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Synthesis of furo[b]tropylium tetrafluoroborate
Tetrahedron LettersVol. 21, pp 3375 - 576 OPergamon Press Ltd. 1960. Printed in Great Britain
SYNTHESIS
OF FURO[b]TROPYLIUM
TETRAFLUOROBORATE
Kate*, Bisalco Kobayashi, and Toshio Xiwa Faculty of Science, Osaka City University, Sugimoto-the, Sumiyoshi-ku, Osaka 558, Japan
Masahiko
Summary:
The first synthesis and characterization of the title compound
are described. annelated with heteroaromatic ring have been attracted interest in their stabilities and properties.l-7 we now wish to report the synthesis and characterization of furolbltropylium Tropylium
cations
cation (A), as the stable te~afluoro~rate as follows. Bentaylicbromination of 5,6,7,~-tetr~ydro-4H-cycloheptatblf~~-4~one ($j8 with NBS followed by dehydrobromination with calcium hydrogen phosphate in DMF gave 5,6-dihydro-4H-cyclohepta[bIfuran-4-one ($1 (yield; 72%). The tosylhydrazone, mp. 151-152°C, was treated with methyl lithium in ether' to give 6Hcyclohepta[blfuran ($1 ['78%). The triene $,dissolved in dry ethyl acetate was allowed to react with triphenyfmethyl Eluoborate in acetonitrile to give furo[bltropylium fluoborate (;lj), mp. 194-L95*C (dec.) (34%). The pRR+ value (6.920.3) could be determined by titrating the aqueous solution 13.01 x 10-4 Mol./L)with dilute aq. sodium hydroxide under nitrogen atmosphere.
10
All the 9 signals of C-13 chemical shift were observed; ~(C!D#!N): 115.5, l.37.0,143.8, 145.1, 146.3, 150.5, 150.9r 160.1, 166.1 ppm. The F.i.Cj.1 shows the shifs for compound 3 and 5 ploted against tiheelectron densities calculated by HMO (w-method; ax=1.5, b ~0.7 for oxygen; in the latter case, the electron densities calculated on i?+divinylfuran was used).l' The plots fall on a straight line, except the ones for oxygen-bonded carbons (C2 and CSa) whLch were more deshielded (20-21 ppm) than those expected from the electron densities. The appearance of the C-13 signals fax C4-C9oE compound 5 in a narrow range and at lowez field (~~~~~~{~e~~ - S'$' ~4,~~,~~,~8~mean} = -25.1 ppm) coldpared with the olefinic signals of 412 suggest that the contribution of the struc-
ture 2 to the resonance hybrid &st be important, On the other hand, the deshielding effect of tropy3.iumcation on C-Z (&A#' - 643) = to be larger than that on C-3 (6# - @) = -4.6 ppm). This-:~~~c~~ tlarund there are some minor contribution of structures 1. and 1~ which might act as to increase the PER+ of the tropylium cation,
3375
The PMR spectrum of & showed a complicated feature appeared in the rather field13 [6 (CD3CN):9.70-9.48 (ZB, ml, 9.20-9.05 (4H, mnZ.8.08 ppm (XW, dd, H3)1. The electronic spectrum of ;t in water showed absorptionmaxima, 254 { log E; 4.521, 298 (3.421,and 359 nm (3.711,which gradually changed to new absorptionmaxima, 235 (4.331, 320 run (3.86). The spetrum obtained in 96% sulfuric acid [Amax: 253.5 (log E; 4.681, 295 f3.441, 359 nm 13.7911was similar to the original one in water. lower
a
4
3
2
0
0
5 6
c
a
’
electron density Figure 1. C-13 chemical shifts vs. electron densities for j+ and A_
Refexences f) R. Guilard and P. Fournari, Bull. Sot. Chim. Fr., 1437 (1971):Compt. Rend., 273 (1971). 2) R. Turnbo, D. L, Sullivan, and R. Pettit, J. Am. Chem. SOC.~ E, 5630 (19641. 31 D. N. Nicolaidea and C. IV.Coutrakis, Synthesis, 268 (1977). 4) S. Gronowitz, I3,, Ycm-TOV, and U. Michael, Acta Chem. Stand., 2J 2257 (19731. 587 11978). 51 S. Gronowitz and P. Pedaja, Tetrahedron,& 6) n. El Bolai, It.GulZard, F, Eournari, Y, Dusausoy, and J. Protas, Bull. Sot. Chim, Pr., 75 f1977), 7) K. Komatsu, S. Fmaka, S. Saito, and K. Okamoto, Bull+ Chem- Sec. zpn., 2, 3425 (1977);K. Ok&&o, J. Synth. Org. Chem. Jpn., 3J, 405 (19791. 8) W. v. E. Doering and Lt.R. #nox, J. &n. Chem. SOC.* 2, 3203 (1954). 3) K. A. Eurdett, F. L. Shenton, D. H. YatesI and 3. S. Swenton, Tetrahedron, 30, 2057 (1974). 1 The pH-value at a half n@utraLizationequivalentwas taken as pK +.4 Ill Because iC was difficult to assign each signal to the carrespo&ng carbon in 7-membered ring crf1, we arranged them in the decreasing order to make allot arranged in the same way. to the electron den$itTes for five carbon atoms C -C 12) A. V. Kemp-Jones,A. J‘.Jones, M. Sakai, C: P? B&&an, and S. Masamnne, Can. J. Chem.,-2, 76? (1973). f31
H. Gunther, A, Shyoukh, D. Cremes, and K.-H. Frisch, Ann. Chem., 150 (lO78).
SYNTHESIS
OF FURO[b]TROPYLIUM
TETRAFLUOROBORATE
Kate*, Bisalco Kobayashi, and Toshio Xiwa Faculty of Science, Osaka City University, Sugimoto-the, Sumiyoshi-ku, Osaka 558, Japan
Masahiko
Summary:
The first synthesis and characterization of the title compound
are described. annelated with heteroaromatic ring have been attracted interest in their stabilities and properties.l-7 we now wish to report the synthesis and characterization of furolbltropylium Tropylium
cations
cation (A), as the stable te~afluoro~rate as follows. Bentaylicbromination of 5,6,7,~-tetr~ydro-4H-cycloheptatblf~~-4~one ($j8 with NBS followed by dehydrobromination with calcium hydrogen phosphate in DMF gave 5,6-dihydro-4H-cyclohepta[bIfuran-4-one ($1 (yield; 72%). The tosylhydrazone, mp. 151-152°C, was treated with methyl lithium in ether' to give 6Hcyclohepta[blfuran ($1 ['78%). The triene $,dissolved in dry ethyl acetate was allowed to react with triphenyfmethyl Eluoborate in acetonitrile to give furo[bltropylium fluoborate (;lj), mp. 194-L95*C (dec.) (34%). The pRR+ value (6.920.3) could be determined by titrating the aqueous solution 13.01 x 10-4 Mol./L)with dilute aq. sodium hydroxide under nitrogen atmosphere.
10
All the 9 signals of C-13 chemical shift were observed; ~(C!D#!N): 115.5, l.37.0,143.8, 145.1, 146.3, 150.5, 150.9r 160.1, 166.1 ppm. The F.i.Cj.1 shows the shifs for compound 3 and 5 ploted against tiheelectron densities calculated by HMO (w-method; ax=1.5, b ~0.7 for oxygen; in the latter case, the electron densities calculated on i?+divinylfuran was used).l' The plots fall on a straight line, except the ones for oxygen-bonded carbons (C2 and CSa) whLch were more deshielded (20-21 ppm) than those expected from the electron densities. The appearance of the C-13 signals fax C4-C9oE compound 5 in a narrow range and at lowez field (~~~~~~{~e~~ - S'$' ~4,~~,~~,~8~mean} = -25.1 ppm) coldpared with the olefinic signals of 412 suggest that the contribution of the struc-
ture 2 to the resonance hybrid &st be important, On the other hand, the deshielding effect of tropy3.iumcation on C-Z (&A#' - 643) = to be larger than that on C-3 (6# - @) = -4.6 ppm). This-:~~~c~~ tlarund there are some minor contribution of structures 1. and 1~ which might act as to increase the PER+ of the tropylium cation,
3375
The PMR spectrum of & showed a complicated feature appeared in the rather field13 [6 (CD3CN):9.70-9.48 (ZB, ml, 9.20-9.05 (4H, mnZ.8.08 ppm (XW, dd, H3)1. The electronic spectrum of ;t in water showed absorptionmaxima, 254 { log E; 4.521, 298 (3.421,and 359 nm (3.711,which gradually changed to new absorptionmaxima, 235 (4.331, 320 run (3.86). The spetrum obtained in 96% sulfuric acid [Amax: 253.5 (log E; 4.681, 295 f3.441, 359 nm 13.7911was similar to the original one in water. lower
a
4
3
2
0
0
5 6
c
a
’
electron density Figure 1. C-13 chemical shifts vs. electron densities for j+ and A_
Refexences f) R. Guilard and P. Fournari, Bull. Sot. Chim. Fr., 1437 (1971):Compt. Rend., 273 (1971). 2) R. Turnbo, D. L, Sullivan, and R. Pettit, J. Am. Chem. SOC.~ E, 5630 (19641. 31 D. N. Nicolaidea and C. IV.Coutrakis, Synthesis, 268 (1977). 4) S. Gronowitz, I3,, Ycm-TOV, and U. Michael, Acta Chem. Stand., 2J 2257 (19731. 587 11978). 51 S. Gronowitz and P. Pedaja, Tetrahedron,& 6) n. El Bolai, It.GulZard, F, Eournari, Y, Dusausoy, and J. Protas, Bull. Sot. Chim, Pr., 75 f1977), 7) K. Komatsu, S. Fmaka, S. Saito, and K. Okamoto, Bull+ Chem- Sec. zpn., 2, 3425 (1977);K. Ok&&o, J. Synth. Org. Chem. Jpn., 3J, 405 (19791. 8) W. v. E. Doering and Lt.R. #nox, J. &n. Chem. SOC.* 2, 3203 (1954). 3) K. A. Eurdett, F. L. Shenton, D. H. YatesI and 3. S. Swenton, Tetrahedron, 30, 2057 (1974). 1 The pH-value at a half n@utraLizationequivalentwas taken as pK +.4 Ill Because iC was difficult to assign each signal to the carrespo&ng carbon in 7-membered ring crf1, we arranged them in the decreasing order to make allot arranged in the same way. to the electron den$itTes for five carbon atoms C -C 12) A. V. Kemp-Jones,A. J‘.Jones, M. Sakai, C: P? B&&an, and S. Masamnne, Can. J. Chem.,-2, 76? (1973). f31
H. Gunther, A, Shyoukh, D. Cremes, and K.-H. Frisch, Ann. Chem., 150 (lO78).