(7) 38 [Vol. 26,

42. On the Synthesis of ~Cycloheptatrienolone)'~.

By Tetsuo NozoE, Shuichi SETO,Yoshio KITAHARA, Masao KUNORI,and Yuya NAKAYAMA. ChemicalInstitute, Faculty of Science,. (Comm. by R. MAJIMA,M.J.A., July 12,1950.)

During the recent several years it has been proved that some natural products e. g. hinokitiol2~,stipitatic acid3~,colchicine4~, a-, - , and 7-thujaplicins5~, purpurogallins~ and puberulic acid's etc. -- contain the unsaturated seven-membered cyclic structure (I). Dewar3~assigned the name of "tropolone " to the hitherto unknown cycloheptatrienolone (I) and tried its synthesis, but did not suc- ceeded. Afterward Haworth0>obtained methyltropolone (II) as one of the oxidation products of purpurogallin. Cook9jet al. and recent- ly Tarbell10~et al. reported the syntheses of Benztropolone (III) and its isomer (IV) respectively, The syntheses of tropolone and its alkyl homologues, however, have never been reported.

From the fact that tropolone derivatives are being successively found in nature, their antibiotic properties, the striking action of colchicine to cell division, its curative effect to Sarcoma, and the characteristic prorerties of proved by the studies of Nozoe2~ et al., the problem of synthesizing tropolone has become an attractive one. Hence we tried to synthesize it by various methods. Unlike the case of benztropolone9~, cycloheptanedione (V), on heating with Pd-charcoal, is not dehydrogenated, but resiniied. We, however, succeeded in the synthesis of monocyclic tropolone by dibromination 1) Presented at the 3rd Annual Meeting of the Chemical Society of in Kyoto, April, 2, 1950. 2) Nozoe and Katsura : J. of Pharm. Soc. of Japan, 69, 181 (1944). Nozoe: Science of Drugs (Review in Japanese), 3, 174 (1949). 3) Dewar : Nature, 155, 50 (1945),Corbett et al.: J. C. S. 1950. 197. 4) Dewar : Nature, 155, 141 (1945). 5) Erdtman : ibid., 161, 719 (1948). 6) Barltrop, Nicholson: J. C. S. 1948, 116. 7) Corbett et al.: ibid., 1930, 1, 6. 8) Haworth : ibid., 1948, 1045. 9) Cook: Nature, 163, 410 (1949). 10) Tarbell et al.: J. A. C. S., 72, 379 (1950). No. 7.] On the Synthesis of Tropolone (Cycloheptatrienolone). (7) 39 of (V) with N-bromosuccinimide (N. B. S.) or with bromine, and subsequent dehydrobromination. On dehydrobromination of dibromo-compounds (VI) obtained by the action of 2 moles of N. B. S. to (V), with alcoholic potash sodium acetate, pyridine or dimethylaniline etc., we could scarecely obtain ''tropoloid''. But we found finally that the compounds o " tropoloid series which show red colouration with ferric chloride, were produced on heating (VI) at 90--100° in acidic medium. Tropolone is crystallized in almost colourless prisms melting at 50--51°, after purification through the sparingly soluble sodium salt. This substance is definitely the aimed tropolone, because like hinokitiol it gives various complex salts, moreover it easily gives rise to bromine- and azo-substitution products. On bromination of (V) in glacial acetic acid at 10-15° and subsequent heating at 80-100° the evolution of hydrogen bromide occurred, and a part of the products separated out as sparingly soluble addition product. When decomposed by water, it changed into the crystals melting at 111° and the crystals are proved- monobromotropolone by analysis. From the mother-liquor, we ob- tained mainly this compound, togather with isomeric $-monobromo- tropolone, m. p. 190-191°, and a small quantity of tropolone. We carried out many experiments, changing the quantity of reagents (N. B. S. or bromine), solvents (benzene, ether, chloroform, acetic acid, carbontetrachloride), reaction temperature, catalysts (peroxide, ferric chloride), and the conditions of dehydrobromination. But at present, we have been unable to increase the yields of tropolone and bromotropolone beyond 30 /o and 45 % respectively. On bromination with 3 moles of N. B. S., a small quantity of tropolone, besides mainly a- and $-monobromotropolones, were obtained, while, even when one mole of free bromine in acetic acid, was used, only a small quantity of tropolone was formed and, main products were monobromo derivatives. This fact is noteworthy. Althrough, details of the course of these reactions have not yet been satisactorily cleared, the differences between the use of N~ B. S. and bromine, may be mainly due to the difference of struc tures of dibromo-intermediates (VI), as well as the effect of much more hydrogen bromide formed in the latter case. (7) 40 T. NozoE, S. SETO, Y. KITAHARA, M. KUNORI, and Y. NAKAYAMA. (Vol. 26.

In contrast with the case of the six-membered cyclic mono- ketone11 (VII(, VII=,), in the case of the seven-membered cyclic diketone, the gem-dibromo compound (VI(,) which at first formed, may be unable to " tropolne " accompanying with intramolecular rearrangement, owing to their structural difference. Thus, mono- bromotropolone (VIII) may be mainly formed by such a kind of LiAsproportionation as illustrating below.

When tropolone as well as bromotropolone are treated with excess of bromine, tribromotropolone (IX), melting at 126--127°, is prepared. But the bronlination of tropolone is not always simple, and orange or red coloured "tropoquinonoid " compounds (e. g. X) occur intermediately, then on the decomposition of these compounds, a mixture of several kinds of mono-, di- and tri-bromo substitution products is formed. These details will be reported later.

Azo-compounds of hinokitlol (XI,, R = i-C H7), when heated in alcohol or acetic acid, change easily into the reddish violet sub- stances which may have tropoquinonoid structure (XI,, R = i-C3H7), by rearraEgementl). But azo-compounds of tropolonne (XI« R = H) as well as bromotropolone are very stable and such a rearrangement is scarecely recognized, we suppose therefore, in contrast with the case of tropolone, as soo u as N=N bond of azo-group in azo-der iva- tives of hinokitiol (XI„ R = i-C3H7) is cloven owing to the steric pressure of isopropyl group situated in the adjacent position of azo-group, phenyl-imide group shifts to the neighbouring C atom and thus the azo-compoul~ds of hinokitiol are stabilized in the isomeric tropoquinonoid type (XI,, R = i-C3H7).

11) Djerassi, Scholz: ibid., 69, 2404 (1947). No. 7.] On the Synthesis of Tropolone (Cycloheptatrienolone). (7) 41

Furthermore, it should be noted :that among tropoloize deriva- tives there are considerable difference in their properties -- e. g. in acidity or in stability of inner complex salts -- owing to existence and situation of side chain.

Experimental. Cycloheptanedione ( V). - Cycloheptanone was oxidized by Se02 according to Oodchot's method12~. Yield, 70;0. nv 1.4800--1.4830. Oodchot recorded n; 1.4689. Tropolone (I). - A mixture of dione (V) (9.7 g.), CHC13 (100 C. c.) and N. B. S. (28 g.) was refluxed for 2-3 hours. After the removal of succinimide by filtration and of the solvent by evapora- tion, the residue was heated at 90---100' for 1--2 hours, when hydrogen bromide was evolved, and then distilled in steam. The distillate, contaminated with a small quantity of crystals was fil- tered. The crystals were identical with $-monobromotropolone (de- scribed below), m. p. 190-191° (from ethanol). After concentra- tion of the filtrate which neutralized with NaOH and purification by recrystallization of Na-salt, it was liberated by acid. The crude product, thus obtained, was distilled under reduced pressure and recrystallized from a mixture of benzene and petroleum ether, when it separated in prisms, m. p. 50-51' . Yield, 2.4 g. (Found : C, 68.9; H, 5.2 M. W. 118 (by titration). 071-1602requires C, 68.8; H, 4.9,o M. W. 122) Cu-salt : green needles from CHC13, m. p. 300-303°. Fe-salt : reddish violet needles from CHC13. Ni-salt : brown plates from pyridine. Monobromotropolone (VIII). A solution of bromine (19.2 g.) in acetic acid (15 cc.) was dropwise stirred into a mixture of dione (V) (7.3 g.) and acetic acid (7 cc.) at 12_15c. After the absorption of bromine, the mixture, on heating at 60--80' , evolved violently hydrogen bromide and a large quantity of pale yellow crystals sepa- rated out in 20-30 minutes. The crystals (4.7 g.), m. p. 173-174°, were sparingly soluble in benzene and, on addition of water or alcohol, decomposed into hydrogen bromide and crystals, m. p. 106- 107°. (Sample: 0.765 g. alkali equivalent for (C7H5O2Br+ HBr) is 10.28 cc. of 1/10 N NaOH, found : 10.32 cc.) The crystals, m. p. 106-107 ° , after sublimation and recrystallization from a mixture 12) Godchot: C. r., 202, 326(1936), Haar et al.: J. Org. Chem.,14, 836(1949). (7) 42 T. NOzoE,S. SETO,Y. KITAHARA,M. KUNORI,and Y. NAKAYAMA. [Vol. 2E, of benzene and petroleum ether, separeted in needles, in. p. 111°. (Found : C, 42.2 ; H, 2.4 ?12. W. 199 C7H502Br requires C, 41.8 ; H, 2.4 /o M. W. 201.) Further, a small quantity of crystals (,~-monobromotropolone), m. p. 190--191°, was obtained. (Found : C, 42.8; H, 2.8 n~). Both crystals give reddish violet Fe-comlex salt and yellownish green Cu-salt. From the mother-liquor acetic acid was romoved and then a small quantity of tropolone, m. p. 50°, and dibromo compound, m. p. 157°, accompanying with Q-monobromocompound, m. p. 191°, and a-isomer, m. p. 111°, mentioned above, obtained. Total yield of a--monobromotropolone 3.9 g. Tribromotropolone (IX). This substance was prepared when tropolone as well as monobromotropolone in alcohol were treated with the excess of bromine in the presence of sodium acetate, needles, m, p. 125--126°, from alcohol. (M. W. 355. C7H5O2Br3re- quires M. W. 359) Azo-tropolone (XIa R = R). These substances were prepared by usual azo-coupling to tropolone. Benzene-azo-, reddish orange nee- dles, m. p. 160.5-161.5°; n-bromophenyl-azo-, yellowish brown nee- dles, m. p. 246.5-248°; p-toluyl-azo-, yellowish brown plates, m. p. 202-203.5°; p-methoxy-phenyl-azo--, reddish brown plates, m. p. 186-188°; p-nitrophenyl-azo-, reddish brown microscales m. p. 249-- 250.5°. Azo-bromotropolones. These substances were by usual azo-coupl- ing to a-bromotropolone. p-Tobuyl-azo-, reddish brown needles, n1. p. 184-185'; p-methoxy-phenyl-azo-, brown needles, 173-174°. On performance of this study, the authors thank the members of this laboratory for the zealous co-operation and Dr. Tsuda (Pharmaceutical Institute, University) for microanalyses. Further, for the expense and materials of this research the authors are indebted to the Scientific Reseach Grant of the Department of Education, Takasago Chemical Industry Co., and Kao Soap Co.