Benzo- and indoloquinolizine derivatives—V : A novel route to 6,7-dihydrodibenzo[a,f]quinolizinium salts and to 1,2,3,4,10,11-hexahydrotribenzo[a,c,h]quinolizinium salts

The reaction between paraldehyde, acetone or cyclohexanone, and 2 - phenyl - 3,4 - dihydroisoquinolinium salts gives rise to 6,7 -dihydrodibenzo[a,f]qu salts and 1,2,3,4,10,11 -hexahydrotribenzo[a,c,h]quinolizinium salts.     

Synthesis and reactions of methylbenzo[c]quinolizinium salts

Six isomers of the methylbenzo[c]quinolizinium salt 3 including four new monomethyl derivatives were synthesized by thermal-intramolecular quaternization of the cis-methyl-substituted 2-[2-(2-chlorophenyl)-vinyl]pyridines 4 or by the irradiation of trans- 4 with selected wavelengths (290 < λ < 340 nm and λ > 400 nm) in acetonitrile. Among the regioisomeric monomethyl derivatives 3 , the 1-, 3-, and 6-methyl derivatives 3b, 3d , and 3g reacted with p-methoxybenzaldehyde in the presence of bis(l-piperidino)-(p-methoxyphenyl)-methane 7 to yield trans-(p-methoxystyryl)benzo[c]quinolizinium salts 6 . The reactivity of 3 and methylbenzo[a]quinolizinium salts 1 was discussed on the basis of their π-electron energy.     

The electrochemistry of benzo[b]quinolizinium ion

Summary In aprotic solvents, polarography and cyclic voltammetry indicate a two step reduction of acridizinium ion. The first reduction is a reversible one-electron step. The second involves two electrons and is irreversible. In situ ESR electrolysis at the potential of the first reduction gives no evidence of free radicals. Homogeneous chemical reduction of acridizinium by titration with sodium biphenylide indicates a one-electron reduction mechanism in solution. The absence of stable free radicals suggests a rapid post-reduction of the product.Addition of small amounts of water changes the aprotic solvent (mercury electrode) mechanism. The first wave becomes a two-electron irreversible wave at the expense of the second wave. In aqueous solvents two two-electron, irreversible reduction waves occur. Products of the second absorb and change the mechanism after the first CV scan.

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Elektrochemisches Verhalten des Benzo[b]chinolizinium-Ions

Zusammenfassung In aprotischen Lösungsmitteln wird durch Polarographie und cyclische Voltammetrie eine zweistufige Reduktion des Acridizinium-Ions angezeigt. Die erste Stufe ist reversibel und bezieht sich auf ein Elektron, die zweite Stufe umfaßt 2 Elektronen und ist irreversibel. Durch in situ ESR-Elektrolyse beim Potential der ersten Stufe konnte kein Beweis für freie Radikale gefunden werden. Homogene chemische Reduktion durch Titration mit Natriumbiphenylid deutet auf einen einelektronigen Reduktionsmechanismus hin. Durch Zugabe kleiner Wassermengen wird die erste Stufe auf Kosten der zweiten irreversibel und zweielektronig. In wäßrigen Lösungsmitteln treten 2 zweielektronige irreversible Reduktionsstufen auf.

     

Synthesis and reaction of methylbenzo[a]quinolizinium salts

All isomers of (monomethyl)benzo[a]quinolizinium salts including five new monomethyl derivatives were prepared by photocyclization, sulfur extrusion, or cyclodehydration reaction, and their aldol-type condensation was examined. The 2- and 4-methyl derivatives 3b and 3c reacted with p-methoxybenzaldehyde in the presence of piperidine to yield trans-(p-methoxystyryl)benzo[a]quinolizinium salts 11 . The other methyl derivatives did not react with the aldehyde. The methyl group was reactive at the 2- and 4-positions, located para and ortho to the azonia ring nitrogen, respectively; however, it was unreactive at the 6-position located at another ortho position.     

Efficient functionalization of quinolizinium cations with organotrifluoroborates in water

An efficient functionalization of the quinolizinium system is reported. The reaction of the four isomeric bromoquinolizinium salts with different organotrifluoroborates afforded alkyl-, vinyl-, aryl-, and heteroaryl quinolizinium derivatives in moderate or good yields. Reactions are carried out in water using a counterion exchange for the isolation of the cationic-coupled compounds.     

Fluorimetric detection of Mg2+ and DNA with 9-(alkoxyphenyl)benzo[b]quinolizinium derivatives

A benzo[b]quinolizinium-benzo-15-crown-5 ether conjugate 2a is presented that enables the fluorimetric detection of Mg(2+) and DNA by a significant light-up effect, along with a change of the emission wavelength with different analytes (Mg(2+): 495 nm; DNA: 550 nm). The mechanism of the excited-state deactivation of 2a was investigated by steady-state fluorescence spectroscopy in media of varied viscosity and compared with the photophysical properties of methoxyphenyl-substituted benzo[b]quinolizinium 2b (m,p-diOMe), 2c (m-OMe), and 2d (p-OMe) as reference compounds. Compounds 2a-c, which share the m-alkoxyphenyl substituent as the common feature, have low emission quantum yields (Φ(F) < 10(-2) in water) but exhibit a significant increase of their fluorescence intensity in viscous glycerol solutions. In contrast, the viscosity of the medium does not influence the emission properties of the parent phenyl-substituted benzo[b]quinolizinium 2e and of the p-methoxyphenyl-substituted derivative 2d. Based on these observations it is concluded that the excited-state deactivation in 2a-c is mainly due to the rotation of the m-alkoxy group about the C(ar)-O bond. The interaction of 2a-c with DNA or Mg(2+) ions was studied by spectrophotometric titrations and CD spectroscopy. Notably, the association of 2a or 2b with DNA or 2a with Mg(2+) ions induces a strong fluorescence enhancement (15- and 40-fold for DNA, 450-fold for Mg(2+)), which is rationalized by the suppression of the torsional-relaxation of the alkoxy-substituent in the excited state. Additionally, the cation-induced light-up effect of 2a is selective towards Mg(2+) ions as compared with other cations such as NH(4)(+), Li(+), Na(+), K(+) and Ba(2+).     

13C NMR spectra of some monosubstituted quinolizinium bromides

Chemical shifts are reported for quinolizinium bromide and 12 monosubstituted derivatives, carrying a bromohydroxy, diethylamino or piperidino group as the substituent. In addition, ¹J(CH) values and long-range coupling constants are given.     

The influence of solvent polarity and viscosity on fluorescence of quinolizinium salts

The effects of dielectric constant, viscosity and polarity of the solvents used on the relative fluorescent emission of 2,3-diphenylquinolizinium bromide and 2(p-dimethyl-amino)styryl-3-methylquinolizinium bromide are described. These salts were entirely dissolved in ten different solvents. The 2(p-dimethylamino)styryl derivative produced different ionic species, and was a fluorescent acid-base indicator. The fluorescence of these quinolizinium salts is shown to increase with greater viscosity of the medium.     

A unified approach to quinolizinium cations and related systems by ring-closing metathesis

[reaction: see text] The first example of an olefin ring-closing metathesis reaction on cationic heteroaromatic systems is described. Dihydroquinolizinium cations and a variety of related cationic systems are synthesized in an efficient approach from N-alkenyl alpha-vinyl azinium salts using Grubbs' catalysts.     

Synthesis and structural, spectroscopic, and electrochemical characterization of benzo[c]quinolizinium and its 5-aza-, 6-aza, and 5,6-diaza analogues

Four heterocyclic salts 1a-d were prepared by Ca²⁺-assisted cyclization of fluoro derivatives 3, and investigated by spectroscopic (NMR and UV), electrochemical, and computational (DFT and MP2) methods. The mechanism for the formation of the cations was investigated at the DFT level of theory. 2-D NMR spectroscopy for 1[ClO₄] in DMSO­d₆ aided with DFT results permitted the assignment of ¹H and ¹³C NMR signals in cations 1. The molecular and crystal structures for 1a[ClO₄] [C₁₃H₁₀ClNO₄ triclinic, P−1, a=9.6517(12) Å, b=11.0470(13) Å, c=12.2373(15) Å, α=67.615(1)°, β=78.845(2)°, γ=87.559(2)°; V=1183.0(2) Å³, Z=4] and 1d[ClO₄] [C₁₂H₉ClN₂O₄ triclinic, P−1, a=5.9525(6) Å, b=8.3141(9) Å, c=12.2591(13) Å, α=73.487(1)°, β=83.814(1)°, γ=83.456(1)°; V=576.07(10) Å³, Z=2] were determined by X-ray crystallography and compared with results of DFT and MP2 calculations. Electrochemical analysis gave the reduction potential order (1b>1c∼1d>1a), which is consistent with computational results.     

Palladium-mediated functionalization of heteroaromatic cations: comparative study on quinolizinium cations

An efficient palladium-catalyzed cross-coupling reaction on heteroaromatic cations is described. A comparative study of the Stille and Suzuki reactions shows that only the Stille reaction is able to produce an efficient C-C bond formation between any of the four isomeric bromoquinolizinium bromides and a variety of stannanes. In the presence of the catalysts Pd(PPh3)4 or Pd2(dba)3P(o-Tol)3, vinyl, ethynyl, aryl, and heteroaryl groups are successfully incorporated into the quinolizinium system in satisfactory yields under mild reaction conditions. This procedure represents a marked improvement on the functionalization of this class of heteroaromatic cation.     

Reissert compound studies. XXXVI. Observations on 1,7-, 4,6-, 4,7-, and 1,10-phenanthrolines

Reissert compounds have been prepared from 1,7-, 4,6-, and 4,7-phenanthrolines. In the case of 4,7-phenanthroline, both mono- and di-Reissert compounds have been prepared. A number of Reissert analogs have also been prepared in this series. 1,10-Phenanthroline fails to give a Reissert compound.