Formal aza-Michael additions to tropone: Addition of diverse aryl- and alkylamines to tricarbonyl(tropone)iron and [(C7H7O)Fe(CO)3]BF4

A formal aza-Michael addition to tropone by way of tricarbonyl(tropone)iron and/or the tetrafluoroborate salt formed via protonation of the complex is reported. Tricarbonyl(tropone)iron smoothly undergoes the direct aza-Michael reaction with unhindered aliphatic amines under solvent free conditions in good yields. Meanwhile, the known cationic complex [(C₇H₇O)Fe(CO)₃]BF₄ (whose reaction with a small number of nucleophiles was previously reported) undergoes addition with an even broader array of amine nucleophiles. Finally, it was discovered that protecting the aza-Michael adduct as a carbamate was necessary for oxidative demetallation of the complex.     

A novel construction of quino-fused tropone skeleton: first synthesis of 12H-benzo[4,5]cyclohepta[1,2-b]quinolin-12-one derivatives

In the present investigation, the incorporation of both quinoline moiety and tropone ring in a molecule frame work in fused form leading to a series of structurally novel and biologically intriguing quinoline/tropone hybrids 12H-benzo[4,5]cyclohepta[1,2-b]quinolin-12-one derivatives has been first achieved through a simple, and economical two-step procedure, involving the one-pot synthesis of (E)-2-(arylvinyl)quinoline-3-carboxylic acids followed by intramolecular Friedel–Crafts acylation reaction using polyphosphoric acid (PPA).     

Oxidation of some alkoxy-cycloheptatriene derivatives: unusual formation of furan and furanoids from cycloheptatrienes

The oxidation of some alkoxy tropone and tropone ketal derivatives with singlet oxygen and m-chloroperbenzoic acid was investigated. In most cases furan and furanoid derivatives were isolated. The structures of the formed products were determined by means of spectral data and the formation mechanism of these unusual products is discussed.     

Theoretical studies on the protonation behavior of tropone and its metal complexes

Density functional theory calculations were carried out to investigate structures and stabilities of tropone and troponeiron complexes, (tropone)Fe(CO)₃, (tropone)Fe(CO)₂(PH₃) and (tropone)Fe(PH₃)₃, and their protonated species. The results show that the oxygen-protonated tropone is more stable than the carbon-protonated tropone. On the contrary, in the troponeiron complexes, the carbon protonated species are more stable than the oxygen protonated species. In the neutral and oxygen-protonated complexes, the tropone and oxygen-protonated tropone ligands are η⁴-coordinated. In the carbon-protonated complexes, the carbon-protonated tropone ligand is η⁵-coordinated. The results also show that the metal shift for complexes containing phosphine ligands is more difficult than that for those containing carbonyl ligands. For the neutral methyl-substituted troponeiron complexes, steric effect was found to play a key role in determining the relative stability of the regioisomers. For their protonated species, the electron-donating properties of the methyl substituent(s) were found to be important in determining the relative stability among the different regioiosmers.     

SCF MO calculations of tropone,tropolone and related compounds

The variable-β procedure of the semiempirical SCF MO method was applied to tropone, tropolone and related compounds. Although the bond alternation in the heptagonal ring is neglected in the initial molecular geometry, the predicted transition energies show a good agreement with experiment, indicating the utility of this method for the calculation of the electronic spectra of non-benzenoid aromatic compounds. Discussions are given on the assignments of the absorption bands of tropone and tropolone.     

Magnetic circular dichroism spectra and electronic spectra of 4,5-benzotropone and thiopheno[c]tropone

Magnetic circular dichroism (MCD) and absorption spectra of 4,5-benzotropone and thiopheno[c]tropone have been measured. The n→π* forbidden transitions of both compounds are assigned by using the theory of Seamans et al. [J. Am. chem. Soc. 94, 6464 (1972)].     

[4 + 2] Cycloaddition reactions of hexachlorotropone

The cycloaddition of hexachlorotropone to selected olefins, including 1,3-dienes, has been examined. Unlike tropone, which undergoes [6 + 4] cycloadditions with 1,3-dienes, only [4 + 2] processes were observed with hexachlorotropone. Its apparent preference for exo-addition (contrast tetrachlorocyclopentadienone) probably results from thermodynamic control of the endo : exo product ratios.     

Nickel-catalyzed skeletal transformation of tropone derivatives via C–C bond activation: catalyst-controlled access to diverse ring systems

We report herein on nickel-catalyzed carbon–carbon bond cleavage reactions of 2,4,6-cycloheptatrien-1-one (tropone) derivatives. When a Ni/N-heterocyclic carbene catalyst is used, decarbonylation proceeds with the formation of a benzene ring, while the use of bidentate ligands in conjunction with an alcohol additive results in a two-carbon ring contraction with the generation of cyclopentadiene derivatives. The latter reaction involves a nickel–ketene complex as an intermediate, which was characterized by X-ray crystallography. The choice of an appropriate ligand allows for selective synthesis of four different products via the cleavage of a seven-membered carbocyclic skeleton. Reaction mechanisms and ligand-controlled selectivity for both types of ring contraction reactions were also investigated computationally.

We report on C–C bond cleavage reactions of tropone derivatives by nickel catalysis. A single tropone derivative can be diversified into four different products with different ring skeletons by the judicious choice of the ligand.     

Some peculiar cases of 7-telesubstitution by anionic phosphorus nucleophiles on 2-halotropones

Both 2-chloro- and 2-fluoro[3,5-²H₃]tropone were found to react with lithium diphenylphosphide in tetrahydrofuran to give 2-diphenylphosphino[4,6-²H₃]tropone in what constitutes the first example of telesubstitution by an anionic nucleophile in a non-protic solvent on tropones carrying nucleofugal groups; lithium diphenylphosphide oxide showed the same behaviour.     

Synthesis and Some Reactions of 2,4,6-Cycloheptatrienethione

The synthesis of 2,4,6-cycloheptatrienethione ( 1 ) was accomplished by reaction of tropone and phosphorus pentasulfide. Although 1 proved to be extremely unstable in concentrated solution, its UV. spectrum was measured, the ε-values being determined indirectly by hydrolysis to tropone. The proof of structure rests on analytical data, conversion to tropone oxime on reaction with hydroxylamine and reaction with the sodium salt of malonitrile to give 2-amino-3-cyano-3aH-cyclohepta[b]thiophene ( 4 ) which rearranged on chromatography to give what is probably the corresponding 8H-compound ( 5 ). On dissolving 1 in 95% sulfuric acid, a large hypsochromic shift in the UV. spectrum was observed, which may be due to the mercaptotropylium ion.     

Synthesis of benzo analogs of oxoarcyriaflavins and caulersine

In the course of a program aimed at designing new antitumor agents, we were interested in the synthesis of mixed structures of maleimidophenyl carbazoles and natural product caulersine as potential CDK inhibitors. This was performed through an efficient four-step sequence starting from indole or 3-formyl-N-Boc indole. 5H-Benzocycloheptaindol-6-one derivatives equipped with a fused maleimide (oxophenylarcyriaflavins) or a methyl ester (benzo analog of caulersine) on the central tropone ring were thus obtained.     

Intermolecular hydrogen bonding as an aid to the preferential exhibition of the smectic C phase in troponoid liquid crystals

Abstract

2-(4-Alkoxybenzoyloxy)-5-alkylaminotropone and 5-alkoxy-2-(4-alkylaminobenzoyloxy)tropone liquid crystals showed the smectic C phase exclusively. Variable temperature FT-IR spectra indicated that intermolecular hydrogen bonding between the NH and tropone C=O groups assisted the appearance of the mesophase. 4-Alkoxyphenyl 4-alkylaminobenzoates were non-mesogenic.     

5,8,11‐Trioxa‐2,14‐di­thia­bi­cyclo­[13.4.1]­icosa‐1(19),15,17‐trien‐20‐one

The title compound, C₁₅H₂₀O₄S₂, crystallizes in a chiral space group although it contains mirror symmetry. The tropone ring is inclined at an angle of 50.3 (1)° to the crown ether ring. The planarity of the tropone ring system itself is diminished by as much as 20.8 (4)°.     

Molecular design by cycloaddition reactions—36: Cycloaddition reactions of 7-azabenzonorbornadiene with troponoid compounds and photochemistry of the adducts

Reactions of 7-azabenzonorbornadiene 1 with tropone, tropolone and 2-aminotropone gave exclusively endo-exo adducts 3a–c in good yields. Similar reaction of other troponoid compounds like 2-acetylamino-, 2-acetoxy- and 2-methoxytropone afforded two isomeric cycloadducts in each case. Photolyses of tropone-adduct 3a in various solvents gave the corresponding cyclopropylcarboxylic acid derivatives 7–11 in high yields. Photochemical behaviors of these adducts 3c, e, f, 5e–f and 4d were also examined.     

On the non-classical course of Polonowski reactions of N-benzylmorpholine-N-oxide (NBnMO)

The Polonowski reaction of NBnMO (4) afforded tropone (10) and the novel isoindole 11 besides the expected products benzaldehyde and acetmorpholide, in a temperature-dependent ratio. The reaction proceeded via two primary carbenium-iminium ion intermediates, an exo-centered species 5 which underwent a benzylium-tropylium type rearrangement, and a ring-centered species 6, which reacted further to isoindole 11 by intramolecular electrophilic substitution. The experimental findings were in good agreement with DFT computational data.     

The cycloaddition reaction of 3,4-dimethyl-1-thio-1-phenylphosphole with tropone

3,4-Dimethyl-1-thio-1-phenylphosphole reacts, under elevated temperatures, with tropone to give two [4+2] isomeric adducts: Endo-syn-5,6-dimethyl-3-thio-3-phenyl-3-phosphatricyclo [5.3.2.0^2,6]dodec-4,8,11-trien-10-one (1) and Endo-anti-5,6-dimethyl-3-thio-3-phenyl-3-phosphatricyclo[5.3.2.0^2,6]dodec-4,9,11-trien-8-one (2). In addition to the endo-exo,syn-anti relationship the phosphorus configuration in 1, 2 and some derivatives was also elucidated by means of NMR-shift reagents and ²J_PH coupling constants.     

Semi-Synthesis of Harringtonolide Derivatives and Their Antiproliferative Activity

Harringtonolide (HO), a natural product isolated from Cephalotaxus harringtonia, exhibits potent antiproliferative activity. However, little information has been reported on the systematic structure−activity relationship (SAR) of HO derivatives. Modifications on tropone, lactone, and allyl positions of HO (1) were carried out to provide 17 derivatives (2–13, 11a–11f). The in vitro antiproliferative activity against four cancer cell lines (HCT-116, A375, A549, and Huh-7) and one normal cell line (L-02) was tested. Amongst these novel derivatives, compound 6 exhibited comparable cell growth inhibitory activity to HO and displayed better selectivity index (SI = 56.5) between Huh-7 and L-02 cells. The SAR results revealed that the tropone and lactone moieties are essential for the cytotoxic activities, which provided useful suggestions for further structural optimization of HO.     

Highly contorted superhelicene hits near-infrared circularly polarized luminescence

Herein we describe a novel superhelicene structure consisting of three hexa-peri-hexabenzocoronene (HBC) units arranged in a helical geometry and creating two carbo[5]helicenes and a carbo[7]helicene. The central HBC bears a tropone moiety, which induces a saddle-helix hybrid geometry into the 3D structure of the prepared nanographene. The introduction of multiple helicenes and the position of the tropone unit trigger near-infrared circularly polarized luminescence (NIR-CPL, up to 850 nm, |g_lum| = 3.0 × 10⁻³) combined with good photoluminescence quantum yields (ϕ_F = 0.43) and upconverted emission based on two-photon absorption (TPA). Compared to previously reported superhelicenes of similar size, higher quantum yields, CPL brightness, and red-shifted absorption and emission spectra are achieved. Besides, chiroptical properties of enantiopure thin films were evaluated. These findings place this novel superhelicene as the first NIR-CPL superhelicene ever reported and make it a promising candidate for use as a chiral luminescent material in optoelectronic devices.

This twisted superhelicene employed its twists and loops to shine chiral emission into the NIR region. The proof of its promising applicability in optoelectronic devices is the analogous chiroptical properties obtained in solution and thin films.     

Effects of benzoyl group substituents on the mesomorphic properties of 5-alkoxy-2-benzoylaminotropones

Three types of 5-alkoxy-2-benzoylaminotropones, containing an electron-donating group and seven types of derivatives with electron-withdrawing groups on the benzoyl group, were prepared in order to study the thermal ranges of the mesophases exhibited. The troponoid amides had higher transition temperatures than the corresponding troponoid esters and benzenoid amides. From the ¹H NMR spectroscopic measurements and X-ray crystallographic analysis of 5-butoxy-2-(4-methoxybenzoylamino)tropone, it was observed that the benzoyl carbonyl group faced to the H-3 of the tropone ring to form an intramolecular hydrogen bond between the tropone carbonyl and the amide NH groups. The intramolecular hydrogen bonding of the troponoid amides made the molecules flat, inducing strong π–π intermolecular interactions between head-to-tail dimers and so reduced the possibility of intermolecular hydrogen bonding between the NH group and the carbonyl group of neighbouring molecules so decreasing melting points. Electron-donating groups enhanced the appearance of nematic phases while electron-withdrawing groups promoted smectic A phases.     

Hydroxytropylium chloride: the first crystal structure of an unfunctionalized hydroxytropylium ion

The crystal structure of hydroxytropylium chloride, C₇H₆OH⁺·Cl⁻, the hydrochloride salt of tropone, is described, which represents the first crystallographic characterization of an unfunctionalized hydroxytropylium ion. Crystals were obtained serendipitously from a sample of chlorotropylium chloride after partial hydrolysis. This highlights the role of hydroxytropylium ions as an intermediate in the hydrolytic decomposition of halotropylium halides to tropone. The solid‐state structure consists of layers, in which the hydroxytropylium and chloride ions interact via both strong hydrogen bonds formed by the hydroxy protons and weaker hydrogen bonds formed by the tropylium protons to produce a two‐dimensional network.