two ends of the reduced quinolizinium core. The intermolecular hydrogen bonds that play an apparent role in crystal packing are 1,3-benzodioxole –CH2...OCH3and –OCH3...OCH3interactions between neighboring molecules.

The stereoselective synthesis of (−)-protoemetinol has been accomplished through nine steps from a known homoallylic amine. The key steps of the synthesis involve the efficient preparation of an aza-Claisen rearrangement (ACR) precursor using cross metathesis and amide enolate-induced ACR followed by acid-catalyzed transannulation for the elaboration of the benzo[α]quinolizine skeleton and three stereogenic centers. This unique synthetic route envisages a unified and versatile strategy for the synthesis of 2,3-disubstituted benzo[α]quinolizidine.

Highly active antiretroviral therapy (HAART) has been widely adopted to control the HIV-1 infection successfully. HIV-1 integrase (IN) inhibitors are primary drugs in HAART regimens targeting integration step in the HIV-1 life cycle. However, due to the emergence of viral resistance and cross-resistance amongst drugs, there is a pressing need for new and potent IN inhibitors. This review covers the three patents describing spirocyclic and phosphate substituted quinolizine derivatives as novel HIV-1 IN inhibitors for the discovery of new anti-HIV-1 drug candidates. Areas covered: This review is focused on spirocyclic and phosphate substituted quinolizine derivatives bearing the same metal chelation scaffold as novel HIV-1 IN inhibitors. Expert opinion: Generally, privileged structure-based optimizations have emerged as an effective approach to discover newly antiviral agents. More generally, due to the similar Mg2+ catalytic active centers of endoribonucleases, some divalent metal ion chelators were found to be versatile binders targeting multiple metalloenzymes. Therefore, privileged structure-based scaffold re-evolution is an important tactic to identify new chemotypes, to explore unknown biological activities, or to provide effective ligands for multiple targets by modifying the existing active compounds.

Dihydroberberine (systematic name: 9,10-dimethoxy-6,8-dihydro-5H-1,3-dioxolo[4,5-g]isoquinolino[3,2-a]isoquinoline), C20H19NO4, a reduced form of pharmacologically important berberine, crystallizes from ethanol without interstitial solvent. The molecule shows a dihedral angle of 27.94 (5)° between the two arene rings at the ends of the molecule, owing to the partial saturation of the inner quinolizine ring system. Although lacking classical O—H or N—H donors, the packing in the crystalline state is clearly governed by C—H...N and C—H...O hydrogen bonds involving the two acetal-type C—H bonds of the 1,3-dioxole ring. Each dihydroberberine molecule is engaged in four hydrogen bonds with neighbouring molecules, twice as donor and twice as acceptor, thus forming a two-dimensional sheet network that lies parallel to the (100) plane.

Novel, one-pot, three-component reactions of the zwitterions generated in situ from pyridine and acetylenic esters with alkoxymethylenemalononitriles via 1,4-dipolar cycloadditions are described. The reactions afforded dialkyl 1,1-dicyano-2-alkoxy-1,9a-dihydro-2H-quinolizine-3,4-dicarboxylate derivatives in good to high yields without using any catalyst or activation. Structural, electronic, energetic, and mechanistic details of the reaction are also revealed by density functional theory (DFT) calculations, which strongly support the exclusive formation of the observed products.

The three-component reactions of 4-dimethylamino- or 4-methoxypyridine with acetylenedicarboxylates and arylidene cyanoacetates showed very interesting molecular diversity. The polysubstituted 1,8,9,9a-tetrahydro-4H-1,4-ethanoquinolizines, 2H-pyran-2,3-dicarboxylates, and buta-1,3-diene-1,2,4-tricarboxylates derivatives can be formed in high yields and with good diastereoselectivity depending on the substrates and reaction conditions.

International audience; Benzo[a]quinolizine is an important heterocyclic framework that can be found in numerous bioactive compounds. The general scheme for the synthesis of these compounds was based on the preparation of the appropriate dihydroisoquinolines by Bischler-Napieralski cyclization with good yields, followed by the Pemberton method to form the oxazinones or pyridones derivatives via acyl-ketene imine cyclocondensation. All the synthesized compounds were assayed in vitro for their ability to inhibit mitochondrial respiratory chain. Most of the tested compounds were able to inhibit the integrated electron transfer chain, measured as NADH oxidation, which includes complexes I, III and IV, in the low micromolar range. Oxazino[2,3-a]isoquinolin-4-ones displayed greater activity than their pyrido[2,1-a]isoquinolin-4-ones analogs. Indeed, the presence of a furan ring in C₂ position of oxazino[2,3-a]isoquinolin-4-ones provided the compound (1g) with the most potent biological activity. Therefore, these compounds and especially the oxazinone derivatives are in the tendency of the new less toxic antitumor agents that target mitochondrial electron transport chain in a middle range potency.

Three-component condensation of lower aliphatic aldehydes (C1-C3) with arylamines and cyclopentadiene (the Povarov reaction) gave 3a,4,5,9b-tetrahydro-3H-cyclopenta[c]-quinolines. Ozonization of their N-trifluoroacetyl derivatives afforded the corresponding ozonides. Cyclocondensation of 4-fluoroaniline with formaldehyde and cyclopentadiene gave earlier unknown 2-fluoro-3b,6,6a,7,9,9a,10,12a-octahydrobenzo[i,j]dicyclopenta[b,g]quinolizine.

The cerium(IV) ammonium nitrate (CAN)-catalyzed sequential multicomponent reaction between tryptamine, α,β-unsaturated aldehydes, and β-dicarbonyl compounds affords highly substituted indolo[2,3-a]quinolizines in a single synthetic operation. Two rings are generated through the creation of two C-C and two C-N bonds by a domino process comprising initial β-enaminone formation, followed by individual Michael addition, 6-exo-trig cyclization, iminium formation, and Pictet-Spengler steps. Furthermore, the reaction is diastereoselective and affords exclusively compounds with a trans relationship between the H-2 and H-12b protons. The use of amines bearing a less nucleophilic side chain aromatic ring (5-bromotryptamine, 3,4-dimethoxyphenylethylamine) prevents the Pictet-Spengler final step and leads to N-indolylethyl or N-phenylethyl-1,4-dihydropyridines, which are cyclized to the corresponding indolo[2,3-a]quinolizines or benzo[a]quinolizines in the presence of HCl in methanol/water. Treatment of the fused quinolizine derivatives with sodium triacetoxyborohydride led to the corresponding indolo[2,3-a]quinolizidines or benzo[a]quinolizidines, possessing four stereogenic centers, as mixtures of two diastereomers.

Starting from Boc-protected tryptamine and (S)-tetrahydro-5-oxo-2-furancarboxylic acid, facile enantioselective total synthesis of desbromoarborescidines A-C and the formal synthesis of (S)-deplancheine have been accomplished via a common intermediate (S)-indolo[2,3-a]quinolizine. Synthesis of enantiomerically pure (S)-acetoxyglutarimide, stereoselective reductive intramolecular cyclization, hydroxyl group-assisted in situ N-Boc-deprotection, selective deoxygenation of the xanthate ester, and lactam hydrolysis followed by an appropriate exchange of nitrogen regioselectivity in intramolecular cyclization were the decisive steps.

An expedited method was developed for the enantioselective synthesis of dodecahydrobenz[a]indolo[3,2-h]quinolizine containing five contiguous stereogenic centers with high enantioselectivities (99% ee). The methodology comprises a domino organocatalytic double Michael reaction and Pictet-Spengler-lactamization reaction. The structures and absolute configurations of the appropriate products were confirmed by X-ray analysis.

A facile multi-component process for the synthesis of perfluoroalkylated quinolizine derivatives was achieved using various arylidenemalononitriles, pyridine, and methyl perfluoroalk-2-ynoates as starting materials. Moderate yields were obtained under mild condition. The structures of perfluoroalkylated quinolizine derivatives were characterized by means of 1H NMR, 13C NMR, 19F NMR, IR, LRMS and HRMS. Furthermore, the reaction mechanism was proposed.

The cascade oxidative annulation reactions of aryl imidazoles with two molecules of alkynes via multiple C–H activation proceed efficiently in the presence of [Cp*RhCl2]2 and Cu(OAc)2·H2O to give substituted benzo[ij]imidazo[2,1,5-de]quinolizine-based polyheteroaromatic compounds. This method is compatible with various functional groups, which are very useful for further synthetic transformations.