2196
Some Chemistry and Crystallography of the Heptafulvenothiophene-Azulenodihydrothiophene System Herman L. Amman,*'" Lanny L. Replogle,lb Plato H. Watts, Jr.,l" Kiyoshi Katsumoto,'b and James M. Stewart1" Contribution from the Department of Chemistry, University of Maryland, College Park, Maryland 20742, and the Department of Chemistry, San Jose State College, San Jose, California 95114. Received M a y 22, 1970 Abstract: The synthesis of 2H-azuleno[l ,8-bc]thiophene and 2-benzoyl-8H-azuleno[1,8-bc]thiophenederivatives has shown that the azulenodihydrothiophene system is thermodynamically more stable than the heptafulvenothiophene tautomer, but that substitution of a strong conjugating group in the 2 position reverses the stability order. The details of several HMO calculations, which lend support to these data, are reported. The crystal and molecular structure of 2-(p-br0mobenzoyl)-5-isopropyl-7-methyl-8H-azuleno[l,8-bc]thiophene has been determined by three-dimensional, X-ray diffraction analysis. The material crystallizes in the monoclinic system with unit cell parameters of a = 9.063, b = 10.807, c = 19.368 A, 0 = 102.38". All of the atoms have been located and refined with full-matrix least squares to a final R index of 0.049. The thiophene ring bond lengths show the influence of conjugation with the benzoyl substituent and these data have been correlated with HMO n-bond orders.
studies2? on Somethe benzenoid tautomer
recent the azulenocyclohexadiene (1)-benzoheptafulvene (2) system have established that 2 is thermodynamically 3/+I
1
\ 3
2
more stable than the azulenoid tautomer 1. These experimental observations are consistent with the relative order of stability suggested by HMO calculations4 of nelectron delocalization energies. Substitution of a sulfur atom for the C(3)-C(4) ethylenic linkage in 2 forms a new heterocyclic molecule which can exist in several tautomeric forms (e.g., 3 and 4) similar to those indicated for 1 and 2. In this case, however, the stability of an azulene 3 us. that of a thiophene 4 must be R?
3
4
a, R, = R, = R, = H
5a, Ar = Ph b, Ar = pBrC,H4
b,Rl =Me; = i-Pr;R3= PhCO c, R, =Me; R, =i-Pr; R3= p-BrC,H,CO (1) (a) University of Maryland; (b) San Jose State College. (2) K. Hafner and H. Schaum, Angew. Chem., Inf. Ed. End., 2, 95 (1 963). (3) V. Boekelheide and C. D. Smith, J. Amer. Chem. Soc., 88, 3950 (1966). (4) (a) There are several possible positions for the tautomeric hydrogen atom in the thiophene derivative, of which structure 4 is one example. In terms of w-HM04b r-electron stability calculations, the delocalization energy of the structure shown below (3.38 p) is slightly larger than that computed for 4a (3.34 p). (b) A. Streitwieser, Jr.,
"Molecular Orbital Theory for Organic Chemists," Wiley, New York, N. Y.,1961, p 135.
Journal of the American Chemical Society / 93:9 / May 5 , 1971
considered, and, in view of the lower resonance energy of thiophene compared to benzene, structure 3 might be expected to be the more stable of the two. Delocalization energies calculated for these two sulfur heterocycles have predicted greater n-electron stability in 3a than 4aO4 However, the recent synthesis of a benzoyldialkyl derivative by treatment of the thiocyano ketone 5a with base, a method which should permit isolation of the most stable isomer, 3b or 4b, has shown that the benzoylheptafulvenothiophene tautomer (4b) predominate~.~ Further data bearing on the question of relative tautomeric stabilities in this heterocyclic system are presented and discussed in this paper.
Experimental Section Melting points were taken on a Fisher-Johns apparatus and are uncorrected. Infrared spectra were recorded using a Beckman IR-5; ultraviolet and visible spectra were taken on a Cary 14. Nuclear magnetic resonance spectra were taken on a Varian A-60 spectrometer except for the dimer 10 which was taken on an HA100, with tetramethylsilane as the internal marker. Coupling constants were taken directly from the spectra and are apparent values. Microanalyses were performed by M-H-W Laboratories, Garden City, Mich., or by Berkeley Analytical Laboratories, Berkeley, Calif. Mass spectra were obtained on Hitachi Perkin-Elmer Model RMU-6E or CEC 21-491 instruments. 7-Isopropyl-l-methyl-4-p-bromophenacylazulene.This ketone was prepared from 1.98 g (10.0 mmol) of guaiazulene, 16.4 ml of a 0.641 N ethereal solution of sodium N-methylanilide (10.5 mmol), and 1.82 g (10.0 mmol) of p-bromobenzonitrile using the methode previously employed for 7-isopropyl-1-methyl-4-phenacylguaiazulene. The product was recrystallized from Skellysolve B giving 2.18 g (58%) of the ketone as blue crystals: mp 132-132.5"; uv Amax (cyclohexane) 254 (log E 4.63), 287 (4.63), 290 (4.62), and (cyclohexane) 610 (log e 2.72), shoulder at 353 nm (3.66); vis A, 631 (2.69), 664 (2.66), and 740 nm (2.33); ir (CCla) 5.95 p (C=O); nmr (CDCI,) 7 2.44 (d, 1, J = 3.5 Hz, H-2), 2.80 (d, 1, J = 3.5 Hz, H-3), 3.07 (d, 1, J = 10 Hz, H-5), 2.57 (dd, 1, J = 10, 1.5 Hz, H-6), 1.77 (d, 1, J = 1.5 Hz, H-8), 2.0-2.6 (m, 4, phenyl), 5.32 (s, 2, CHd, 7.35 (s, 3, 1-Me), 6.93 (m, 1, J = 7 Hz, CH of i-Pr), and 8.67 (d, 6, J = 7 Hz, Me of i-Pr). 7-Isopropyl-l-methyl-3-thiocyano-4-p-bromophenacy~azulene (5b). Thiocyanogen generated from 1.292 g (4.0 mmol) of lead thiocyanate and 20 bromine in carbon tetrachloride solution was allowed to react with 1.524 g (3.88 mmol) of the above ketone ( 5 ) L. L. Replogle, K. Katsumoto, and H. L. Ammon, J. Amer. Chem. Soc., 90, 1086 (1968).
2197 in carbon tetrachloride solution kept at The product was recrystallized from Skellysolve B giving 760 mg (43%;) of 5b as dark (cyclohexane) 261 (log E purple crystals: m p 135-137"; uv ,,A, 4.64), 297 (4.58), shoulder at 351 (3.68), 366 (3.761, and 377 nm (3.86); vis , , A, (cyclohexane) 584 (log e 2.80), and shoulders at 622 (2.75) and 690 nm (2.34); ir (CHC13) 5.91 (C=O) and 4.65 g (S-C-N); nmr (CDCI,) T 2.25 (s, 1, H-2), 2.90 (d, 1, J = 10, Hz, H-5), 2.43 (dd, 1, J = 10, 1.5 Hz, H-6), 1.70 (d, 1, J = 1.5 Hz, H-8), 2.02-2.5 (m, 4, phenyl), 4.73 (s, 2, CH2), 7.42 (s, 3, 1-Me), 6.87 (m, 1, J = 7 Hz, CH of i-Pr), and 8.63 (d, 6, J = 7 Hz, Me of i-Pr). A m / . Calcd for CZ3H2,,BrNOS: C, 63.01; H , 4.60; N, 3.20; S,7.32. Found: C,62.88; H,4.79; N,3.03; S,7.10. 1,4,6-Trimethyl-2H-azuleno[l,8-bc]thiophenium Tetrafluoroborate (7). Hydrogen chloride gas was passed over a cooled (5"), stirred solution of 700 mg (0.043 mmol) of an approximately 2:1 mixture of 6.8-dimethyl-4-methylsulfinylmethylazulene( 6 ) and its isomer 4,8-dimethyl-&metliylsulfinylmethylazulene in 10 ml of acetonitrile until tlc (silica gel, petroleum ether-dichloromethane) indicated maximum Sield of cyclic sulfonium salt (immobile red spot at the origk), The reaction time was cu. 5 min. Solvent and excess hqdrogen chloride were removed it1 I : ~ C I I Oand the residue was dissolved in a small amount of dichloromethane. This solution was extracted with water giving a red aqueous extract and a brown organic phase. An aqueous solution of 0.93 mg (0.48 mmol) of silver tetrafluoroborate was added to the water phase and the resulting precipitate of silver chloride was removed by filtration. The red solution was concentrated by boiling to a small volume, and this was extracted with several large portions of dichloromethane. The combined dichloromethane extracts were dried (NazSOa) and the solvent was removed in t-acuo. Recrystallization of the residue from petroleum ether-dichloromethane gave 28 mg of 7 as red crystals: mp 161.5-164"; uv ,A, (CHC13) 283 (log e 4.49), shoulder at 294 (3.49), 303 (4.59), 332 (3.78), 342 (3.82), and 348 nm (3.86); vis A,,,,, (CHCl,) at 533 (log e 2.92) and shoulder at 640 nm (2.27); nmr (CF3C02H)T 2.15 td, 1 , J = 4 Hz, H-8), ca. 2.4 (m, 3 , H-3, H-5, H-7), 5.55 and 5.98 (pair of doublets, 2, J = 17 Hz, iionequivalent CH, protons), 6.88 (s, 3, 1-Me), 7.02 (s, 3, &Me), and 7.15 (s, 3,4-Me). Aual. Calcd for ClaHljBF&j: C, 55.62; H , 5.01; S, 10.62. Found: C , 55.39; H,4.99; S, 10.36. A second crop of crystals ( 7 mg, mp 158-161') was collected giving a total yield of 25 %. 4,6-Dimethy1-2H-azuleno[l,8-bc]thiophene (8). A mixture of 20 mg of 1,4,6-trimethyl-2H-azuleno[ 1,8-bc]thiophenium tetrafluoroborate (7), 1 ml of pyridine: 500 mg of sodium iodide, and cu. 30 ml of acetone was stirred at'room temperature. After 15 min, tlc (silica gel. petroleum ether) indicated that the reaction was complete, and the mixture was poured into a n ether-water mixture. The blue ether layer was washed with water and dried (NaSO,) and the solvent was removed with a rotary evaporator. Chromatography of the residue on silica gel (Silicar CC-7) using petroleum ether as the eluent gave a single blue band from which the sulfate 8 was isolated as dark blue-green plates in essentially quantitative yield: mp 11 1.5-113.2" (analytical sample had mp (cyclohexane) 238 (log E 4.25), 308 (4.29), 115.5-1 16.5'); u v A,,, 322 (4.38), 369 ( 3 . 4 4 , 387 (3.69). 402 (3.76), and 408 nm (394); vis Anlax (cqclohexane) shoulder at 600 (log t 2.51), 647 (2.64), 692 (2.62), 716 (2.60). 773 (2.30), and 809 nm (2.21); nmr (CDC13) 7 3.08 (s. 2, H-2 and H-3), 3.60 (s, 1. H-5 or H-7), 3.74 (s, 1, H-7 or H-5), 5.16 (s, 2. CH,), 7.54 (s, 3, 4-Me), and 7.67 (s, 3, &Me); mass spectrum (70 eV) mjr (relative intensity) 202 (lo), 201 (12), 200 ( M L ,loo), 199 (34), 186(9), 185 (64), 184(20), 152(10). Anal. Calcd for C13HI2S: C , 77.95; H , 6.04; S, 16.01. Found: C , 77.94; H . 5.99; S, 16.09. There was no change in the visible or near-ultraviolet (300-410 nm) spectrum of 8 when a 3-ml portion of a solution, made from 5.4 mg of the material and 10 ml of methanol, was treated with 10 ~1 of 0.56 N sodium hydroxide. 2-Renzoyl-5-isoprop~l-7-methyl-8H-azuleno[l,8-bc]thiophene (4b). Argon was bubbled through a solution containing 121 mg (0.337 (Sa), mmol) of 7-isopropyl-1 -methyl-4-phenacyl-3-thiocyanoazulene 5 ml of ether, and 8 ml of methanol; then 1.0 ml of 0.55 M methanolic potassium hydroxide in 3 ml of methanol was added over a period of 5 min to the stirred solution. The solution, which had (6) L. L. Replogle, I-C(6)-C(6a)-C(7) moiety shows the single .double bond alternation which is characteristic of acyclic h e ~ a t r i e n e sand ~ ~ of other conjugated a l k e n e ~ 3 These ~ kinds of molecules frequently show double bogd distances as long as the C(6a)--C(7) length of 1.363 A !nd sp2-sp2 single bond lengths as short as the 1.427 A observed for C(6)--C(6a). The mesomeric interaction of the p-bromobenzoyl group with the thiophene ring is reflected by the bond distances in the sulfur heterocycle. Although the thiophene bond length pattern i n 4b cannot be easily rationalized on the grounds of a large contribution of structure l l b to the ground-state resonance hybrid, there is good qualitative agreement with HMO T bond orders. The bond orders computed for both 4b and 2-benzoylthiophene predict that S-C(8a), C(2a)-C(8b), and C(2)*Ph
*Ph 0 lla
+
6Ilb
C( 13) will be shorter, respectively, than S-C(2), C(2)C(2a), and C(13)--C(14), and this trend is found in the observed bond lengths. There is, however, no simple quantitative relationship between the bond orders calculated for 4b and for thiophene, and the bond distances in these molecules. It is interesting to note that the bond orders obtained for the unsubstituted heptafulvenothiophene 4a show very little of the asymmetry found i n the thiophene ring of 4b but that the asymmetry returns on substitution of a formyl group at C(3). The effects of conjugation of the benzene and heptafdvenothiophene moieties with the carbonyl can be seen i n the T bond orders and these interactions may be reflected by t h e C -Oodistance of 1.233 A. Although longer than the 1.215-A average reported3’ for unconjugated aldehydes and ketones, this length is i n line with C -0distances i n aryl ketones.38 In all of the above dis(30) A. Padwa, E. Shefter, aiid E. Alexander, J . Afner. Chem. Soc., 90, 3717 (1968). (31) R . Dcstro, C. M. Gramaccioli, and M. Simonetta, Cheni. Coniniun., 568 (1968). (32) In all of these CRSCS, the substituent para to the bromine has trigonal hybridization. (33) Table 3 in M . Traetteberg, Acta Chem. Sccnid., 22,628 (1968). (34) 15,15’-Dehydrocanthaxantlii1i,J . C. J. Bart aiid C. H . MacGillavry, Acta Crj.stallogr., Sect. B, 24, 1569 (1968); canthaxanthin, J . C. J . Bart and C. H . MacGillavry, ibid., Sect. B, 24, 1587 (1968). (35) The results of several electron diffraction and microwave studies of thiophene”fiarc only in fair accord, but judicious averaging of these d a t a has indicated C--S, C--C, and C-C distances of 1.715, 1.369, aiid 1.428 A,respcctively. (36) B. Bak, D. Christensen, J. Rastrup-Anderson, and E. Tannen, 892 (1956); B. Bak, D. Christensen, L. Hanbaum, J . Clicni. P h ~ , s .25, sen-Sygaard, and J. Rastrup-Anderson, J . Mol. Specfrosc., 7,58 (1961); R . A. Bonham and F. A. Momany, J . Phj,~.Chern., 67, 2474 (1963); W. Hnrshbarger a n d S . H . Bauer, Abstracts, American Crystallographic Association Mecting, Suminer 1968, p 36. (37) L. E. Sutton, Ed., “Tables of Interatomic Distances and Configurations i n Molecules and Ions,’’ Supplement 1956-1959, The Chemical Society, London, England, 1965, p S2ls.
Journal o j the American Chemical Society
1 93:9
May 5, 1971
cussion, cognizance was taken only of the T bond orders and no account was made of effects arising from the u bond network or from the molecular geometry.39 If it is assumed that coplanarity of the carbonyl and thiophene is the most stable arrangement for these groups, then there are two possible conformations about the benzoyl-heptafulvenothiophene bond. One possible arrangement places the benzene opposite to the thiophene while the other has the benzene and sevenmembered ring in close juxtaposition. Molecular models clearly show that the latter conformation is the least stable of the two since it involves substantial nonbonded contacts between the benzene and seven-membered rings. The observed conformation is essentially the first one with a 56” angle between the benzene and thiophene rings, an angle which has probably been forced to relieve the S . . .C(19) and S . ‘H(19) contacts. 40 The conformation places the carbonyl oxygen opposite the seven-membFred ring and produces an H(3). * ‘ 0 distance, 2.36 A, which is smaller than the 2.6-8, sum of the hydrogen and oxygen van der Waals radii. The existence of C - H . . . O hydrogen bonds seems controversial. Hamilton and Ibers4 have classified this kind of interaction as a weak hydrogen boad and they have cited an average 0 . . H distance of 2.3 A, whereas Donqhue4? considers that 0 . . H contacts as short as 2.2 A cannot be interpreted in terms of hydrogen bond formation. In the present case, the hydrogen and oxygen atoms are on opposite sides of the threg-ring plane and deviate from the plane by 0.3 and 0.6 A, respectively. From these data, at least, it would appear that the interaction is repulsive i n nature and hence should not be classed as a hydrogen bond. Acknowledgment. We gratefully acknowledge financial support by the National Science Foundation (GP-3885, GP-7486, and GP-15791) and we thank the Walter Reed Army Hospital (Biochemical Section) for the use of the X-ray diffractometer. The computer time for this project was made available, in part, through the facilities of the Computer Science Center of the University of Maryland. We also wish to thank Dr. Harmon Brown of Varian Associates, Dr. A. H. Struck of Perkin-Elmer Corporation, and D. Raniey of NASAAmes for mass spectral data, and Dr. Leroy Johnson of Varian Associates for an HA-100 nmr spectrum of the dimer. One of us (L. L. R.) gratefully acknowledges a Special Leave for Research from the Trustees of the California State Colleges. e
+
(38) The C-0 distance in benzophenone is 1.23 A and the angle between the benzene rings is 56”: E. B. Fleischer, N. Sung, and S. Hawkinson, J.Phj,s. Chem., 72,4311 (1968). (39) Consideration of the dihedral angles about C(2)-C(13) and C(13)-C(14) was made on defining the resonance integrals for these bonds. (40) The S , ’ , H ( l 9 ) and S . ‘C(19) distances are 2.88 and 3.18 A, respectively. (41) W. C. Hamilton and J. A. Ibers, “Hydrogen Bonding in Solids,” W. A . Benjamin, New York, N. Y., 1968, pp 16and 182. (42) J. Donohue in “Structural Chemistry and Molecular Biology,” A. Rich and N. Davidson, Ed., W. H. Freeman, San Francisco, Calif., 1968, p 443.
