J. CHEM. SOC. PERKIN TRANS. I 1985 73 1 Tricyclic I OIAnnulenes. Part 6.' Preparation and Properties of 7b-Ethyl-and 7b- Is0p ro pyI-7bhl-cyclopentcdi nd en es Howard C. Gibbard, Christopher J. Moody, and Charles W. Rees Department of Chemistry, Imperial College of Science and Technology, London SW7 2A Y Previous syntheses of 7b-methyl-7bH-cyclopentcd indene (1a) have been extended to the 7b-ethyl (1b) and 7b-isopropyl (Ic)analogues. All three compounds have similar U.V. and n.m.r. spectra, entirely consistent with their delocalised 1On: aromatic structure. The 7b-ethyl compound undergoes thermal sigmatropic rearrangement to the 2aH-isomer eleven times faster than the 7b-methyl analogue. We have recently described the preparation of 7b-methyl-7bH- cyclopen tcdindene (la), an aromatic tricyclic 1 Olann~lene.~ The aromatic structure, particularly the diamagnetic ring current induced in an applied magnetic field, is supported by its n.m.r.spectrum in which the central methyl group resonates upfield of tetramethylsilane (TMS) at 6 -1.67. With a view to learning more about the aromaticity of these tricyclic lOlannulenes, especially the effect of the induced ring current on the n.m.r. chemical shift of the central substituent, we have now prepared the corresponding 7b-ethyl (lb) and 7b-isopropyl derivatives (lc). Results and Discussion As part of a study on 3-methoxy-3a-substituted-3aH-indenes and their 3-trimethylsiloxy analogues, we prepared the adduct (3) of 3a-ethyl-3-methoxy-3aH-indene (2) and dimethyl acetylenedicarboxylate.The removal of the elements of methanol from the adduct (3) was simply effected by treatment with concentrated sulphuric acid in methanol at 0 "C to give the annulone diester (4) (79). The n.m.r. spectrum of compound (4) confirmed its aromatic structure, and showed, in addition to the expected pattern for the peripheral protons (6 7.59-8.23), an ABX, system in the region upfield of TMS (Figure 1) for the central ethyl group. The methyl group resonated at 6 -0.35, whilst the methylene group appeared as a sixteen-line multiplet centred at 6 -0.98. This multiplet arises from the non-equivalence of the two CH, protons. The diester (4) was converted into the dialdehyde (5) by the method previously described for the 7b-methyl analogue.2 Decarbonylation of the dialdehyde using two equivalents of tris(triphenylphosphine)rhodium(I) chloride in refluxing ben- zene gave the required 7b-ethyl-7bH-cyclopentcdindene (lb) in 77 yield (Scheme 1).The 10Iannulene containing a central isopropyl group was prepared from the tricyclic ketone (6)., Thus reaction of the ketone (6) with 2,4,6-tri-isopropylbenzenesulphonylhydrazide gave a mixture of the hydrazones (7),which was converted into the tetraene (8) by the Shapiro rea~tion.~ Fragmentation of the hydrazones under the basic conditions was rather slow, and this is attributed to the need to form a trianion. The final elimination of water proceeded smoothly to give 7b-isopropyl- 7bH-cyclopentcdindene (Ic) in an overall yield of 28 from the ketone (6)(Scheme 2).The tricyclic lOlannulenes (lb) and (lc) are both bright yellow oils, whose U.V. spectra show a close similarity to that of the methyl-substituted annulene (la) (Table 1). This suggests, not surprisingly, that changing the central alkyl group has very little effect on the electronic structure of the annulene. The aromatic nature of the annulenes (lb) and (lc) was confirmed by their 'H n.m.r. spectra (Figures 2 and 3), the resonances associated with the central alkyl group appearing 6 4/a,3 2 a; R = Me b; R = Et c; R = Pr' Table 1. Electronic spectral data of 7b-substituted-7bH-cyclo-pentcdindenes (1) Compound ~max.(nm) (14 282, 335sh, 450 (1b) 286, 341sh, 451 (Ic) 286, 342sh, 452 Table 2.Chemical shifts of the central groups of 7b-substituted-7bH-cyclopentcdindenes (1) Observed Reference Upfield Compound Protons value (6) value (6) shift (la) CH3 -1.67 0.9 2.57 (lb) CH2CH3 -1.33 1.4 2.73 (Ic) CH(CH3)2 -1.13 1.5 2.63 (lb) CH2CH3 -0.48 0.9 1.38 (Ic) CWCH,), -0.33 0.9 1.23 upfield of TMS as a result of the induced diamagnetic ring current. As studies on tetracyclic 14annulenes, the trans-lOb,lOc-dihydropyrenes, have shown that the ring-current effect is essentially independent of the central substituent,' a similar analysis of the 7bH-cyclopentcdindenes was per-formed by correlating the observed chemical shifts of the central substituents against appropriate reference values (Table 2).Although this rudimentary analysis does not take all factors into account, it does show that the absolute magnitude of the ring current effect, as measured by the upfield shift of the group with respect to the reference value, is approximately independent of the nature of the central substituent. The peripheral protons of the annulenes (lb) and (Ic) resonated in the region 6 7.5-7.95 and appeared as the expected AB and AB, patterns. On heating, the annulene (Ib) rearranged to the laH-isomer (9) by a 1,5 sigmatropic shift of the ethyl group. The driving force for this rearrangement is believed to be the formation of a benzene ring, and relief of the ring-strain at the 2a-position. J. CHEM. SOC.PERKIN TRANS. I 1985 1'1~1~1'1~11111~1~1~1 10 9 8 7 6 5 4 3 2 1 0 -1 6/p. p.m. Figure 1. 250 MHz H N.m.r. spectrum of dimethyl 7b-ethyl-7bH-cyclopentcdindene-1,2-dicarboxylate(4) in deuteriochloroform (region upfield of TMS) (3)1ii @)/ CO,Me CO, Me lv (lb) Scheme 1. Reagents: i, dimethyl acetylenedicarboxylate; ii, conc. H2S04, MeOH, 0 "C; iii, LiAlH,, Et,O; iv, BaMnO,, CH,Cl,, reflux; v, Rh(PPh,),Cl, C6H6, reflux The half-life for this rearrangement was measured by the U.V. method described previously' and found to be 275 min at 109 "C.This contrasts with the corresponding rearrangement of the methyl derivative (t+ 720 min at 138 "C) and gives a relative rate of migration of methyl to ethyl groups of 1 : 11. This is in line with previous work by Dolbier et al.which showed that ethyl has a higher migratory aptitude than methyl in sigmatropic shift^.^ The rearrangement of peripherally substituted tricyclic 10)annulenes was previously found to be faster than the parent annulene (la),' and, in accord with this, the diester (4) rearranged faster (t+ 77 min at 109 "C) than the unsubstituted annulene (lb). This rapid rearrangement of annulenes containing electron-withdrawing groups caused a problem during the preparation of compound (lb) in that the intermediate dialdehyde (5) partially rearranged during the decarbonylation step. Consequently the annulene (lb) was always contaminated with a few percent of the rearranged isomer (9). (8) Scheme 2. Reagents: i, 2,4,6-(Pr'),C,H,SO,NHNH,, Arnberlite IR 120 (H), CHZCl,; ii, MeLi, C,Hamp; iii, 4-MeC6H,SOJH, CH2C12 Experimental For general points see refs.2 and 3. Dimethyl 7b-Ethyl-7bH-cyclopentcdindene-l,2-dicarboxy-late (4).-The adduct (3) (144 mg, 0.46 mmol) was dissolved in methanol (3 ml) and cooled to 0deg;C. Concentrated sulphuric acid (3 ml) was added, and after 15 min the mixture was poured into ice-water (15 ml), and extracted with ether (3 x 15 ml). The combined extracts were dried (MgS04), evaporated, and the residue chromatographed to give the title compound (4) (102 mg, 79) as a bright yellow oil (Found: M+, 284.1045. Cl,H6604requires M+, 284.1049); v,,,. 2 950, 2 920, 1 715, 1 440,l 245,l 220,l 155,l 130, and 820cm-'; h,,,.(EtOH) 311 (log E 4.56) 340 (3.78), and 471 nm (3.30); 6 (250 MHz; CDCI,) -0.98 (2 H, m), -0.35 (3 H, t), 4.00 (3 H, s), 4.04 (3 H, s), 7.59 (1 H, d, J6.7 Hz), 7.65 (1 H, t, J6.7 Hz), 8.01 (1 H, d, J6.7 Hz), 8.13 (1 H, d, J3.8 Hz), and 8.23 (1 H, d, J 3.8 Hz); m/z 284 (M+),253, 252 (base), 238,224, 193,165, and 138.7b-Ethyl-7bH-cyclopent cd indene-1,Zdicarbaldehyde (9.-A solution of the diester (4) (400 mg, 1.41 mmol) in dry ether (25 ml) was added dropwise to a stirred suspension of lithium J. CHEM. SOC. PERKIN TRANS. I 1985 ~ I I I I 2LL I i I I I I 1 I 1 I I I 10 9 8 7 6 5 amp; 3 2 1 0 -1 6/p. p. m. Figure 2. 250 MHz H N.m.r. spectrum of 7b-ethyl-7bH-cyclopent~cdlindene(lb) in deuteriochloroform 8.0 7.5 -0.5 -1.0 6 /p.p . m . Figure 3. 250 MHz H N.m.r. spectrum of 7b-isopropyi-7bH-cyclopentcdindene(lc) in deuteriochloroform (lb) -way to give a dark-red oil. This oil was redissolved in heat dichloromethane (50 ml), treated with barium manganate (3.60 g, 14.0 mmol), and the mixture heated under reflux for 16 h. After cooling, the solution was filtered through Celite, evaporated and chromatographed to give the title compound (5) Et (190 mg, 60) as a red oil, v,,,, 2 940, 1 685, 1 515, 1 430, 1 225, 950, and 830 cm-'; h,,,.(EtOH) 337 (log E 3.98), 363sh (3.24) (9) and 512 nm (3.04); 6 (250 MHz; CDCI,) -0.79 (2 H, q), -0.31 (3 H, t), 7.67 (1 H, d, J7.1 Hz), 7.78 (1 H, t, J 7.1 Hz), 8.29 (1 H, d, J7.1 Hz),8.3(1 H,d,J3.8Hz),8.45(1H,d,J3.8Hz),10.78(1H, aluminium hydride (268 mg, 7.1 mmol) in ether (10 ml) under s), and 10.80 (1 H, s); G,(CDCl,) 7.1, 36.9, 64.5, 118.9, 122.8, nitrogen at room temperature. The resulting mixture was stirred 135.0, 135.6, 137.2, 141.5, 143.6, 162.7, 163.6, 176.8, 187.4, and for 1.5 h at room temperature, and worked up in the standard 188.9;m/z 224 (M'), 195 (base), 167, and 139.734 7b-Ethyl-7bH-cyclopent cdlindene (lb).-A solution of the dialdehyde (5) (112 mg, 0.5 mmol) and tris(tripheny1-phosphine)rhodium(r) chloride (925 mg, 1 mmol) in dry benzene (15 ml) was heated under reflux under nitrogen for 8 h. After cooling, the mixture was treated with iodomethane (2 ml), stirred for a further 1.5 h at room temperature, filtered, and evaporated. The residue was chromatographed to give the title compound(1b) (65 mg, 77) as a bright yellow oil (Found: M', 168.0934.C13HiZ requires M+, 168.0939); v,,,. 3 025, 2 960, 2 925,2 865,2 850,1450,l 370,l 290,l 235,950,925,840,830, 788, 765, 720, 675, 645, and 620 cm-'; h,,,,(EtOH) 286 (log E 4.52), 341sh (3.40), 428sh (2.47), 440sh (2.56), and 451 nm (2.61); 6 (250 MHz; CDCl,) -1.33 (2 H, q), -0.48 (3 H, t), 7.47-7.65 (3 H, AB,, 6,7.50,6-H; 6, 7.62, 5-H and 7-H, JAB 7.5 Hz), and 7.88-7.95 (4 H, AB, 6, 7.90,SB 7.92, JAB 3.3 Hz, 1-H, 2-H, 3-H, and 4-H); S,(CDCl,) 6.5, 34.2, 63.1, 116.3, 129.2, 130.3, 136.0, 159.2, and 178.3; m/z 168 (M+),153 (base), 140, and 139. Closer examination of the n.m.r. spectrum revealed the presence of a small amount of compound (9) as an impurity.Data for compound (9)are given below. Thermal Rearrangement of the Annulene (1b).-A solution of the annulene (lb) (15 mg) in toluene (5 ml) was heated under reflux for 24 h. Evaporation of the solvent, and chromatography of the residue gave 2a-ethyl-2aH-cyclopent cdlindene (9) (1 1 mg, 73) as a pale yellow oil, v,,,. 3 045, 2 960, 2 920, 2 840, 1450, 1 370, 1 325, 930, 835, and 780 cm '; h,,,.(EtOH) 258 (log E 3.91), 284 (3.84) and 346sh nm (2.24); 6 (250 MHz; CDC1,) 0.98 (3 H, t), 1.78 (2 H, q), 6.63 (2 H, d, J 5.0 Hz), 6.75 (2 H, d, J 5.0 Hz), and 6.96-7.17 (3 H, AB,, 7.0 Hz). Thermal Rearrangement of the Annulene Diester (4).-A solution of the annulene diester (4) (40 mg) was heated under reflux in xylene (10 ml) for 3 h.Evaporation of the solvent and chromatography of the residue gave dimethyl 2a-ethyl-2aH- cyclopent cdlindene- 1,2-dicarboxylate (33 mg, 83) as a pale yellow oil, vmaX.2 950,2 925, 1 710, 1 550, 1 455, and 1 430 cm '; h,,,.(EtOH) 253sh, and 314sh nm; 6 (250 MHz; CDC1,) 0.84 (3 H, t), 1.88-2.28 (2 H, qq), 3.85 (3 H, s), 3.94 (3 H, s), 6.67 (1 H, d, J 5.0 Hz), 6.75 (1 H, d, J 5.0 Hz), and 7.08-7.27 (3 H, m). 7b-lsopropyl-7bH-cyclo~entcdlindene (lc).-A mixture of the tricyclic ketone (6) (1 5 mg, 69 pmol), 2,4,6-tri-isopropyl- J. CHEM. SOC. PERKIN TRANS. I 1985 benzenesulphonyl hydrazide (2 1 mg, 70 pmol), and Amberlite resin IR120 (H) (25 mg) was stirred in dichloromethane (10 ml) at room temperature for 2 h. Work-up and chromatography gave (i) the recovered ketone (6) (4.1 mg) and (ii) the hydrazones (7) (21.5 mg, 62). The mixture of the hydrazones (7)(21.5 mg, 43 pmol) was dissolved in benzene and treated with methyl-lithium (1.35~;0.3 ml, 0.47 mmol) at room temperature. The mixture was then warmed to 40deg;C for 1 h, and then quenched with water. The mixture was extracted with ether (3 x 15 ml), and the combined extracts dried and evaporated.The residue was dissolved in dichloromethane (5 ml) and stirred with toluene-4-sulphonic acid (10 mg) for 0.5 h at room temperature. The solvent was evaporated and the residue chromatographed to gve the title compound(1c) (3.6 mg, 28) as a bright yellow oil (Found: M+, 182.1093. C,,H,, requires M+, 182.1095); h,,,.(EtOH) 288, 344sh, 425sh, 439sh, and 452 nm; 6 (250 MHz; CDCl,) -1.13 (1 H, septet), -0.33 (6 H, d), 7.62-7.78 (3 H, AB2, 6, 7.64, 6-H; and 6,7.76,5-H and 7-H; JAB 7.5 Hz), and 7.93 (4 H, AB, 6,7.87, SB7.93,JAB 3.1 Hz, l-H, 2-H, 3-H, and 4-H); m/z 182 (M+)and 139 (base).Acknowledgements We thank the S.E.R.C. for a studentship (H. C. G.). References 1 Part 5, Z. Lidert, R. McCague, C. J. Moody, and C. W. Rees, J. Chem. Soe., Perkin Trans. I, 1984, 383. 2 R. McCague, C. J. Moody, and C. W. Rees, J. Chem. Soc., Perkin Truns 1, 1984, 165. 3 H. C. Gibbard, C. J. Moody, and C. W. Rees, J. Chem. Sue., Perkin Truns. 1, 1985, preceding paper. 4 R. H. Shapiro, Org. React., 1976,23,405. 5 Y. Mao and V. Boekelheide, J. Org. Chem., 1980,452746. 6 I. Fleming and D. H. Williams, 'Spectroscopic Methods in Organic Chemistry,' McGraw-Hill, London, 1980, p. 136. 7 W. R. Dolbier, K. Matsui, L. McCullagh, and K. E. Anapolle, J. Org. Chem., 1979,44,2842. Received 16th July 1984; Paper 4/1221
展开▼
