Abstract
Novel dialkyloxy- and dihydroxyoctahydroperylenes are regioselectively available via a new tandem Friedel–Crafts alkylation of tetrahydronaphthalene precursors followed by oxidative aromatization. Heating of 5-alkyloxy-1-tetralol with p-toluenesulfonic acid in sulfolane gave the corresponding octahydroperylenes in moderate yields. Studies with Lewis acids and tetralin-1,5-diol in acetonitrile at room temperature provided the 4,10-dihydroxy analogue cleanly, albeit in reduced yields. Examples of these new series of perylene analogues were partially oxidized to the corresponding contiguously aromatic, anthracene core products or fully aromatized to 3,9-dialkyloxyperylenes in good yields.
Perylene and its derivatives2 are important as organic solar cell photoacceptors,3 fluorescent labels for analytical applications, 4 molecular sensors,5 and components for flat-panel displays,6 molecular electronics,7 and solid-state lighting.8 In some photovoltaic materials, perylene photoemission initiates an electron cascade that results in an electric current.9 Commercially Commercially available perylene diimides10 and their derivatives11 are widely employed in these studies.12 Alkyloxy-substituted perylenes13 are attractive targets since they are expected to stabilize perylene radical cation intermediates, resulting in improved photoacceptor properties. Here we describe a regioselective synthesis of 3,9-dialkyloxyperylene (1: Scheme 1) based on a new tandem Friedel–Crafts alkylation of tetrahydronaphthols.
Scheme 1. Tandem Friedel–Crafts Annulation Approach.
Tandem reactions are important processes in organic chemistry because of their pragmatic value and aesthetic appeal.14 Those that involve a Friedel–Crafts reaction in prelude to a second transformation have been reported;15 however, domino Friedel–Crafts reactions are unknown. Recognizing that the perylene skeleton consists of peri-annulated naphthalenes (Scheme 1), we considered a novel route to the perylene core via sequential Friedel–Crafts alkylations. The starting compounds, 5-methoxy- and 5-n-octyloxy-1,2,3,4-tetrahydro-1-naphthols (2a, R = CH3, and 2b, R = n-C8H17, respectively), are accessible from commercially available 5-methoxy-1-tetralone and 1,2,3,4-tetrahydronaphth-1,5-diol (2c, R = H), respectively. Domino Friedel–Crafts alkylations would result in an annulated, partially hydrogenated dialkyloxyperylene skeleton (4; Scheme 2) that can be oxidized to fully aromatic perylene 1. Here we describe results on the implementation of such an approach.
Scheme 2. Products from Tandem Friedel–Crafts Alkylation of Tetrahydronaphthols.
Upon heating in acidic condition (10 mol % TsOH, C6H6, 70 °C, 6 h), 2a (R = Me) generated corresponding olefin 3a initially,16 but under more vigorous conditions (100 mol % TsOH, C6H5Cl, 132 °C, 22 h) a greenish-yellow crystalline precipitate was obtained, which was isolated by filtration (33% mass yield).17 The initial analysis of the solid by 1H and 13C NMR was consistent with a mixture of octahydroperylene 4a (90% of the mixture), a self-condensate of 2a, and a small amount of fluorescent bluish green 5a (<10%; Scheme 2). Mass spectrometry data supported the assignments of both structures. Product 4a was eventually isolated and fully characterized (vida infra).
The isolation of 5-methoxy-1,2,3,4-tetrahydronaphthalene (6a, R = Me) from the filtrate suggested the involvement of 2a or 3a in the oxidation of 4a to 5a. It is likely that the benzylic cation derived under acidic conditions from 2a or 3a abstracts a hydride from 4a to initiate its conversion to 5a (Scheme 3). Thus, this oxidation occurs upon concomitant reduction of 2a (or 3a) to 6a. In accord with this suggestion, oxidation of 4a under hydride abstraction conditions (excess Ph3CCl and lutidine, sulfolane, 120–165 °C, N2) generated a mixture rich in 5a (4a to 5a ratio was shown to be 26:74), which began to precipitate upon cooling below 110 °C.
Scheme 3. Mechanism of Redox Conversions to 5 and 6.
Several experiments were conducted to improve the modest tandem Friedel–Crafts annulation yields (Table 1). As mentioned above, use of 2a with benzene resulted in formation of olefin 3a only, with no evidence of product 4a (entry 1). Reaction in refluxing chlorobenzene gave 4a in modest yield and good selectivity (see entry 2; 9:1 ratio of 4a to 5a), though at higher temperature. Use of nitrobenzene as solvent at 150 °C gave no evidence of product. A similar result was obtained in sulfolane at 132 °C where the starting material and products were destroyed after 22 h of heating giving only a black solution containing traces of 4a and 5a (entry 3). In an identical reaction monitored by TLC 2a gave 4a and 5a in 40% yield and in 1:2 ratio within 2 h (entry 4). Upon employment of the n-octyloxy analogue (2b), prepared via alkylation of the commercially available 1,5-diol (2c), the reaction gave a poor result, as determined by 1H NMR spectroscopy (entry 5). At reduced temperature (95 °C), however, reaction of 2b in sulfolane gave 4b and 5b (ratio of 83:17) in 55% total yield within 26 h (entry 6). In addition, it was observed that at a higher mole percent of catalyst used, the formation of 4b and 5b dominated over 3b (entries 6–8). These reactions were also improved upon use of inert atmosphere, in that less 5b was formed (cf. entry 6 versus entries 9 and 10).
Table 1.
Preparation of Octahydroperylene Derivativesa
| ||||||
|---|---|---|---|---|---|---|
| entry | subst./mol% TsOH | solvent /temp (°C)/time (h) | product(s)b,c
|
isolated yieldd | ||
| 3 | 4 | 5 | ||||
| 1 | 2a/10 | C6H6/70/6 | 99 | 0 | 0 | 90 |
| 2 | 2a/100 | C6H5Cl/132/22 | 0 | 9 | <1 | 33 |
| 3 | 2a/100 | sulfolane/132/12.5 | 0 | tr | tr | 0 |
| 4 | 2a/100 | sulfolane/132/2.0e | -f | -f | -f | 40 (34:66) |
| 5 | 2b/100 | sulfolane/132/12.5 | tr | 5 | 11 | 0 |
| 6 | 2b/100 | sulfolane/95/25 | 9 | 35 | 10 | 55 (83:17) |
| 7 | 2b/50 | sulfolane/95/25 | 12 | 58 | 10 | 55 (83:17) |
| 8 | 2b/20 | sulfolane/95/26 | 4 | 1 | tr | 29 (80:20) |
| 9 | 2b/100 | sulfolane/95/22g | 6 | 53 | 10 | 59 (93:7) |
| 10 | 2b/100 | sulfolane/95/25g,h | -f | -f | -f | 63 (97:3) |
| 11 | 2b/50 | sulfolane/95/25g,h | 6 | 33 | 1 | 58 (97:3) |
| 12 | 2b/100 | sulfolane/95/22g,i | -f | -f | -f | 56 (93:7) |
| 13 | 2c/1.5j | CH3CN/25/24g | -f | -f | -f | 29(<99:1) |
All reactions were performed in 0.5 M (1 mmol scale) in air unless otherwise noted.
Starting material 2a (R = CH3; entries 1–4), 2b (R) = n-C8H17; entries 5–12), or 2c (R = H; entry 13) not detected in TLC (5% EtOAc/hexanes) after indicated reaction time.
Ratio of crude mixture determined by 1H NMR after workup.
Combined yield of the mixture of 4 and 5 (ratio in parentheses).
Reaction performed in 2.0 mmol scale.
NMR ratios not determined.
Reaction performed under N2.
Reaction performed in 3.6 mmol scale.
Reaction performed on 27 mmol scale.
Reaction performed in 0.3 M solution with Hf(OTf)4 as the catalyst.
A sample with a high percentage of 4b (entry 10) was recrystallized in toluene and subjected to single-crystal X-ray diffraction analysis.18 The monomer exhibits antiannulation coupling at the dibenzylic positions (C-6b and C-12b; Scheme 2) and extended octyloxy chains.18a
Oxidation of the mixture of 4a and 5a (entry 2; Table 1) to 3,9-dimethoxyperylene (1a, R = CH3, Scheme 4) occurred upon treatment with 10% Pd/C/cyclododecene.19 The solid product was insoluble in CHCl3 and DMSO but was sparingly soluble in THF. The oxidation product was identified by mass spectrometry (m/z 312) and 1H and 2D COSY NMR spectra, but poor solubility precluded the collection of 13C NMR data. The poor solubility of this compound contrasts sharply with its precursors 4a and 5a, both of which were readily dissolved in CDCl3, and is likely a consequence of strong stacking associations.
Scheme 4. Synthetic Route to Prepare 3,9-Dialkyloxyperylenes.
To afford increased perylene solubility, 4b (R = n-C8H17) was prepared from 2b with use of the TsOH/sulfolane system under N2 (entries 9–12; Table 1). Although the reaction time was as much as 25 h, the optimized reaction condition (3.6 mmol; entry 10) allowed near exclusive formation of 4b (97% of the isolated mixture) in satisfactory yield (63%; entry 10). When the reaction was further scaled up to 27 mmol the products were isolated in the same ratio (93:7) with slightly reduced yield (56%; entry 12) compared to 1 mmol scale (entry 9). As anticipated,17b 3b also formed the product mixture of 4b and 5b (70:30 ratio) in 40% yield under the same conditions. The mixture was subsequently aromatized19 to produce 1b in 90% yield (R = n-C8H17; Scheme 4), which was soluble in a wide range of organic solvents as anticipated. Spectroscopic analysis including NMR, FT-IR, UV, and MS confirmed the formation of novel 4b and its oxidized form 3,9-dioctyloxyperylene (1b).
Tandem Friedel–Crafts reactions of 1,5-diol 2c with TsOH in sulfolane produced intractable mixtures. On the other hand, saturated solutions of 2c in CH3CN (0.3 M) and Lewis acids (0.015 equiv of Sc(OTf)3 or Hf(OTf)4, or 0.30 equiv of La(OTf)3)20 at ambient temperature gave modest yields of diol 4c (19%, 29%, and 27% isolated yields, respectively) along with complex mixtures of unidentified byproducts. The precipitation of 4c from these reaction mixtures allowed its facile isolation without chromatography. Solvent (ether, acetone, THF, EtOAc, CH3NO2) or temperature variation (0–70 °C), or changes in the addition protocol did not improve these results. It is noteworthy that the availability of phenolic 4c (R = H) enables access to diverse perylene analogues.
In summary, domino Friedel–Crafts alkylation/self-condensation of tetrahydronaphthol analogues generated partially hydrogenated dialkyloxyperylene frameworks, which were readily oxidized to anthracenyl and perylenyl products. The selfcondensation can be performed under relatively mild conditions with easily accessible substrates. Additional investigations on the photophysical and photochemical properties of these novel alkyloxyperylenes are ongoing and will be reported in due course.
Experimental Section
5-Methoxy-1,2,3,4-tetrahydro-1-naphthol (2a).21
Prepared from 5-methoxy-1-tetralone as a white solid in 74% yield, mp 69–72 °C (lit.21a mp 74–79). 1H NMR (300 MHz):21b δ 7.19 (t, 1H, J = 8 Hz), 7.06 (d, 1H, J = 8 Hz), 6.76 (d, 1H, J = 8 Hz), 4.82–4.72 (m, 1H), 3.82 (s, 3H), 2.82–2.69 (m, 1H), 2.61–2.47 (m, 1H), 2.01–1.71 (m, 4H), 1.69 (d, 1H, J = 6 Hz). 13C NMR:21b δ 18.0 (t), 22.9 (t), 31.7 (t), 55.3 (q), 68.1 (d), 108.6 (d) 120.5 (d), 126.0 (s), 126.5 (d), 140.0 (s), 157.0 (s). IR (cm−1): 3326, 2935, 1580, 1466, 1427, 1312, 1248, 1042, 1015, 788, 729.
5-(1-Octyloxy)-1,2,3,4-tetrahydro-1-naphthol (2b)
To a flask containing 1,2,3,4-tetrahydronaphthal-1,5-diol (2c; 10.00 g, 61 mmol) in DMF (100 mL) under N2 was added K2CO3 (8.93 g, 65 mmol) and 1-bromooctane (11 mL, 63 mmol). The mixture was heated to 55–60 °C for 4 days while being monitored by TLC (silica gel, 5% ethyl acetate/hexanes). More K2CO3 (1.62 g, 11.7 mmol) and 1-bromooctane (1.4 mL, 8 mmol) were added and heating was continued for another day. The product was extractively isolated and purified by crystallization (hexanes) to give 22.5 g of 2b as a white solid (74% yield), mp 54–56 °C. 1H NMR: δ 7.16 (t, 1H, J = 8.2 Hz), 7.04 (d, 1H, J = 8.2 Hz), 6.73 (d, 1H, J = 8.2 Hz), 4.80–4.73 (m, 1H), 3.98–3.91 (m, 2H), 2.84–2.72 (m, 1H), 2.62–2.48 (m, 1H), 2.03–1.69 (m, 6H), 1.63 (d, 1H, J = 3.9 Hz), 1.54–1.40 (m, 2H), 1.40–1.18 (m, 8H), 0.94–0.82 (m, 3H). 13C NMR: δ 14.1 (q), 18.0 (t), 22.6 (t), 23.0 (t), 26.2 (t), 29.2 (t), 29.3 (t), 31.7 (t), 31.8 (t), 67.8 (t), 69.1 (d), 109.4 (d) 120.2 (d), 126.1 (s), 126.2 (d), 140.0 (s), 156.4 (s). MS (m/z): 276 (M+, 22), 258 (M+ – H2O, 45), 146 (M+ – H2O – C8H16, 100), 145 (M+ – H2O – C8H17, 63). IR (cm−1): 3361, 2919, 2852, 1582, 1459, 1308, 1245, 1077, 1039, 1016, 783, 691. Exact mass analysis calcd for C18H29O2 (MH+) 277.2168, found 277.2165.
General Preparation of Octahydroperylene 4
Aryl ether alcohol 2 (10.0 mmol) and p-toluenesulfonic acid monohydrate (1.95 g, 10.3 mmol) in sulfolane (20 mL) under N2 were heated (at 132 °C for 2a and at 95 °C for 2b) for an appropriate time (2.0 h for 2a and 22 h for 2b) with stirring. The reaction mixture was allowed to cool to room temperature and the resultant precipitate was separated by filtration. The solid was further purified by crystallization (EtOAc/CH2Cl2) to obtain 4 (with a detectable amount of 5) as a greenish yellow solid in both cases.
4,10-Dimethoxy-1,2,3,6b,7,8,9,12b-octahydroperylene (4a)
Prepared from 2a in 37% yield (90:10 ratio of 4a:5a) as a greenish yellow solid, mp 249–252 °C dec. 1H NMR: δ 7.26 (d, 2H, J = 8.3 Hz), 6.84 (d, 2H, J = 8.3 Hz), 3.85 (s, 6H), 3.76–3.70 (m, 2H), 3.10 (ddd, 2H, J = 5.1, 7.1, 16.1 Hz), 2.58–2.47 (m, 4H), 2.05 (ddq, 2H, J = 5.1, 13.2, 8.1 Hz), 1.74 (dddt, 2H, J = 3.9, 7.1, 13.4, 8.5 Hz), 1.51 (tt, 2H, J = 8.5, 12.4 Hz). 13C NMR: δ 20.8 (t), 21.0 (t), 29.8 (t), 36.0 (d), 55.6 (q), 108.6 (d), 124.6 (d), 126.2 (s), 127.9 (s), 136.8 (s), 154.4 (s). MS (m/z): 320 (M+, 95), 319 (M+ – H, 70), 289 (M+ – H – 2CH3 and M+ – OCH3, 100). IR (cm−1): 2929, 2859, 2835, 1602, 1487, 1463, 1346, 1259, 1081, 1002, 800, 753. Calcd for C22H25O2 (MH+) 321.1855, found 321.1853.
4,10-Bis(1-octyloxy)-1,2,3,6b,7,8,9,12b-octahydroperylene (4b)
Prepared from 2b in 60% yield (98:2 ratio of 4b:5b)as a greenish yellow solid, mp 125–127 °C. 1H NMR: δ 7.23 (d, J = 9.0 Hz), 6.81 (d, J = 9.0 Hz), 4.01–3.92 (m, 4H), 3.75–3.69 (m, 2H), 3.16–3.08 (m, 2H), 2.58–2.46 (m, 4H), 2.09–1.99 (m, 2H), 1.84–1.69 (m, 6H), 1.56–1.43 (m, 6H), 1.40–1.24 (m, 16H), 0.92–0.86 (m, 6H). 13C NMR: δ 14.1 (q), 20.9 (t), 21.1 (t), 22.7 (t), 26.2 (t), 29.3 (t), 29.4 (t), 29.5 (t), 29.8 (t), 31.8 (t), 36.0 (d), 68.3 (t), 109.7 (d), 124.5 (d), 126.5 (s), 127.8 (s), 136.8 (s), 153.9 (s). MS (m/z): 516 (M+, 50), 387 (M+ – C8H17O, 100), 275 (M+ – C8H17O – C8H16, 50). IR (cm−1): 2940, 2917, 2848, 1604, 1581, 1465, 1395, 1344, 1261, 1081, 999, 795, 754. Calcd for C36H53O2 (MH+) 517.4046, found 517.4042. Single-crystal X-ray analysis at 223(2) K: triclinic crystal system (space group P1̄) with unit cell dimensions a = 4.608(2) Å, b = 9.424(4) Å, c = 17.933(7) Å, α = 90.869(5)°, β = 95.234(10)°, γ = 103.709(9)°, V = 752.8(6) Å3, Z = 1, and Dx = 1.140 g/cm3.
4,10-Dihydroxy-1,2,3,6b,7,8,9,12b-octahydroperylene (4c)
A mixture of 1,5-dihydroxy-1,2,3,4-tetrahydronaphthalene (2c; 166 mg, 1.01 mmol) and hafnium(IV) trifluoromethanesulfonate (12 mg, 0.015 mmol) in acetonitrile (3 mL) was stirred at room temperature for 30 h. Precipitated solid was separated by centrifugation, washed once with fresh acetonitrile (2 mL), and again with acetonitrile/methanol (1:1; 2 mL) to obtain 4c in 29% yield as a white solid, mp >300 °C dec. 1H NMR (DMSO-d6): δ 8.98 (s, 2H), 7.06 (d, 2H, J = 8.3 Hz), 6.72 (d, 2H, J = 8.8 Hz), 3.60–3.54 (m, 2H), 2.94 (ddd, 2H, J = 4.9, 6.8, 15.6 Hz), 2.47 (ddt, 2H, J = 12.2, 8.3, 4.4 Hz), 2.38 (dt, 2H, J = 15.6, 8.3 Hz), 1.97 (dtt, 2H, J = 4.9, 8.3, 10.2 Hz), 1.63–1.53 (m, 2H), 1.26 (tt, 2H, J = 8.3, 12.2 Hz). 13C NMR (DMSO-d6): δ 20.5 (t), 20.7 (t), 29.7 (t), 35.3 (d), 113.0 (d), 123.4 (s), 124.4 (d), 125.7 (s), 136.3 (s), 151.7 (s). MS (m/z): 292 (M+, 11), 275 (M+ – H2O, 4), 263 (M+ – CH3O, 8), 91 (C7H7+, 100). IR (cm−1): 3261, 2946, 2863, 1591, 1456, 1373, 1299, 1243, 948, 803, 606. Calcd for C20H21O2 (MH+) 293.1536, found 293.1545.
4,10-Dimethoxy-1,2,3,7,8,9-hexahydroperylene (5a)
A mixture of 4a and 5a (40 mg; ~5:1 ratio) was heated with 2,6-lutidine (9 equiv), chlorotriphenylmethane (8 equiv), and p-toluenesulfonic acid (0.66 equiv) in sulfolane at 120–165 °C for 5 h. Upon cooling, a 5a-rich mixture (~74% of 5a) crystallized. The crystals were separated by filtration in 77% yield as a golden solid, mp >260 °C dec. 1H NMR: δ 8.09 (d, J = 9.3 Hz), 7.35 (d, J = 9.6 Hz), 3.98 (s, 6H), 3.50 (t, J = 6.3 Hz), 3.13 (t, J = 6.3 Hz), 2.16 (quintet, J = 6.3 Hz). 13C NMR: δ 22.4 (t), 23.6 (t), 26.9 (t), 56.9 (q), 114.7 (d), 120.7 (s), 122.7 (d), 125.5 (s), 127.2 (s), 128.6 (s), 150.5 (s). MS (m/z): 318 (M+, 100), 303 (M+ – Me, 55). IR (cm−1): 3066, 3008, 2962, 2839, 1581, 1501, 1385, 1248, 1138, 1109, 1038, 823, 762, 684. Calcd for C22H23O2 (MH+) 319.1698, found 319.1695.
3,9-Dimethoxyperylene (1a)
A mixture of 4a and 5a (350 mg, 1.1 mmol), 10% Pd/C (38 mg), and cyclododecene (0.65 mL, 3.5 mmol) in mesitylene (10 mL) was heated at 150–155 °C overnight under N2. Product 1a was isolated as a golden solid after workup (257 mg, 75%), mp >300 °C. 1H NMR (THF-d8): δ 4.02 (s, 6H), 6.94 (d, 2H, J = 8.3 Hz), 7.40 (dd, 2H, J = 7.6, 8.3 Hz), 7.97 (dd, 2H, J = 1.0, 8.3 Hz), 8.16 (dd, 2H, J = 1.0, 7.4 Hz), 8.17 (d, 2H, J = 8.3 Hz). IR (cm−1): 1583, 1503, 1386, 1250, 1040, 825, 805, 764. MS (m/z): 312 (M+, 100), 297 (M+ – Me, 96), 282 (M+ – 2Me, 40). Calcd for C22H16O2 (M+) 312.1150, found 312.1147.
3,9-Bis(1-octyloxy)perylene (1b)
A mixture of 4b and 5b (461 mg, 0.89 mmol), 5% Pd/C (53 mg), and cyclododecene (0.86 mL, 4.46 mmol) in mesitylene (13.5 mL) was refluxed under N2 for 5 h. Product 1b was isolated as a bright yellow solid after workup (410 mg, 90%), mp 219–220 °C. 1H NMR: δ 0.95–0.85 (m, 6H), 1.46–1.21 (m, 16H), 1.64–1.50 (m, 4H), 6.84 (d, 2H, J = 8.6 Hz), 7.44 (t, 2H, J = 7.7 Hz), 8.12–8.01 (m, 6H). Due to its low solubility at room temperature, it was necessary to acquire the 13C NMR spectrum of 1b at 47 °C. Additional peaks beyond the 18 expected were seen, which suggest the formation of isomeric π-stacked dimers. 13C NMR: δ 14.0, 22.7, 26.3, 29.27, 29.38, 29.43, 31.9, 68.4, 77.1, 105.84, 105.87, 119.5 (br), 120.3 (br), 120.6 (br), 124.1, 125.9 (br), 126.0 (br), 126.8, 129.4, 131.6, 154.8. UV (hexanes, nm): 457, 428, 404. IR (cm−1): 3062, 2924, 2582, 1582, 1503, 1467, 1380, 1252. MS (APCI): m/z 508 (M+). Elemental Anal. Calcd for C36H44O2: C, 84.99; H, 8.72. Found: C, 85.12; H, 8.81.
Supplementary Material
Acknowledgments
Preliminary findings were supported by grants from The Welch Foundation (No. 96-086) and the NIGMS (S06 GM08194). R.G. was supported by funds from the NIGMS (MARC-U*STAR GM 07717). We gratefully acknowledge Mr. Justin King, Mr. Ahmed Khan (Minu), and Dr. Fred Lakner for technical contributions.
Footnotes
Supporting Information Available: Proton and 13C NMR spectra of new compounds and crystallographic data for 4b. This material is available free of charge via the Internet at http://pubs.acs.org.
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