(9) 30 [Vol. 26,

60. General Considerations on the Substitution Reactions o f .

By Tetsuo NozoE. ChemicalInstitute, Faculty of Science, T~hokuUniversity. (Comm.by R. MAJIMA,M.J.A., Nov. 13, 1950.)

The author'}, some time ago, discovered the presence of an enolic substance, C,OH,2O, in the essential oil of Chamaecyparis taiwanensis, Masamune et Suzuki, and named it hinokitiol. It existed in the oil mainly in a free state and partly as a ferric complex salt, hinokitin, m.p. 252°. From its oxidation and reduc- tion products, especially by the study of crystalline products ob- tained by H202-oxidation, the formula (I), corresponding to C10H1g0~, was adopted. However, as a result of extensive study by the author and his co-workers3~, hinokitiol, m, p. 52°, was found to be isopropylcycloheptatriene-2, 4, 6-ol-2-one-1 (II), corresponding to C,OH,~O2. From its remarkable characteristics, i.e. great stability in spite of its highly unsaturated structure, and the extreme aro- maticity, he assumed4~ its structure to be the resonance hybrid between formulae (ha) and (lib) by the formation of an intra- molecular hydrogen bond. As a result, the links between C-atom

constituting the 7-membered ring, tends to acquire the double-bond character, and the molecule as a whole, takes a plane heptagone structure. This probably, is responsible for the aromaticity of hinokitiol, similar to- that of aromatic compounds of benzene series. The position of the isopropyl group was assumed to be at 4 or meta5~. Erdtman, Gripenberg and Anderson6), entirely independent of the foregoing research, studied the structure of 3 isomeric thuja- plicins, isolated from the heart wood of , Ikon., and gave the same structure (III, R = i-CH) to its $-isomer, m.p. 52°. The coincidence of hinokitiol and , ?- was confirmed by Erdtman by the mixed fusion of the 2 substances. Moreover, Nozoe, et a1.7~, recently proved the structure of hinokitiol by a synthetic method. !o. 9.] General considerations on the Substitution Reactions. (9) 31

Prior to this, Dewars~, had proposed, that this structural frame (III, R = H) was present in the stipitatic acid and colchiceine mole- cules and named this hypothetical mother substance . Since 1948, Jeveral reported the existence of this tropolone nucleus in natural substances, and some related compounds have been synthesiz ed. The synthesis of tropolone itself was also independently carried out recently by Nozoe, et al.;, and by Doering and Knox. As to the exact structure of tropolone and hinokitiol, the author came to the conclusion'°~'2~ that, in order to explain the remarkable characteristics, it is essential to consider a system of resonance between a large number of structures that can be deviled into the following three non-ionic and ionic types (A, B and C). Both hinokitiol and tropolone possess amphoteric character, and, not only are they able to stabilize as an anion (D) in an alkaline medium to give salts or complex salts, but can also stabilize by accepting a proton in the presence of a strong acid to give a conjugate acid cation (E). From this point, they seem to comprise an unique system, which the author wishes to designate as a " tropoloid " system, quite different from that of the benzene series. (9) 32 T. NozoE. [Vol. 26,

In order to examine this unique structure, the author enlisted the help of physical chemists, as well as experimental means of organic chemistry, and made determinations of infrared absorption spectra'2~, dipole moments' ~~and magnetic susceptibility'4~. By Kurita and Kubo'3~ the molecular orbital treatment was also carried out on tropolone, and the ~r-electron distribution, interatomic distances, free valence indices and dipole moments were calculated. It was shown that tropolone and its allied compounds possessed strong tenden- cy to form in tr