Takahisa Machiguchi

Tropothione. Synthesis, spectra and chemical reactions

Abstract Tropothione has been effectively synthesized as unstable red crystals and fully characterized by various spectroscopies as well as pKa and dipole moment measurements together with chemical characterization reactions. The properties of tropothione was revealed to differ considerably from those of tropone.

A Facile and Efficient Preparation of Tropone from Di-7-Cycloheptatrienyl Ether Using Trifluoroacetic Acid as a Catalyst

Abstract Tropone is prepared by an improved method in high yields without troublesome workup processes. Thus, di-7-cycloheptatrienyl ether is treated at room temperature with a small amount of trifluoroacetic acid as a catalyst.

SYNTHESIS AND ISOLATION OF TROPOTHIONE : A COMPARATIVE STUDY OF SPECTRAL PROPERTY WITH TROPONE

Abstract The synthesis, isolation, and spectral characterization of tropothione (1), the sulfur analogue of tropone (2), are described with comparison of those for 2. Direct sulfurization of 2 with tetraphosphorous decasulfide using triethylamine as a catalyst yields the titled compound 1 in high yield. Although 1 is thermally unstable material [ t 1 2 (crystalline state, 0 °C) 56 min], dilute solutions are found to be sufficiently stable enough for measuring spectral data [ t 1 2 (0.01 mol/L, 25 °C) 10.4 days]. The compound 1 is isolated as a labile material of deep red crystals with the melting range of 20–21 °C. IR spectrum of 1 exhibits a very strong band of the vC=S stretching vibration at 1087 cm−1 in CCl4. Raman spectrum supports the assignment. UV-visible spectra in six solvents show three transitions at around 225 (log e ca. 4), 253 (ca. 4), and 380 nm (ca. 4.2), while 1 exhibits an additional weak absorption of n −π ∗ transitions at 610 nm (log e 1.62). 1H NMR of 1 shows wide signals of symmetrical AA′BB′XX′ pattern comprising with a large downfield part of α-protons in the ring due to the magnetic anisotropy of the CS group greater than that of CO one in 2. 13C NMR of 1 displays three doublet signals (δ 131.48, 138.36, and 153.80) accompanying with the singlet one at δ 213.83 (C=S). 33S NMR of 1 exhibits δ − 287 as the first measurement for thiocarbonyl compounds. These physical properties of 1 are in sharp contrast to those of 2.

Solid-state thiotropolone: an extremely rapid intramolecular proton transfer.

Through variable-temperature solution-state NMR and molten- and solid-state CP/MAS (13)C NMR spectra, thiotropolone is found to exist as two rapidly equilibrated tautomeric structures, thione and enethiol, even in the solid state far below the melting point. The crystal structure shows an almost perpendicular packing, suggesting that the intramolecular hydrogen bond is dominant.

TROPOTHIONE VERSUS TROPONE : A COMPARISON OF THE CHARGE SEPARATION IN THE GROUND STATE

Abstract The electric dipole moment of tropothione ( 1 ), a thiocarbonyl compound, and tropone ( 2 ), a carbonyl one, has been compared. The charge separation of 1 and 2 is evaluated on the basis of the dipole moment and ab initio calculations. The dipole moment (μ) of 1 is measured to be 4.42 D in carbon tetrachloride at −15°C and is larger than that ( μ = 3.71 D) of 2 . Ab initio molecular orbital calculations have reproduced these values well and have revealed the origin of this difference.

A phenyl-group participation in the antisymmetric orbital interaction for [8 + 2] cycloaddition of tropothione with diphenylketene

Reaction of tropothione (1) with diphenylketene (2) gives regiospecifically an [8 + 2] cycloadduct (3) in high yield. Twisted phenyl groups in 2 intermix two vacant FMOs of the ketene moiety. This mixing brings about an appropriate site for the antisymmetric orbital interaction against the HOMO of 1. A phenyl carbon is found to assist this interaction.

Experimental and Theoretical Analyses of Azulene Synthesis from Tropones and Active Methylene Compounds: Reaction of 2-Methoxytropone and Malononitrile

A representative azulene formation from an active troponoid precursor (2-methoxytropone) and an active methylene compound (malononitrile) has been analyzed both experimentally and theoretically. (2)H-Tracer experiments using 2-methoxy[3,5,7-(2)H(3)]tropone (2-d(3)) and malononitrile anion give 2-amino-1,3-dicyano[4,6,8-(2)H(3)]azulene (1-d(3)) in quantitative yield. New and stable (2)H-incorporated reaction intermediates have been isolated, and main intermediates have been detected by careful low-temperature NMR measurements. The detection has been guided by mechanistic considerations and B3LYP/6-31(+)G(d) calculations. The facile and quantitative one-pot formation of azulene 1 has been found to consist of a number of consecutive elementary processes: (a) The troponoid substrate, 2-methoxytropone (2), is subject to a nucleophilic substitution by the attack of malononitrile anion (HC(CN)(2)(-)) to form a Meisenheimer-type complex 3, which is rapidly converted to 2-troponylmalononitrile anion (5). (b) The anion 5 is converted to an isolable intermediate, 2-imino-2H-cyclohepta[b]furan-3-carbonitrile (6), by the first ring closure in the reaction. (c) A nucleophilic addition of the second HC(CN)(2)(-) toward the imine 6 at the C-8a position produces the second Meisenheimer-type adduct 7. (d) The second ring closure leads to 1-carbamoyl-1,3-dicyano-2-imino-2,3-dihydroazulene (11). A base attacks the imine 11, which results in generation of a conjugate base 12 of the final product, azulene 1.

Norcaradiene intermediates in mass spectral fragmentations of tropone and tropothioneElectronic supplementary information (ESI) available: reaction paths supporting Figs. 3–6. See http://www.rsc.org/suppdata/p2/b1/b102127n/

The fragmentation of mass spectroscopy of tropone (1) was compared with that of tropothione (2). The electron-impact mass spectroscopy of 1 afforded almost exclusively the benzene cation radical (m/z = 78). Mass spectroscopy of 2 gave similarly the m/z = 78 base peak along with an unusual (M+ − 1) peak. This hydrogen elimination was found to occur at the C(α)–H bond by the use of a 2H-labeled analogue of 2. Ab initio calculations (UB3LYP/6-31G*) showed that a π cation radical of 1 and a σ cation radical of 2 were converted to norcaradiene intermediates. Their further isomerizations led to [the benzene cation radical (m/z = 78) + CO] and [(m/z = 78) + CS], respectively. The fragmentation channel of 1 was calculated to have sufficiently small activation energies of intervening transition states to give almost exclusively the m/z = 78 peak. For a σ radical of 2, an α hydrogen moved to the sulfur atom. The resultant thiol was isomerized to a second norcaradiene and its further isomerization led to a thioketene like cation and a hydrogen atom corresponding to the unusual (M+ − 1) peak. The difference in fragmentation patterns of 1 and 2 is discussed in terms of their electronic structures.

Tropone versus tropothione. Theoretical and experimental analyses of cycloadditions with maleic anhydride

Abstract Ab initio calculations on transition states and products of title reactions were performed. Possible [4+2] and [8+2] reaction paths were investigated. In the tropone ( 1 )-anhydride reaction, the [4+2] endo path was calculated to be best both kinetically and thermodynamically. The distinct selectivity of the [4+2] endo path over the [4+2] exo one was explained in terms of the secondary orbital interaction. In the tropothione ( 2 )-anhydride reaction, the [8+2] endo path, although thermodynamically the second worst, is best kinetically. The difference of the [4+2] or [8+2] selectivity is ascribed to that of HOMO shapes of 1 and 2 . The present experimental analyses support the theoretical result.

INFRARED SPECTROSCOPY OF TROPOTHIONE

Abstract The IR characterization of tropothione ( 1 ), the sulfur analogue of tropone ( 2 ), is described together with an argument for vibrational assignments for ν(CC) and ν(CO) in 2 . The IR spectrum of 1 is measured in five different solvents as well as in the neat state for assignments. The titled compound 1 exhibits a very strong band of the thiocarbonyl stretching vibration ( ν C  S ) at 1087 cm −1 in CCl 4 . Raman spectrum and ab initio calculated results support the assignment. With the aid of spectroscopy, we have reexamined the assignment of the tropone. The analysis gives rise to the decisive assignment of IR spectroscopies in both 1 and 2 . Two A 1 -symmetry vibrations are coupled in 2 and uncoupled in 1 , respectively.