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π-Expanded homoHPHACs with thiocarbonyl and carbonyl bridges change their global aromaticity in response to external stimuli as observed in tropothione and tropone.

Here we report a highly stable 16π-electron antiaromatic system based on the ligand-oxidized Cu(ii)-tetrabenzocorrole. The antiaromaticity of the monocationic corrole complex was elucidated with the unique bond length alternation pattern of the crystal structure and the spectral diagnostic features. The NICS and GIMIC calculations clearly depicted its inner 15-membered-ring main pathway with a strong paratropic ring current.

Benzene-fused bis(acenaphthoBODIPY)s prepared by retro-Diels–Alder reaction of bicyclo[2.2.2]octadiene-fused precursors showed strong absorption bands in the near-infrared region and very weak absorptions in the visible region.

A kinetic study on radical cascade reactions of 1,6-enyne compounds was undertaken. The efficiency of the reaction depended on the presence of an ester group at the alkene unit, which clearly suggests that the addition of a tin radical was accelerated by the α,β-unsaturated system. Stannolane formation progressed very quickly after a short induction period and completed within 12 min in the presence of Bu3SnH at 10−2 M concentration at 110 °C. Product ratios between stannolane and exo-methylene compound depended on the concentration of Bu3SnH; a linear relationship was observed between the ratios of the two and the concentration of Bu3SnH. These results clearly indicate that the SHi process is irreversible. The slope of the graph allowed us to estimate the ks value, the SHi reaction rate at the tin atom, as 4.23 × 108 s−1 at 303 K. The use of Bu2PhSnH for the reaction suggests that the SHi process partially progresses by the frontside attack of the vinyl radical, which generates a methylene radical that undergoes neophyl rearrangement to give methylene piperidine in a cis-selective manner.

Bicyclo[2.2.2]octadiene-fused (BCOD-fused) bis(benzoborondipyrromethene)s (bisbenzoBODIPYs) bearing electron-withdrawing groups such as fluorine and cyano groups were prepared either by incorporating tetrafluoroisoindole moieties into BODIPY chromophores or by introducing cyano or ethoxycarbonyl groups at the 3,5-positions. The BCOD-fused bisbenzoBODIPYs were quantitatively converted to the corresponding benzene-fused bisbenzoBODIPYs by a retro-Diels-Alder reaction. The π-fused bisbenzoBODIPYs were found to have intense absorption in the near-infrared region and not to have any strong absorption bands in the visible region. Moreover, the bisbenzoBODIPYs were stable under atmospheric conditions.

The synthesis and crystal structure of a zirconocene derivative with α-Keggin mono-aluminum-substituted polyoxotungstate, [α-PW(11)Al(OH)O(39)ZrCp(2)](2)(6-) (Cp = C(5)H(5)(-)) (1), which was obtained by the reaction of α-Keggin mono-aluminum-substituted polyoxotungstate with a biscyclopentadienylzirconium(IV) complex, is described herein. Analytically pure, homogeneous, yellow crystals of the tetra-n-butylammonium salt of polyoxoanion 1, [(n-C(4)H(9))(4)N](6)[α-PW(11)Al(OH)O(39)ZrCp(2)](2) (TBA-1), were obtained from the ca. 1 : 1 reaction of [(n-C(4)H(9))(4)N](4)[α-PW(11){Al(OH(2))}O(39)] with Cp(2)Zr(OTf)(2)·THF (OTf = O(3)SCF(3)(-)) in acetonitrile solution under an argon atmosphere, followed by precipitation from water and crystallization from acetonitrile. TBA-1 was characterized based on X-ray structure analysis, elemental analysis, thermogravimetric/differential thermal analysis (TG/DTA), Fourier transform infrared (FTIR), and solution ((31)P, (27)Al, (19)F, (1)H, and (13)C) nuclear magnetic resonance (NMR) spectroscopy. Single-crystal X-ray structure analysis revealed that the two {PW(11)AlO(40)} units are bridged by two "bent sandwich" Cp(2)Zr(2+) fragments with C(2) symmetry. Each zirconium center was bound to a terminal oxygen atom of the aluminum and tungsten sites and an edge-sharing oxygen atom at the Al-O-W linkage. Further, the stability towards water was investigated by NMR ((31)P, (1)H, and (13)C) and FTIR spectroscopy. The η(5)-cyclopentadienylzirconium fragments were not eliminated from the surface of [α-PW(11){Al(OH(2))}O(39)](4-) even after 24 h exposure to 50 equiv. of water.

Acid-catalyzed oligomerization of 2-(hydroxymethyl)pyrroles bearing C6F5, 2,6-Cl2C6H3, CF3 and CO2Et groups at beta-positions was examined. The reaction of ethyl pyrrole-3-carboxylates gave a mixture of oligomers and type I isomers of porphyrinogens and hexaphyrinogens were isolated when the other beta-substituents were sufficiently bulky, for example, mesityl, 2,6-Cl2C6H3 and C6F5 groups. On the other hand, the pyrroles having other electron-withdrawing groups afforded porphyrinogens as the only isolable products.

The metal-free and meso-free [14]triphyrin(2.1.1) compound was successfully prepared based on the intramolecular McMurry coupling reaction of diformyl-tripyrrane in 16% yield, and was converted to the bowl-shaped Mn(I)(TriP)(CO)(3) and Re(I)(TriP)(CO)(3).

Intramolecular condensation of 2-(acetonyl)-3-acyljuglone derivatives under basic conditions gave 1,6- and/or 1,8-dihydroxyanthraquinones depending on the conditions employed. Treatment of 6-[(3-acetyl-5-methoxy-1,4-dioxo-1,4-dihydro-2-naphthyl)methyl]-2,2-dimethyl-4H-1,3-dioxin-4-one with K2CO3 in alcohol brought about the intramolecular Knoevenagel-type reaction to give 3-hydroxy-8-methoxy-1-methyl-9,10-dioxo-9,10-dihydro-anthracene-2-carboxylates in good yields, while the same naphthoquinone gave 4-hydroxy-5-methoxy-9,10-dioxo-9,10-dihydroanthracene-2-acetic acid in good yield by treatment with potassium bis(trimethylsilyl)amide (KHMDS). Chrysophanol, aloe-emodin, aloesaponarin I, and K1115A were prepared in good yields.

Regioselective halogenation of 3-acetoxymethyl-7-chloro-5,8-dimethoxy-1-naphthol 5 was achieved by DBH or I2/N-methylmorpholine to give the corresponding 2-halogeno-1-naphthols 8 and 11, which were converted to 1-methoxymethoxy-3-(alk-2-ynoyloxymethyl)-2-halogenonaphthalenes 17 and 18 in good yields. An intramolecular acyl-transfer reaction of the 2-halogenonaphthalenes triggered by halogen–lithium exchange with BuLi at −78 °C gave 1-methoxymethoxy-2-alkynoyl-3-(hydroxymethyl)naphthalenes 21 in high yields. After protection of the hydroxymethyl group as a benzoate, formation of a γ-pyrone ring was easily achieved by deprotection of the methoxymethyl group followed by spontaneous 6-endo ring closure under mildly acidic conditions. The pyrone derivative having a 1-methylpropyl group was successfully converted to espicufolin 1.

Stable 2H-isoindoles with electron-withdrawing groups were prepared using the reaction of dinitrobenzene derivatives with isocyanoacetate in the presence of DBU. The use of acetonitrile as the solvent or a phosphazene base (BTPP) as a non-ionic base improved the yields. The structure was confirmed by X-ray crystallographic analysis of the compound 2e′. According to the X-ray analysis, this substance existed in the solid phase only as the 2H-isomer.

Ethyl 4-formylpyrrole-2-carboxylates were prepared from nitroacetaldehyde dimethyl acetal in 9–50% yields using the Barton–Zard reaction. These formylpyrroles were successfully transformed to cycloalkano-oligopyrroles. The conformation of cyclononatripyrroles in CDCl3 was found to be a crown form based on the NMR analysis, while cyclododecatetrapyrroles were in two interconverting boat and chair conformations.

Three series of dimers containing pyrrolo[3,4-e][2,1,3]benzothiadiazole units have been prepared by application of the Pd-catalyzed Suzuki coupling. The dependence of the HOMO–LUMO separation on coplanarity has been evaluated by means of electronic absorption spectra and cyclic voltammetry. The pyrrole dimer 5c shows a narrow HOMO–LUMO separation owing to its intrinsically planar structure, as confirmed by 1H NMR.

Pyrroles fused with bicyclo[2.2.2]octene and bicyclo[2.2.1]heptene frameworks are prepared by a modified Barton–Zard method. Structures of these pyrroles and thermal behaviours of the former pyrroles are studied by X-ray and DSC analyses.

The regioselectivity in the ruthenium-catalysed allylic alkylation of mono substituted allyl acetates with the malonate anion was highly controlled by Ru3(CO)12 with 2-(diphenylphosphino)benzoic acid, and the linear-type alkylated product was obtained.

5-Alkenyl-15-alkynylporphyrins have been obtained unexpectedly by [2 + 2] acid-catalyzed condensation of dipyrrylmethane and TMS propynal in addition to 5,15-dialkynylporphyrin, and the unsymmetrical porphyrin can be converted to a butadiyne-linked dimer by selective desilylation of the alkynyl TMS.

Ethyl 12-oxo-4,11-dihydro-4,11-ethanonaphth[2,3-f]isoindole-1-carboxylate (2) was prepared from 7-tert-butoxynorbornadiene and quantitatively converted to ethyl naphth[2,3-f]isoindole-1-carboxylate (3) by the thermal or photochemical cheletropic reaction. Ethyl naphth[2,3-f]isoindole-1-carboxylate (3) existed in a 2H-form both in solution and as a solid, and gradually dimerized to give a dianthradiazafulvalene derivative under aerobic conditions.

The non-luminous precursor, 2-(1-pyrenyl)-9,10-dihydro-9,10-ethanoanthracene-11,12-dione, was photochemically converted to highly-fluorescent 2-(1-pyrenyl)anthracene quantitatively in solution and in the PMMA film and the fluorescence quantum yield of the acene in benzonitrile was as high as 0.99.

o-Quinodimethane (o-QDM) generated from benzosultine was used to extend the pyrrole system for the preparation of octabromo-tetranaphtho[2,3]porphyrins via oxidative aromatization. The properties of these bromoporphyrins were presented and chemical transformation via Pd-catalyzed Suzuki reaction was also effectively achieved.

Peripherally π-extended N-confused porphyrin rhenium complexes were synthesized by the rhenium-mediated reactions of N-confused porphyrins with 2-methyl azaarene and the structures were elucidated by X-ray crystallographic analyses. Extension of the π-conjugation in the complexes was supported by the absorption spectra, electrochemical measurements and theoretical calculations.

Porphyrin dimers were prepared from β,β′-dipyrrole derivatives via the double pyrrolylmethylation followed by double [2+2] MacDonald porphyrin synthesis.

A soluble porphyrin dimer linked with bicyclo[2.2.2]octadiene was converted into insoluble conjugated porphyrin dimer by heating at 200 °C, this provides a new strategy for the process control of conjugated porphyrins.

A new α-diketoporphyrin and the corresponding Pd complex were prepared from the monoanthroporphyins and their photochemical properties were investigated by measurements of absorption and emission spectra, fluorescence lifetimes, laser flash photolysis, cyclic voltammetry, and theoretical calculations. Intramolecular electron transfer from the porphyrin singlet excited state to the diketone moiety was observed for the free base α-diketoporphyrin in benzonitrile, but this was not observed in toluene. Photoreactivity of the α-diketoporphyrins was also examined by irradiation at the Soret and Q bands. When the Soret band of the freebase α-diketoporphyrin was irradiated, cleavage of the diketone moiety occurred to afford the monoanthroporphyrin with the release of two CO molecules quantitatively in both benzonitrile and toluene. When the Q band of the freebase α-diketoporphyrin was irradiated, no photocleavage reaction occurred in toluene. In contrast to the freebase α-diketoporphyrin, the photocleavage reaction of the Pd complex occurred with irradiation at the Q band as well as the Soret band to afford the monoanthroporphyrin quantitatively in toluene. The photocleavage reaction proceeded much more effectively in toluene than in benzonitrile. The occurrence of rapid photoinduced electron transfer from the singlet excited state porphyrin to the diketone moiety, which was detected by femtosecond laser flash photolysis measurements, results in a significant decrease in the singlet excited state lifetime, prohibiting the photocleavage reaction in benzonitrile. Thus, the Pd α-diketoporphyrin can act as an excellent precursor for the corresponding acene in toluene. The photocleavage process provides a convenient and inexpensive method to make the thin film.

A new synthesis of [2,3]naphthoporphyrins using 4,9-ethano-2H-benz[f]isoindole as a synthon of 2H-benz[f]- isoindole is described; soluble precursors of [2,3]naphthoporphyrins are converted into insoluble [2,3]naphthoporphyrins by simply heating at 290 °C.

Pt(II) complex of meso-tetrakis(pentafluorophenyl) N-confused porphyrin (1-Pt) efficiently binds Cl(-), Br(-), and I(-) anions at the peripheral N-H, while deprotonation proceeds with F(-), H(2)PO(4)(-), and OH(-) in CH(2)Cl(2) solution; neutral and anionic structures of 1-Pt were characterized by single crystal X-ray diffraction analysis.

Porphyrins fused with bicyclo[2.2.2]octene frameworks are prepared; the bicyclo[2.2.2] units rigidify the porphyrin ring to maintain planar conformations in solution.

Heating 4,7-dihydro-4,7-ethano-2H-isoindole at 200 °C induces the retro-Diels–Alder reaction to give isoindole in essentially quantitative yield, which can be applied to a new synthesis of tetrabenzoporphyrins and monobenzoporphyrins.

Enlargement of the pi-electronic network of meso-meso, beta-beta, beta-beta triply linked diporphyrin has been exploited by preparing a corresponding dibenzo-fused porphyrin dimer that exhibits a perturbed absorption spectrum and a large two-photon absorption cross section.

The boron trifluoride-catalyzed Rothemund condensations of phenylpropargylaldehyde with 4,7-dihydro-4,7-ethano-2H-isoindole or 3,4-diethylpyrrole in dichloromethane at low temperature give 5,10,15,20-tetrakis(phenylethynyl)porphyrins bearing bicyclo[2.2.2]octadiene and octaethyl substituents, respectively. The former undergoes a retro Diels-Alder reaction to afford 5,10,15,20-tetrakis(phenylethynyl)benzoporphyrin quantitatively. The different conformations of the porphyrin periphery were determined by X-ray diffraction and their redox and spectroscopic properties have been investigated.

(±)-Eleutherin (1) and (±)-isoeleutherin (3) are prepared by intramolecular cyclization to the naphthopyrans of 2-acetyl-3-allyl-8-methoxy-1, 4-napthoquinone, which is itself obtained by the Lewis acid-mediated allylation of 2-acetyl-8-methoxy-1, 4-naphthoquinone (5) with allyltrimethylstannane (7).

The Lewis acid-promoted reaction of 1-nitroalka-1,5-(or 1,6-)dienes with allylic stannanes has been studied. In the presence of TiCl4, 1-nitrohexa-1,5-diene reacted smoothly with allyltrimethylstannane to give a diastereoisomeric mixture of 6-allyl-3a,4,5,6-tetrahydro-3H-cyclopent[c] isoxazoles, while the reaction using AlCl3 as catalyst led to an allylated cyclohexanone oxime derivative in good yield. The similar reaction of 1-nitrohepta-1,6-diene, however, gave a bicyclic dihydroisoxazole irrespective of the Lewis acids employed. In the latter case, nitrite oxide equivalents derived from 1-nitroalka-1,6-dienes underwent a stepwise cycloaddition as shown by the lack of stereospecificity in the reactions of (1E,6Z)-1-nitro-7-phenylhepta-1,6-diene and (1E,6Z)-1-nitro-octa-1,6-diene.