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Novel Diels–Alder adducts formed in the reaction between a few anthracenemethanamines and electron deficient dienophiles
Chemical Data Collections 23 (2019) 100266
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Novel Diels–Alder adducts formed in the reaction between a few anthracenemethanamines and electron deficient dienophiles U. Amrutha, A. Jesna, Jomon P. Jacob∗ Department of Applied Chemistry, Cochin University of Science and Technology, Kochi 682 022, Kerala, India
a r t i c l e
i n f o
a b s t r a c t
Article history: Received 29 January 2019 Revised 11 August 2019 Accepted 13 August 2019 Available online 16 August 2019
Synthesis and characterization of a few novel Diels–Alder adducts are formed by the reaction of a few anthracenemethanamines in xylene with suitable dienophiles viz dimethyl acetylenedicarboxylate and dibenzoylacetylene are discussed herein. In these reactions, we can see the competition between one electron transfer and Diels–Alder reactions. Diels– Alder pathway was the major pathway in all the reactions. All the products formed in the reactions are separated using column chromatography and established the structure mainly using 1 H and 13 C NMR. © 2019 Elsevier B.V. All rights reserved.
Keywords: Anthracenemethanamine Diels-Alder reaction DMAD DBA
Specifications table Subject area Compounds Data category Data acquisition format Data type Procedure Data accessibility
Organic Chemistry, Spectroscopy. Anthracenemethanamines Spectral, Synthesized. 1 H NMR, 13 C NMR, IR, Mass spectra, m.p. Process and analysis. Novel Diels–Alder adducts are synthesized using the reaction between anthracenemethanamines and dienophiles. Data is provided with this article
1. Rationale Anthracenemethanamines are synthesized by Leuckart–Wallach [1,2] and Leuckart reactions [2-9]. Leuckart–Wallach modification with 9-anthraldehyde (1) and N,N-dimethylformamide (2) is used for the synthesis of 1-(anthracen-9yl)-N,N-dimethylmethanamine (3), thereby avoid the usage of gaseous dimethylamine (Scheme 1). Leuckart reaction was carried out using 9-anthraldehyde (1) and 1,2,3,4-tetrahydroquinoline (4) yielded 1-(anthracen-9-ylmethyl)-1,2,3,4tetrahydroquinoline (5). 9-anthraldehyde (1) and N-(anthracen-9-ylmethyl)butan-1-amine (6) undergo Leuckart reaction to give N,N-bis(anthracen-9-ylmethyl)butan-1-amine (7) (Scheme 2). Recently, we have reported the solvent and concentration dependence in the reaction of 9-(N,Ndiisopropylaminomethyl)anthracene with suitable electron-deficient acetylenes such as dimethyl acetylenedicarboxylate (DMAD) (8) and dibenzoylacetylene (DBA) (9) [10,11]. At higher concentration, in nonpolar solvents such as xylene, ∗
Corresponding author at. E-mail address: [email protected] (J.P. Jacob).
https://doi.org/10.1016/j.cdc.2019.100266 2405-8300/© 2019 Elsevier B.V. All rights reserved.
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U. Amrutha, A. Jesna and J.P. Jacob / Chemical Data Collections 23 (2019) 100266
Scheme 1. Synthesis of 1-(anthracen-9-yl)-N,N-dimethylmethanamine (3) by Leuckart–Wallach modification.
Scheme 2. Synthesis of anthracenemethanamines 5/7 by Leuckart reaction.
Fig. 1. Radical cation intermediate of N,N-bis(anthracen-9-ylmethyl)butan-1-amine (7).
9-(N,N-diisopropylaminomethyl)anthracene reacted with DBA and DMAD to give the corresponding Diels–Alder adducts [12,13] as the major product along with 9-anthraldehyde (1), 9-methylanthracene (10) and 9,10-anthraquinone (11) in minor amounts. In the present investigation, we fine-tuned electronic and steric environment around the significant nitrogen atom in anthracenemethanamines and examined their reaction with electron deficient dienophiles in xylene. Each of the selected anthracenemethanamines 3, 5 and 7 possesses its own unique features. In the case of 1-(anthracen-9-yl)-N,Ndimethylmethanamine (3), lowest member of the family having lower steric environment around the nitrogen atom and the lone pair on nitrogen is perfectly localised. 1-(anthracen-9-ylmethyl)-1,2,3,4-tetrahydroquinoline (5) on the other hand suffer from higher steric congestion around nitrogen and lone pair on nitrogen atom is delocalised whereby electron transfer possibility is minimised. Among the three, N,N-bis(anthracen-9-ylmethyl)butan-1-amine (7) has maximum steric crowding around nitrogen. Furthermore, presence of an n–butyl substituent enables Hofmann–Loffler–Freytag reaction-type intramolecular hydrogen abstraction in the incipient radical cation intermediate 7 + (Fig. 1) generated through single electron transfer to 8/9. In the reaction of anthracenemethanamines 3, 5 and 7 with three equivalents of dienophiles 8/9 in refluxing xylene, the corresponding Diels–Alder adducts were formed in moderate yields along with single electron transfer mediated products and intractable polar materials in substantial amounts. In the reaction between 3 and 8, though GC–MS analysis indicated the formation of Diels–Alder adduct 12a in appreciable amounts, our attempts to purify it by different chromatographic separations techniques proved unsuccessful. Adduct 12a is highly polar and it coeluted with other polar materials. However, 12b formed in the reaction between 3 and 9 could be isolated in pure form (Scheme 3).
U. Amrutha, A. Jesna and J.P. Jacob / Chemical Data Collections 23 (2019) 100266
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Scheme 3. Reaction of 1-(anthracen-9-yl)-N,N-dimethylmethanamine (3) with electron deficient acetylenes 8/9.
Scheme 4. Reaction of 1-(anthracen-9-ylmethyl)-1,2,3,4-tetrahydroquinoline (5) with electron deficient acetylenes 8/9.
Scheme 5. Reaction of N,N-bis(anthracen-9-ylmethyl)butan-1-amine (7) with electron deficient acetylenes 8/9.
1-(Anthracen-9-ylmethyl)-1,2,3,4-tetrahydroquinoline (5) reacted efficiently with both 8 and 9 giving the corresponding Diels–Alder adducts 13a,b in very good yields. As expected, delocalisation of the lone pair electrons in 5 made single electron transfer mediated pathways less competitive (Scheme 4). Similarly, 7 also gave Diels–Alder adducts as the major product in its reaction with 8 and 9. Interestingly, we observed that both the anthracene components in 7 undergo Diels Alder reaction to give bisadducts 15a,b in appreciable yields along with mono adduct 14a,b (Scheme 5). In the reaction between 7 and 8/9, products arising through remote hydrogen
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abstractions through a Hofmann-Loffler-Freytag like reaction sequence were not formed in detectable amounts. We attribute this to lower propensity of 7 towards undergoing single electron transfer reaction to give radical cation intermediate 7·+ . In all the reactions between 3/5/7 with 8/9 examined by us, single electron transfer mediated products such as 1, 10 and 11 were formed in small amounts. Dienophiles 8/9 underwent partial oligomerisation to give intractable polar materials that seriously interfered with product separation. 1.1. Conclusions We have explained the reactions of (anthracen-9-yl)methanamines with electron deficient acetylenes in xylene yielded Diels–Alder adduct along with traces of one electron transfer products. Here, we can see the competition between one electron transfer pathway and Diels–Alder pathway. But the major is Diels–Alder pathway. In the above all reactions, we came to know that the electronic and steric environment around the nitrogen atom of (anthracen-9-yl)methanamines has a very little involvement in the product formation. 2. Procedure 2.1. Materials and methods All reactions were carried out using oven dried glasswares. All experiments were performed in distilled and dried solvents by using standard protocols. All starting materials were purchased from either Sigma-Aldrich or Spectrochem Chemicals and were used without further purification. Progress of the reaction and chromatographic separations were monitored by TLC over dried and activated silica gel TLC plates (Aluminium sheets coated with silica gel, E. Merck). Visualisation of TLC plates was acquired by exposure to iodine vapours or UV lamp. Separation and purification of compounds were done by column chromatography using silica gel (Spectrochem Chemicals, 60–120 mesh). The column has 25 cm height, 2.5 cm diameter and the separation was carried out under gravity. The products were further purified by recrystallization from suitable solvent systems. Solvent eluted from the column chromatography was concentrated using Heidolph rotary evaporator. Melting points are uncorrected and were determined on a Neolab melting point apparatus. Infra-red spectra were recorded using Jasco 4100 and ABB Bomem (MB Series) FT-IR spectrometers. The 1 H and 13 C NMR spectra were recorded at 400 MHz Bruker Avance III FT-NMR spectrometer with tetramethylsilane (TMS) as internal standard. Chemical shifts (δ ) are reported in parts per million (ppm) downfield of TMS. Elemental analysis was performed using Elementar Systeme (Vario EL III). GC–MS analysis as was carried out using Agilent GC-7890A, Mass-5975C. Molecular mass was determined by fast atom bombardment (FAB) using JMS 600 JEOL mass spectrometer. Here we are giving the spectral and analytical data only for novel compounds and the corresponding reference cited for known compounds. 2.2. Common procedure for the synthesis of anthracenemethanamines Synthesis of anthracenemethanamines 3, 5 and 7 using Leukart reaction was reported in one of our earlier publications [8]. 2.3. Synthesis of dibenzoylacetylene Dibenzoylacetylene (9) was prepared by a known procedure [10] (75%, mp 109–110 °C). 2.4. Reaction of anthracenemethanamines with dienophiles 2.4.1. Reaction of 1-(anthracen-9-yl)-N,N-dimethylmethanamine (3) with DMAD (8) In a solution (0.16 M) of 3 (0.52 g, 2.2 mmol) in xylene (14 mL), was refluxed with DMAD (1.0 g, 7.0 mmol) for 20 h. Solvent was removed under reduced pressure and the residue was purified by column chromatography on silica gel. Diels– Alder adduct ((9r,10r)-9-((dimethylamino)methyl)-9,10-dihydro-9,10-ethenoanthracene-11,12-diyl)bis(methyl formate) (12a) was formed in considerable amounts, indicated by GC–MS analysis. Adduct 12a is highly polar and was not purified from other polar materials. Along with 12a, trace amounts of 1, 10 and 11 are obtained. 2.4.2. Reaction of 1-(anthracen-9-yl)-N,N-dimethylmethanamine (3) with DBA (9) DBA (1.6 g, 6.8 mmol) was added to a solution of (0.16 M) of 3 (0.52 g, 2.2 mmol) in xylene (14 mL), was refluxed for 20 h. The progress of the reaction was monitored by TLC. After the reaction was complete, the reaction mixture was cooled and the solvent was removed under reduced pressure. The residue obtained was purified by column chromatography on silica gel. The major product formed is the corresponding Diels–Alder adduct 12b (52%). This product is obtained by elution with a mixture (3:2) hexane and ethyl acetate. Along with 12b, trace amounts of 1, 10 and 11 are obtained.
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2.4.3. Reaction of 1-(anthracen-9-ylmethyl)-1,2,3,4-tetrahydroquinoline (5) with DMAD (8) Refluxing a solution (0.16 M) of 3 (0.700 g, 2.2 mmol) in xylene (14 mL) with DMAD (1.0 g, 7.0 mmol) was done for 20 h. The progress of the reaction was monitored by TLC. After the reaction was complete, the reaction mixture was cooled and the solvent was removed under reduced pressure. The residue obtained was purified by column chromatography on silica gel. Elution with hexane gave 1 (traces) and 10 (traces) was obtained by the elution of a mixture of (9:1) hexane and ethyl acetate followed by 11 (2–3%). Major product Diels–Alder adduct 13a (68%) was obtained by the elution using a mixture (7:3) of hexane and ethyl acetate. 2.4.4. Reaction of 1-(anthracen-9-ylmethyl)-1,2,3,4-tetrahydroquinoline (5) with DBA (9) In a solution (0.16 M) of 5 (0.700 g, 2.2 mmol) in xylene (14 mL), was refluxed with DBA (1.6 g, 6.8 mmol) for 20 h.After the complete reaction, the residue obtained by the complete removal of solvent from the reaction mixture was purified by column chromatography on silica gel. Elution with hexane gave 1 (traces) and 10 (traces) was obtained by the elution of a mixture of (9:1) hexane and ethyl acetate followed by 11 (2–3%). Major product Diels–Alder adduct 13b (75%) was obtained by the elution using a mixture (7:3) of hexane and ethyl acetate. 2.4.5. Reaction of N,N-bis(anthracen-9-ylmethyl)butan-1-amine (7) with DMAD (8) DMAD (1.0 g, 7.0 mmol) was added to a solution (0.16 M) of 3 (1.0 g, 2.2 mmol) in xylene (14 mL) and the mixture was refluxed for 20 h. After the reaction was complete, the reaction mixture was cooled and the solvent was removed under reduced pressure. The residue obtained was purified by column chromatography on silica gel. Elution with hexane and a mixture (4:1) of hexane and dichloromethane gave 1 (traces) and 10 (traces) respectively followed by 11 (2%). Further elution with a mixture of (1:1) hexane and dichloromethane gave 14a (23%). Elution using a mixture of (1:4) hexane and dichloromethane gave 15a (33%). 2.4.6. Reaction of N,N-bis(anthracen-9-ylmethyl)butan-1-amine (7) with DBA (9) A solution (0.16 M) of 7 (1.0 g, 2.2 mmol) in xylene (14 mL) was refluxed with DBA (1.6 g, 6.8 mmol) for 20 h. The progress of the reaction was monitored by TLC. After the reaction was complete, the reaction mixture was cooled and the solvent was removed under reduced pressure. The residue obtained was purified by column chromatography on silica gel. Elution with hexane and a mixture (4:1) of hexane and dichloromethane gave 1 (traces) and 10 (traces) respectively followed by 11 (2%). Further elution with a mixture of (1:1) hexane and dichloromethane gave 14b (26%). Elution using a mixture of (2:8) hexane and dichloromethane gave 15b (37%). 3. Data, value and validation 3.1. ((9r,10r)-9-((Dimethylamino)methyl)-9,10-dihydro-9,10-ethenoanthracene-11,12-diyl)bis(phenylmethanone) (12b) Yellow Crystals, Yield 0.27 g (52%); mp: 158–160 °C (EtOAc); IR ν max (KBr): 1652 (C=O stretch), 1593 cm−1 . 1 H NMR (CDCl3 ):- δ 7.45–7.06 (m, 18H), 5.41 (s, 1H), 3.75 (s, 2H), 1.95 (s, 6H). 13 C NMR (CDCl3 ): δ 194.8, 188.8, 155.4, 148.4, 145.7, 138.1, 137.1, 132.7, 131.0, 129.4, 128.0, 127.7, 127.0, 125.1, 124.7, 123.7, 121.6, 60.6, 53.23, 51.1, 44.9. MS-FAB: m/z 469 (M+ ), 105 [C6 H5 CO]+ . Elemental analysis calculated for C33 H27 NO2 (469.58) – C: 84.41, H: 5.80, N: 2.98. Found- C: 84.42, H: 5.79, N: 2.99. 3.2. ((9r,10r)-9-((1,2,3,4-Tetrahydroquinolinyl)methyl)-9,10-dihydro-9,10-ethenoanthracene-11,12-diyl)bis(methyl formate) (13a) Yellow Crystals, Yield 0.48 g (68%); mp: 161–163 °C (MeCN); IR ν max (KBr): 1723, 1703 cm−1 (C=O stretch), 1276 cm−1 (C–O stretch).1 H NMR (CDCl3 ): δ 7.55–6.75 (m, 12H), 5.63 (s, 1H), 4.71 (s, 2H), 3.77 (s, 3H), 3.47 (s, 3H), 3.15 (t, 2H, J = 5.4 Hz), 2.82 (t, 2H, J = 6.4 Hz), 1.86 (quin, 2H, J = 5.6 Hz). 13 C NMR (CDCl3 ): δ 166.6, 164.2, 146.4, 145.3, 145.2, 143.2, 129.6, 127.0, 125.4, 124.9, 124.7, 123.8, 122.3, 117.9, 113.1, 55.1, 52.4, 52.2, 51.1, 49.0, 46.7, 28.0, 21.2. MS-FAB: m/z 465 (M+ ). Elemental analysis calculated for C30 H27 NO4 (465.54) – C: 77.40, H: 5.85, N: 3.00. Found- C: 77.39, H: 5.85, N: 3.01. 3.3. ((9r,10r)-9-((1,2,3,4-Tetrahydroquinolinyl)methyl)-9,10-dihydro-9,10-ethenoanthracene-11,12-diyl)bis(phenylmethanone) (13b) Brown Crystals, Yield 0.53 g (75%); mp: 194–195 °C (EtOAc); IR ν max (KBr): 1655 (C=O stretch), 1598 cm−1 . 1 H NMR (CDCl3 ): δ 7.60–6.50 (m, 22H), 5.45 (s, 1H), 4.54 (s, 2H), 3.04 (t, 2H, J = 5.4 Hz), 2.61 (t, 2H, J = 6.4 Hz), 1.51–1.46 (m, 2H). 13 C NMR (CDCl ): δ 194.7, 192.5, 152.4, 145.9, 145.6, 145.2, 137.4, 136.7, 133.2, 132.3, 129.2, 128.3, 128.0, 126.7, 125.5, 125.1, 3 124.8, 123.8, 122.4, 117.9, 112.5, 56.4, 53.6, 48.9, 46.2, 27.8, 20.6. MS-FAB: m/z 557 (M+ ), 105 [C6 H5 CO]+ . Elemental analysis calculated for C40 H31 NO2 (557.68) – C: 86.15, H: 5.61, N: 2.51. Found- C: 86.14, H: 5.61, N: 2.51. 3.4. ((9r,10r)-9-((N-(anthracen-9-ylmethyl)-N-butan-1-amino)methyl)-9,10-dihydro-9,10-ethenoanthracene-11,12-diyl)bis(methyl formate) (14a) Off White Solid, Yield 0.23 g (23%); mp: 169–171 °C (MeCN); IR ν max (KBr): 1712 (C=O stretch), 1620 cm−1 , 1274 cm−1 (C–O stretch). 1 H NMR (CDCl3 ): δ 8.68–6.82 (m, 17H), 5.42 (s, 1H), 4.85 (s, 2H), 3.88 (s, 2H), 3.64 (s, 3H), 3.13 (s, 3H), 2.76
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(t, 2H, J = 7.8 Hz), 1.92–1.88 (m, 2H), 1.26–1.19 (m, 2H), 0.83 (t, 3H, J = 7.4 Hz). 13 C NMR (CDCl3 ): δ 166.7, 164.3, 153.8, 145.3, 144.9, 143.3, 131.6, 131.6, 130.0, 129.2, 127.8, 125.7, 125.2, 125.0, 124.9, 124.6, 124.4, 123.2, 56.0, 54.8, 52.2, 51.5, 51.1, 51.1, 50.8, 29.6, 21.0, 14.0. MS-FAB: m/z 595 (M+ ), 191 (anthracenemethyl cation). Elemental analysis calculated for C40 H37 NO4 (595.73) – C: 80.65, H: 6.25, N: 2.34. Found- C: 80.64, H: 6.26, N: 2.35. 3.5. ((9r,10r)-9-((N-(anthracen-9-ylmethyl)-N-butan-1-amino)methyl)-9,10-dihydro-9,10-ethenoanthracene-11, 12-diyl)bis(phenylmethanone) (14b) Yellow Crystals, Yield 0.26 g (26%); mp: 174–176 °C (EtOAc). IR ν max (KBr): 1650 (C=O stretch), 1590 cm−1 . 1 H NMR (CDCl3 ): δ 7.90–6.76 (m, 27H), 5.18 (s, 1H), 4.56 (s, 2H), 3.97 (s, 2H), 2.52 (t, 2H, J = 7.8 Hz), 1.45–1.43 (m, 2H), 0.88–0.82 (m, 2H), 0.57 (t, 3H, J = 7.4 Hz). 13 C NMR (CDCl3 ): δ 194.1, 192.6, 152.3, 151.3, 144.8, 144.1, 136.3, 135.9, 131.9, 131.6, 130.6, 130.4, 128.8, 128.1, 127.9, 127.9, 127.1, 126.9, 126.8, 124.6, 124.1, 124.0, 123.8, 123.7, 122.8, 122.2, 54.8, 52.7, 49.5, 49.3, 28.4, 19.7, 12.9. MS-FAB: m/z 687 (M+ ), 191 (anthracenemethyl cation), 105 [C6 H5 CO]+ . Elemental analysis calculated for C50 H41 NO2 (687.87) – C: 87.31, H: 6.01, N: 2.04. Found- C: 87.30, H: 6.01, N: 2.04. 3.6. ((9r,10r)-N,N-bis((9,10-dihydro-9,10-ethenoanthracene-11,12-diyl)bis(methyl formate)-9-methyl))butan-1-amine (15a) Yellow Crystals, Yield 0.33 g (33%); mp: 104–106 °C (MeCN); IR ν max (KBr): 1718 (C=O stretch), 1619 cm−1 , 1262 cm−1 (C–O stretch)., 1 H NMR (CDCl3 ): δ 7.85–6.93 (m, 16H), 5.47 (s, 2H), 4.23 (s, 4H), 3.68 (s, 6H), 3.53 (s, 6H), 2.62 (t, 2H, J = 7.8 Hz), 1.60–1.56 (m, 2H), 1.04–0.98 (m, 2H), 0.64 (t, 3H, J = 7.2 Hz). 13 C NMR (CDCl3 ): δ 167.1, 164.6, 152.9, 145.2, 145.0, 144.2, 125.3, 124.9, 123.9, 123.5, 56.1, 55.9, 52.4, 52.1, 52.0, 51.4, 30.8, 20.6, 13.9. MS-FAB: m/z 737 (M+ ). Elemental analysis calculated for C46 H43 NO8 (737.84) – C: 74.86, H: 5.88, N: 1.90. Found- C: 74.85, H: 5.87, N: 1.91. 3.7. ((9r,10r)-N,N-bis((9,10-dihydro-9,10-ethenoanthracene-11,12-diyl)bis(phenylmethanone)-9-methyl))butan-1-amine (15b) Yellow Crystals, Yield 0.37 g (37%); mp: 139–141 °C (EtOAc); IR ν max (KBr): 1653, 1590 cm−1 (C=O stretch). 1 H NMR (CDCl3 ):- δ 7.47–6.93 (m, 36H), 5.33 (s, 2H), 4.32 (s, 4H), 2.31 (t, 2H, J = 8.0 Hz), 0.88–0.85 (m, 4H), 0.31 (t, 3H, J = 7.2 Hz). 13 C NMR (CDCl ): δ 195.3, 193.9, 152.6, 146.0, 144.9, 137.6, 136.9, 133.0, 132.9, 129.4, 129.0, 128.2, 128.2, 125.1, 124.9, 3 123.3, 123.3, 57.9, 53.8, 53.0, 19.9, 13.6. MS-FAB: m/z 921 (M+ ), 105 [C6 H5 CO]+ . Elemental analysis calculated for C66 H51 NO4 (922.12) – C: 85.95, H: 5.59, N: 1.55. Found- C: 85.96, H: 5.59, N: 1.55. Acknowledgments Financial support for this work was provided by DST (PURSE and FIST schemes), UGC (SAP), and Kerala Government. We thank STIC, Kochi for NMR and elemental analysis. We gratefully acknowledge CUSAT and Kerala Government financial support in the form of Research Fellowships. 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Data Article
Novel Diels–Alder adducts formed in the reaction between a few anthracenemethanamines and electron deficient dienophiles U. Amrutha, A. Jesna, Jomon P. Jacob∗ Department of Applied Chemistry, Cochin University of Science and Technology, Kochi 682 022, Kerala, India
a r t i c l e
i n f o
a b s t r a c t
Article history: Received 29 January 2019 Revised 11 August 2019 Accepted 13 August 2019 Available online 16 August 2019
Synthesis and characterization of a few novel Diels–Alder adducts are formed by the reaction of a few anthracenemethanamines in xylene with suitable dienophiles viz dimethyl acetylenedicarboxylate and dibenzoylacetylene are discussed herein. In these reactions, we can see the competition between one electron transfer and Diels–Alder reactions. Diels– Alder pathway was the major pathway in all the reactions. All the products formed in the reactions are separated using column chromatography and established the structure mainly using 1 H and 13 C NMR. © 2019 Elsevier B.V. All rights reserved.
Keywords: Anthracenemethanamine Diels-Alder reaction DMAD DBA
Specifications table Subject area Compounds Data category Data acquisition format Data type Procedure Data accessibility
Organic Chemistry, Spectroscopy. Anthracenemethanamines Spectral, Synthesized. 1 H NMR, 13 C NMR, IR, Mass spectra, m.p. Process and analysis. Novel Diels–Alder adducts are synthesized using the reaction between anthracenemethanamines and dienophiles. Data is provided with this article
1. Rationale Anthracenemethanamines are synthesized by Leuckart–Wallach [1,2] and Leuckart reactions [2-9]. Leuckart–Wallach modification with 9-anthraldehyde (1) and N,N-dimethylformamide (2) is used for the synthesis of 1-(anthracen-9yl)-N,N-dimethylmethanamine (3), thereby avoid the usage of gaseous dimethylamine (Scheme 1). Leuckart reaction was carried out using 9-anthraldehyde (1) and 1,2,3,4-tetrahydroquinoline (4) yielded 1-(anthracen-9-ylmethyl)-1,2,3,4tetrahydroquinoline (5). 9-anthraldehyde (1) and N-(anthracen-9-ylmethyl)butan-1-amine (6) undergo Leuckart reaction to give N,N-bis(anthracen-9-ylmethyl)butan-1-amine (7) (Scheme 2). Recently, we have reported the solvent and concentration dependence in the reaction of 9-(N,Ndiisopropylaminomethyl)anthracene with suitable electron-deficient acetylenes such as dimethyl acetylenedicarboxylate (DMAD) (8) and dibenzoylacetylene (DBA) (9) [10,11]. At higher concentration, in nonpolar solvents such as xylene, ∗
Corresponding author at. E-mail address: [email protected] (J.P. Jacob).
https://doi.org/10.1016/j.cdc.2019.100266 2405-8300/© 2019 Elsevier B.V. All rights reserved.
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Scheme 1. Synthesis of 1-(anthracen-9-yl)-N,N-dimethylmethanamine (3) by Leuckart–Wallach modification.
Scheme 2. Synthesis of anthracenemethanamines 5/7 by Leuckart reaction.
Fig. 1. Radical cation intermediate of N,N-bis(anthracen-9-ylmethyl)butan-1-amine (7).
9-(N,N-diisopropylaminomethyl)anthracene reacted with DBA and DMAD to give the corresponding Diels–Alder adducts [12,13] as the major product along with 9-anthraldehyde (1), 9-methylanthracene (10) and 9,10-anthraquinone (11) in minor amounts. In the present investigation, we fine-tuned electronic and steric environment around the significant nitrogen atom in anthracenemethanamines and examined their reaction with electron deficient dienophiles in xylene. Each of the selected anthracenemethanamines 3, 5 and 7 possesses its own unique features. In the case of 1-(anthracen-9-yl)-N,Ndimethylmethanamine (3), lowest member of the family having lower steric environment around the nitrogen atom and the lone pair on nitrogen is perfectly localised. 1-(anthracen-9-ylmethyl)-1,2,3,4-tetrahydroquinoline (5) on the other hand suffer from higher steric congestion around nitrogen and lone pair on nitrogen atom is delocalised whereby electron transfer possibility is minimised. Among the three, N,N-bis(anthracen-9-ylmethyl)butan-1-amine (7) has maximum steric crowding around nitrogen. Furthermore, presence of an n–butyl substituent enables Hofmann–Loffler–Freytag reaction-type intramolecular hydrogen abstraction in the incipient radical cation intermediate 7 + (Fig. 1) generated through single electron transfer to 8/9. In the reaction of anthracenemethanamines 3, 5 and 7 with three equivalents of dienophiles 8/9 in refluxing xylene, the corresponding Diels–Alder adducts were formed in moderate yields along with single electron transfer mediated products and intractable polar materials in substantial amounts. In the reaction between 3 and 8, though GC–MS analysis indicated the formation of Diels–Alder adduct 12a in appreciable amounts, our attempts to purify it by different chromatographic separations techniques proved unsuccessful. Adduct 12a is highly polar and it coeluted with other polar materials. However, 12b formed in the reaction between 3 and 9 could be isolated in pure form (Scheme 3).
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Scheme 3. Reaction of 1-(anthracen-9-yl)-N,N-dimethylmethanamine (3) with electron deficient acetylenes 8/9.
Scheme 4. Reaction of 1-(anthracen-9-ylmethyl)-1,2,3,4-tetrahydroquinoline (5) with electron deficient acetylenes 8/9.
Scheme 5. Reaction of N,N-bis(anthracen-9-ylmethyl)butan-1-amine (7) with electron deficient acetylenes 8/9.
1-(Anthracen-9-ylmethyl)-1,2,3,4-tetrahydroquinoline (5) reacted efficiently with both 8 and 9 giving the corresponding Diels–Alder adducts 13a,b in very good yields. As expected, delocalisation of the lone pair electrons in 5 made single electron transfer mediated pathways less competitive (Scheme 4). Similarly, 7 also gave Diels–Alder adducts as the major product in its reaction with 8 and 9. Interestingly, we observed that both the anthracene components in 7 undergo Diels Alder reaction to give bisadducts 15a,b in appreciable yields along with mono adduct 14a,b (Scheme 5). In the reaction between 7 and 8/9, products arising through remote hydrogen
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abstractions through a Hofmann-Loffler-Freytag like reaction sequence were not formed in detectable amounts. We attribute this to lower propensity of 7 towards undergoing single electron transfer reaction to give radical cation intermediate 7·+ . In all the reactions between 3/5/7 with 8/9 examined by us, single electron transfer mediated products such as 1, 10 and 11 were formed in small amounts. Dienophiles 8/9 underwent partial oligomerisation to give intractable polar materials that seriously interfered with product separation. 1.1. Conclusions We have explained the reactions of (anthracen-9-yl)methanamines with electron deficient acetylenes in xylene yielded Diels–Alder adduct along with traces of one electron transfer products. Here, we can see the competition between one electron transfer pathway and Diels–Alder pathway. But the major is Diels–Alder pathway. In the above all reactions, we came to know that the electronic and steric environment around the nitrogen atom of (anthracen-9-yl)methanamines has a very little involvement in the product formation. 2. Procedure 2.1. Materials and methods All reactions were carried out using oven dried glasswares. All experiments were performed in distilled and dried solvents by using standard protocols. All starting materials were purchased from either Sigma-Aldrich or Spectrochem Chemicals and were used without further purification. Progress of the reaction and chromatographic separations were monitored by TLC over dried and activated silica gel TLC plates (Aluminium sheets coated with silica gel, E. Merck). Visualisation of TLC plates was acquired by exposure to iodine vapours or UV lamp. Separation and purification of compounds were done by column chromatography using silica gel (Spectrochem Chemicals, 60–120 mesh). The column has 25 cm height, 2.5 cm diameter and the separation was carried out under gravity. The products were further purified by recrystallization from suitable solvent systems. Solvent eluted from the column chromatography was concentrated using Heidolph rotary evaporator. Melting points are uncorrected and were determined on a Neolab melting point apparatus. Infra-red spectra were recorded using Jasco 4100 and ABB Bomem (MB Series) FT-IR spectrometers. The 1 H and 13 C NMR spectra were recorded at 400 MHz Bruker Avance III FT-NMR spectrometer with tetramethylsilane (TMS) as internal standard. Chemical shifts (δ ) are reported in parts per million (ppm) downfield of TMS. Elemental analysis was performed using Elementar Systeme (Vario EL III). GC–MS analysis as was carried out using Agilent GC-7890A, Mass-5975C. Molecular mass was determined by fast atom bombardment (FAB) using JMS 600 JEOL mass spectrometer. Here we are giving the spectral and analytical data only for novel compounds and the corresponding reference cited for known compounds. 2.2. Common procedure for the synthesis of anthracenemethanamines Synthesis of anthracenemethanamines 3, 5 and 7 using Leukart reaction was reported in one of our earlier publications [8]. 2.3. Synthesis of dibenzoylacetylene Dibenzoylacetylene (9) was prepared by a known procedure [10] (75%, mp 109–110 °C). 2.4. Reaction of anthracenemethanamines with dienophiles 2.4.1. Reaction of 1-(anthracen-9-yl)-N,N-dimethylmethanamine (3) with DMAD (8) In a solution (0.16 M) of 3 (0.52 g, 2.2 mmol) in xylene (14 mL), was refluxed with DMAD (1.0 g, 7.0 mmol) for 20 h. Solvent was removed under reduced pressure and the residue was purified by column chromatography on silica gel. Diels– Alder adduct ((9r,10r)-9-((dimethylamino)methyl)-9,10-dihydro-9,10-ethenoanthracene-11,12-diyl)bis(methyl formate) (12a) was formed in considerable amounts, indicated by GC–MS analysis. Adduct 12a is highly polar and was not purified from other polar materials. Along with 12a, trace amounts of 1, 10 and 11 are obtained. 2.4.2. Reaction of 1-(anthracen-9-yl)-N,N-dimethylmethanamine (3) with DBA (9) DBA (1.6 g, 6.8 mmol) was added to a solution of (0.16 M) of 3 (0.52 g, 2.2 mmol) in xylene (14 mL), was refluxed for 20 h. The progress of the reaction was monitored by TLC. After the reaction was complete, the reaction mixture was cooled and the solvent was removed under reduced pressure. The residue obtained was purified by column chromatography on silica gel. The major product formed is the corresponding Diels–Alder adduct 12b (52%). This product is obtained by elution with a mixture (3:2) hexane and ethyl acetate. Along with 12b, trace amounts of 1, 10 and 11 are obtained.
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2.4.3. Reaction of 1-(anthracen-9-ylmethyl)-1,2,3,4-tetrahydroquinoline (5) with DMAD (8) Refluxing a solution (0.16 M) of 3 (0.700 g, 2.2 mmol) in xylene (14 mL) with DMAD (1.0 g, 7.0 mmol) was done for 20 h. The progress of the reaction was monitored by TLC. After the reaction was complete, the reaction mixture was cooled and the solvent was removed under reduced pressure. The residue obtained was purified by column chromatography on silica gel. Elution with hexane gave 1 (traces) and 10 (traces) was obtained by the elution of a mixture of (9:1) hexane and ethyl acetate followed by 11 (2–3%). Major product Diels–Alder adduct 13a (68%) was obtained by the elution using a mixture (7:3) of hexane and ethyl acetate. 2.4.4. Reaction of 1-(anthracen-9-ylmethyl)-1,2,3,4-tetrahydroquinoline (5) with DBA (9) In a solution (0.16 M) of 5 (0.700 g, 2.2 mmol) in xylene (14 mL), was refluxed with DBA (1.6 g, 6.8 mmol) for 20 h.After the complete reaction, the residue obtained by the complete removal of solvent from the reaction mixture was purified by column chromatography on silica gel. Elution with hexane gave 1 (traces) and 10 (traces) was obtained by the elution of a mixture of (9:1) hexane and ethyl acetate followed by 11 (2–3%). Major product Diels–Alder adduct 13b (75%) was obtained by the elution using a mixture (7:3) of hexane and ethyl acetate. 2.4.5. Reaction of N,N-bis(anthracen-9-ylmethyl)butan-1-amine (7) with DMAD (8) DMAD (1.0 g, 7.0 mmol) was added to a solution (0.16 M) of 3 (1.0 g, 2.2 mmol) in xylene (14 mL) and the mixture was refluxed for 20 h. After the reaction was complete, the reaction mixture was cooled and the solvent was removed under reduced pressure. The residue obtained was purified by column chromatography on silica gel. Elution with hexane and a mixture (4:1) of hexane and dichloromethane gave 1 (traces) and 10 (traces) respectively followed by 11 (2%). Further elution with a mixture of (1:1) hexane and dichloromethane gave 14a (23%). Elution using a mixture of (1:4) hexane and dichloromethane gave 15a (33%). 2.4.6. Reaction of N,N-bis(anthracen-9-ylmethyl)butan-1-amine (7) with DBA (9) A solution (0.16 M) of 7 (1.0 g, 2.2 mmol) in xylene (14 mL) was refluxed with DBA (1.6 g, 6.8 mmol) for 20 h. The progress of the reaction was monitored by TLC. After the reaction was complete, the reaction mixture was cooled and the solvent was removed under reduced pressure. The residue obtained was purified by column chromatography on silica gel. Elution with hexane and a mixture (4:1) of hexane and dichloromethane gave 1 (traces) and 10 (traces) respectively followed by 11 (2%). Further elution with a mixture of (1:1) hexane and dichloromethane gave 14b (26%). Elution using a mixture of (2:8) hexane and dichloromethane gave 15b (37%). 3. Data, value and validation 3.1. ((9r,10r)-9-((Dimethylamino)methyl)-9,10-dihydro-9,10-ethenoanthracene-11,12-diyl)bis(phenylmethanone) (12b) Yellow Crystals, Yield 0.27 g (52%); mp: 158–160 °C (EtOAc); IR ν max (KBr): 1652 (C=O stretch), 1593 cm−1 . 1 H NMR (CDCl3 ):- δ 7.45–7.06 (m, 18H), 5.41 (s, 1H), 3.75 (s, 2H), 1.95 (s, 6H). 13 C NMR (CDCl3 ): δ 194.8, 188.8, 155.4, 148.4, 145.7, 138.1, 137.1, 132.7, 131.0, 129.4, 128.0, 127.7, 127.0, 125.1, 124.7, 123.7, 121.6, 60.6, 53.23, 51.1, 44.9. MS-FAB: m/z 469 (M+ ), 105 [C6 H5 CO]+ . Elemental analysis calculated for C33 H27 NO2 (469.58) – C: 84.41, H: 5.80, N: 2.98. Found- C: 84.42, H: 5.79, N: 2.99. 3.2. ((9r,10r)-9-((1,2,3,4-Tetrahydroquinolinyl)methyl)-9,10-dihydro-9,10-ethenoanthracene-11,12-diyl)bis(methyl formate) (13a) Yellow Crystals, Yield 0.48 g (68%); mp: 161–163 °C (MeCN); IR ν max (KBr): 1723, 1703 cm−1 (C=O stretch), 1276 cm−1 (C–O stretch).1 H NMR (CDCl3 ): δ 7.55–6.75 (m, 12H), 5.63 (s, 1H), 4.71 (s, 2H), 3.77 (s, 3H), 3.47 (s, 3H), 3.15 (t, 2H, J = 5.4 Hz), 2.82 (t, 2H, J = 6.4 Hz), 1.86 (quin, 2H, J = 5.6 Hz). 13 C NMR (CDCl3 ): δ 166.6, 164.2, 146.4, 145.3, 145.2, 143.2, 129.6, 127.0, 125.4, 124.9, 124.7, 123.8, 122.3, 117.9, 113.1, 55.1, 52.4, 52.2, 51.1, 49.0, 46.7, 28.0, 21.2. MS-FAB: m/z 465 (M+ ). Elemental analysis calculated for C30 H27 NO4 (465.54) – C: 77.40, H: 5.85, N: 3.00. Found- C: 77.39, H: 5.85, N: 3.01. 3.3. ((9r,10r)-9-((1,2,3,4-Tetrahydroquinolinyl)methyl)-9,10-dihydro-9,10-ethenoanthracene-11,12-diyl)bis(phenylmethanone) (13b) Brown Crystals, Yield 0.53 g (75%); mp: 194–195 °C (EtOAc); IR ν max (KBr): 1655 (C=O stretch), 1598 cm−1 . 1 H NMR (CDCl3 ): δ 7.60–6.50 (m, 22H), 5.45 (s, 1H), 4.54 (s, 2H), 3.04 (t, 2H, J = 5.4 Hz), 2.61 (t, 2H, J = 6.4 Hz), 1.51–1.46 (m, 2H). 13 C NMR (CDCl ): δ 194.7, 192.5, 152.4, 145.9, 145.6, 145.2, 137.4, 136.7, 133.2, 132.3, 129.2, 128.3, 128.0, 126.7, 125.5, 125.1, 3 124.8, 123.8, 122.4, 117.9, 112.5, 56.4, 53.6, 48.9, 46.2, 27.8, 20.6. MS-FAB: m/z 557 (M+ ), 105 [C6 H5 CO]+ . Elemental analysis calculated for C40 H31 NO2 (557.68) – C: 86.15, H: 5.61, N: 2.51. Found- C: 86.14, H: 5.61, N: 2.51. 3.4. ((9r,10r)-9-((N-(anthracen-9-ylmethyl)-N-butan-1-amino)methyl)-9,10-dihydro-9,10-ethenoanthracene-11,12-diyl)bis(methyl formate) (14a) Off White Solid, Yield 0.23 g (23%); mp: 169–171 °C (MeCN); IR ν max (KBr): 1712 (C=O stretch), 1620 cm−1 , 1274 cm−1 (C–O stretch). 1 H NMR (CDCl3 ): δ 8.68–6.82 (m, 17H), 5.42 (s, 1H), 4.85 (s, 2H), 3.88 (s, 2H), 3.64 (s, 3H), 3.13 (s, 3H), 2.76
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(t, 2H, J = 7.8 Hz), 1.92–1.88 (m, 2H), 1.26–1.19 (m, 2H), 0.83 (t, 3H, J = 7.4 Hz). 13 C NMR (CDCl3 ): δ 166.7, 164.3, 153.8, 145.3, 144.9, 143.3, 131.6, 131.6, 130.0, 129.2, 127.8, 125.7, 125.2, 125.0, 124.9, 124.6, 124.4, 123.2, 56.0, 54.8, 52.2, 51.5, 51.1, 51.1, 50.8, 29.6, 21.0, 14.0. MS-FAB: m/z 595 (M+ ), 191 (anthracenemethyl cation). Elemental analysis calculated for C40 H37 NO4 (595.73) – C: 80.65, H: 6.25, N: 2.34. Found- C: 80.64, H: 6.26, N: 2.35. 3.5. ((9r,10r)-9-((N-(anthracen-9-ylmethyl)-N-butan-1-amino)methyl)-9,10-dihydro-9,10-ethenoanthracene-11, 12-diyl)bis(phenylmethanone) (14b) Yellow Crystals, Yield 0.26 g (26%); mp: 174–176 °C (EtOAc). IR ν max (KBr): 1650 (C=O stretch), 1590 cm−1 . 1 H NMR (CDCl3 ): δ 7.90–6.76 (m, 27H), 5.18 (s, 1H), 4.56 (s, 2H), 3.97 (s, 2H), 2.52 (t, 2H, J = 7.8 Hz), 1.45–1.43 (m, 2H), 0.88–0.82 (m, 2H), 0.57 (t, 3H, J = 7.4 Hz). 13 C NMR (CDCl3 ): δ 194.1, 192.6, 152.3, 151.3, 144.8, 144.1, 136.3, 135.9, 131.9, 131.6, 130.6, 130.4, 128.8, 128.1, 127.9, 127.9, 127.1, 126.9, 126.8, 124.6, 124.1, 124.0, 123.8, 123.7, 122.8, 122.2, 54.8, 52.7, 49.5, 49.3, 28.4, 19.7, 12.9. MS-FAB: m/z 687 (M+ ), 191 (anthracenemethyl cation), 105 [C6 H5 CO]+ . Elemental analysis calculated for C50 H41 NO2 (687.87) – C: 87.31, H: 6.01, N: 2.04. Found- C: 87.30, H: 6.01, N: 2.04. 3.6. ((9r,10r)-N,N-bis((9,10-dihydro-9,10-ethenoanthracene-11,12-diyl)bis(methyl formate)-9-methyl))butan-1-amine (15a) Yellow Crystals, Yield 0.33 g (33%); mp: 104–106 °C (MeCN); IR ν max (KBr): 1718 (C=O stretch), 1619 cm−1 , 1262 cm−1 (C–O stretch)., 1 H NMR (CDCl3 ): δ 7.85–6.93 (m, 16H), 5.47 (s, 2H), 4.23 (s, 4H), 3.68 (s, 6H), 3.53 (s, 6H), 2.62 (t, 2H, J = 7.8 Hz), 1.60–1.56 (m, 2H), 1.04–0.98 (m, 2H), 0.64 (t, 3H, J = 7.2 Hz). 13 C NMR (CDCl3 ): δ 167.1, 164.6, 152.9, 145.2, 145.0, 144.2, 125.3, 124.9, 123.9, 123.5, 56.1, 55.9, 52.4, 52.1, 52.0, 51.4, 30.8, 20.6, 13.9. MS-FAB: m/z 737 (M+ ). Elemental analysis calculated for C46 H43 NO8 (737.84) – C: 74.86, H: 5.88, N: 1.90. Found- C: 74.85, H: 5.87, N: 1.91. 3.7. ((9r,10r)-N,N-bis((9,10-dihydro-9,10-ethenoanthracene-11,12-diyl)bis(phenylmethanone)-9-methyl))butan-1-amine (15b) Yellow Crystals, Yield 0.37 g (37%); mp: 139–141 °C (EtOAc); IR ν max (KBr): 1653, 1590 cm−1 (C=O stretch). 1 H NMR (CDCl3 ):- δ 7.47–6.93 (m, 36H), 5.33 (s, 2H), 4.32 (s, 4H), 2.31 (t, 2H, J = 8.0 Hz), 0.88–0.85 (m, 4H), 0.31 (t, 3H, J = 7.2 Hz). 13 C NMR (CDCl ): δ 195.3, 193.9, 152.6, 146.0, 144.9, 137.6, 136.9, 133.0, 132.9, 129.4, 129.0, 128.2, 128.2, 125.1, 124.9, 3 123.3, 123.3, 57.9, 53.8, 53.0, 19.9, 13.6. MS-FAB: m/z 921 (M+ ), 105 [C6 H5 CO]+ . Elemental analysis calculated for C66 H51 NO4 (922.12) – C: 85.95, H: 5.59, N: 1.55. Found- C: 85.96, H: 5.59, N: 1.55. Acknowledgments Financial support for this work was provided by DST (PURSE and FIST schemes), UGC (SAP), and Kerala Government. We thank STIC, Kochi for NMR and elemental analysis. We gratefully acknowledge CUSAT and Kerala Government financial support in the form of Research Fellowships. 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