1 Department of Chemistry, Shahid Matangini Hazra Govt. College for Women, Nimtouri, West Bengal, India.
2 School of Applied Science and Humanities, Haldia Institute of Technology, Haldia 721657, India.
* E-mail: [email protected] (R. Jana)
¥ All authors want to dedicate this article to Prof. J. K. Ray on his 72nd Birthday (06- January 1950) celebration.
A new approach of reaction mechanism to synthesize 9, 10-dihydro phenanthrene, alkyl phenanthrene, and octa-hydro phenanthrene has been developed via a palladium-catalyzed Heck reaction followed by Reverse Diels-Alder reaction of formaldehyde elimination. The procedure is useful for the synthesis of homologous compounds with a suitable starting material. This will be a new approach to synthesize the phenanthrene derivatives to originate a huge variety of natural and synthetic products for industrial and biomedical applications.
Table of Content
Keywords: Palladium-catalyzed; Heck reaction; Phenanthrene; Revers Diels-Alder reactions; Oxo-palladium complex.
Palladium-catalyzed C-C bond-forming[1-3] reaction is significant for the synthesis of carbocyclic compounds. Polycyclic aromatic hydrocarbons (PAHs), more simply known as polyarenes, constitute extraordinarily large and various classes of organic molecules.[5,6] Phenanthrene is an important core structure of PAH. The phenanthrene moiety can not only be found in several natural products, of which many exhibit interesting biological activity, but more recently phenanthrenes plays an important role as interesting ligands for novel catalyst systems. Previously it was thought that PAHs are direct-acting carcinogens, but it is now accepted that PAHs require metabolic activation to express tumorogenic reactivity.[10,11] Due to its highly lipophilic behavior, phenanthrenes and PAHs are soluble in most organic solvents, and they manifest various functions such as light sensitivity, heat resistance, conductivity; emit ability, corrosion resistance, and physiological action. Numerous synthetic efforts for the preparation of PAHs have been reported by different groups, of which most common is oxidative photocyclization of stilbene derivatives. Among other methods intramolecular Diels–Alder reaction, flash vacuum pyrolysis,[15-18] olefin metathesis, Friedel-Crafts type cyclization, dimerization or trimerization of acetylenes and arynes,[21,22] transition metal-catalyzed cycloisomerization,[23,24] etc. are the key step for making of a benzene ring for the synthesis of PAHs. Palladium-catalyzed C-H bond activation has been used widely in numerous organic syntheses since this reaction gives a solution for the construction of carbo- and heterocycles from the corresponding halides and triflates.[25-31] Some groups have developed a novel Palladium-catalyzed 1,4 migration/C-H activation for the synthesis of complex fused polycycles.[32-34] The major sources of PAHs are crude oil, coal, oil shale. Methylphenanthrene belongs to an important group of alkyl-aromatic hydrocarbons which are present in natural environments. There is a great variety of methods which are available for the synthesis of phenanthrene and its derivatives. Perhaps the most extensive method is the classical Haworth synthesis. The importance of these PAH compounds attracted researchers to synthesize new phenanthrene derivatives and also to try alternate reaction mechanisms. In recent times (2019), Juan et al. has derived a variety of phenanthrene derivatives by palladium-catalyzed controlled Suzuki–Miyaura coupling reaction followed by C–H activation. Scientists also reported efficient approaches for synthesizing functionalized phenanthrenes with a broad substrate range and good functional groups. Recently Jin et.al. reported a series of azole-fused phenanthrenes which are found to be important redox-active organic functional materials. Being inspired by the importance of phenanthrene derivatives and also to find out some new reaction pathways, we have tried a new mechanism to synthesize a series of phenanthrene derivatives which are reported in this article.
Scheme-1 Synthesis of 9,10-dihydro phenanthrene compounds by palladium-catalyzed 6 electrocyclic reaction.
2. Result and discussion
From our laboratory, we first reported a novel and rapid synthesis of substituted 9, 10-dihydrophenanthrene compounds by a palladium-catalyzed 6 electrocyclic reaction. (Scheme 1).
When 1 was treated with Pd(OAc)2 (10 mol%), Cs2CO3 (2 Eqv.), PPh3 (0.5 Eqv.), TBAC (1 Eqv.), in DMF solvent, heated at 85 oC -90 oC for 1.5 h – 2 h, the unexpected products 2 was obtained in good yield. A fused aromatic ring resulted from cleavage of the pyran ring present in the substrate followed by ring closer and aromatization. We examined the scope of the reaction with different substituted 2-(1-bromo-3,4-dihydro-naphthene-2-yl)-3,6-dihydro-2H-pyran, 2-(2-bromo-3,4-dihydro-naphthene-1-yl)-3,6-dihydro-2H-pyran, 4–bromo-3-(3,6-dihydro-2H-pyran-2-yl)-2H-chromene and 2-(2-bromo-acenaphthylen-yl)-3,6-dihydro-2H-pyran (1a-i) as shown in (Table 1) with satisfactory yields were obtained in this reaction. This reaction represents a unique method for the preparation of 9,10-dihydrophenanethrene and its analogs from vinyl bromoaldehydes.
Table1. Reactents and products of scheme-1.
Reagent and condition: 1 (a-i) (1 equiv), Pd(OAc)2 (10 mol %), PPh3 (0.5 equiv), Cs2CO3 (2 equiv), n-Bu4NCl (1 equiv) DMF (6-7 mL), heated at 85-90 oC.
By using this methodology, we have synthesized Fluoranthene in the following way:
Scheme-2. Synthesis of fluoranthene from vinyl bromoaldehydes.
Initially, we thought that the reaction mechanism (Scheme 3) occurs through a 6 electrocyclic ring closer reaction followed by formaldehyde elimination. Our proposed catalytic cycle involves initial oxidation of the Pd(0) to palladium (II) intermediate (A) via oxidative addition of the Pd(0) to the substrate, which then co-ordinates with oxygen to generate the intermediate (B).
Scheme-3. 6 electrocyclic ring closer reaction mechanism.
Then the proton abstraction is followed by rearrangement to generate cyclic O-Pd complex (C). Then the 6π electrocyclic ring closer disrotation reaction forming complex (D), followed by formaldehyde elimination to afford 9,10-dihydrophenanthrene. Lan et al. proposed an alternative mechanism of our reaction that occurs through an intramolecular Heck reaction. Using theoretical calculations they investigated both the mechanisms and find that the intramolecular Heck mechanism (Scheme 4) is lower in energy than the electrocyclic pathway (Scheme 3).
Scheme-4. Intramolecular Heck reaction mechanism proposed by Lan et al.
We have prepared 9,10-dihydrophenanthrenes by palladium-catalyzed reaction first from vinyl bromoaldehydes. Then we have utilized our methodology for the aromatic bromoaldehydes system, and we got a successful result to synthesize phenanthrene and alkyl phenanthrene in moderate to good yield. The significance of this method is that we can introduce one or two alkyl groups at newly formed benzene ring (c) of phenanthrene (Scheme 5).
Scheme-5. Synthesize phenanthrene and alkyl phenanthrene from aromatic bromoaldehydes.
Scheme-6. Reaction pathway for the synthesis of phenanthrene and 2-methoxy phenanthrene from aromatic bromoaldehydes.
Scheme-7. Reaction pathway for the synthesis of alkyl phenanthrene from aromatic bromoaldehydes.
First homo allyl alcohols 8a and 8b were obtained from aromatic bromoaldehydes 7a, 7b by the reaction with allyl bromide, sodium iodide in presence of indium metal. These alcohols were converted to diallylated compounds 9a and 9b in presence of sodium hydride and allyl bromide in THF medium at 0 oC temperature which was subjected to ring-closing metathesis (RCM) reaction by Grubbs catalyst to obtain desired cyclic precursor 10a and 10b respectively. These cyclic precursors were finally treated with Pd(OAc)2 , PPh3, Cs2CO3 in DMF solvent at 85-90 oC to obtain phenanthrene 11a and 2-methoxy phenanthrene 11b in good yield which is shown in Scheme 6.
To introduce alkyl groups, homo allyl alcohols (8b and 8c) were obtained first from aromatic bromoaldehydes 7b and 7c by the reaction with allyl bromide, sodium iodide in presence of indium metal. These alcohols were converted to diallylated
Scheme-8. Reaction pathway for the synthesis of alkyl phenanthrene from aromatic bromoaldehydes.
Scheme-9. Reaction pathway for the synthesis of dialkyl phenanthrene from aromatic bromoaldehydes.
compounds 9c and 9d in presence of sodium hydride and allyl bromide in THF medium at 0 oC temp., which were subjected to metathesis reaction by Grubbs catalyst to obtained desired cyclic precursor 10c and 10d respectively. These cyclic precursors were finally treated with Pd(OAc)2 , PPh3, Cs2CO3 in DMF solvent at 85-90 oC to obtained alkyl phenanthrenes 11c, 11d respectively in good yield which is shown in (Scheme 7).
To alternating the position of methyl group, the same aromatic bromoaldehydes 7b and 7c were treated with methyallylbromide, sodium iodide in presence of indium metal to obtained compounds 8d, 8e. These alcohols were then converted to diallylated compounds 9e, 9f in presence of sodium hydride and allyl bromide in THF medium at 0 oC which were contingent upon Grubbs catalyzed metathesis reaction to obtain desired cyclic precursor 10e, 10f respectively. These cyclic precursors were finally treated with Pd(OAc)2, PPh3, Cs2CO3 in DMF solvent at 85-90 oC to obtained alkyl phenanthrenes 11e, 11f respectively in good yield which is shown in (Scheme 8).
Scheme-10. Synthesis of 1,2,3,4,4a,9,10,10a-octahydro-phenanthrene.
We can introduce two alkyl groups in phenanthrene ring at the same time. First homo allyl alcohols 8d and 8e were obtained from aromatic bromoaldehydes 7a, 7c by the reaction with allyl bromide, sodium iodide in presence of indium metal. These alcohols were converted to diallylated compound 9g and 9h in presence of sodium hydride and allyl bromide in THF medium at 0 oC which were subjected to metathesis reaction by Grubbs catalyst to Obtained desired cyclic precursor 10 g and 10h respectively. These cyclic precursor were finally treated with Pd(OAc)2, PPh3, Cs2CO3 in DMF solvent at 85-90 oC to obtained dialkyl phenanthrenes 11g and 11h in good yield which is shown in (Scheme 9).
By using above methodology, we can synthesized 1,2,3,4,4a,9,10,10a-octahydro-phenanthrene (Scheme 10) which is a core structure of various natural product like totarol, cis-4a-methyloctahydrophenanthrene, podocarpa-8,11,13-triene.
In this article, we have reported a series of different phenanthrene derivatives like 9, 10-dihydrophenanthrene, phenanthrene, mono- and di-alkylated phenanthrene, and octahydrophenanthrene derivatives with this new reaction pathway. This method also useful for the synthesis of higher homologous polynuclear aromatic hydrocarbons provided an efficient route to the synthesis of suitable starting material. This will be a new approach to synthesize the phenanthrene derivatives to originate a wide variety of natural and synthetic products with industrial and biomedical applications.
The general procedures for the synthesis of compounds are reported in supporting information file (Text S1) along with all spectral graphs (Figure S1). Some selected analytical data are reported here for the reference of synthesized compounds.
4.1 Some selected data:
4.1.1 1-(2-Bromo-naphthalen-1-yl)-3-methyl-but-3-en-1-ol (8e)
Liquid, 1H NMR (CDCl3, 400 MHz) : 1.93 (s, 3H), 2.52 (m, 2H), 2.93 (m, 1H), 4.96 (s, 1H), 4.99 (s, 1H), 5.90 (dd, 1H, J = 3.6Hz, J = 10.4Hz), 7.41-7.56 (m, 2H), 7.58 (s, 2H), 7.80 (dd, 1H, J = 6.4Hz, J = 8Hz), 8.83 (d, 1H, J = 8Hz). 13C NMR (CDCl3, 100 MHz) : 22.29, 44.75, 73.35, 114.027, 121.11, 125.90(2C), 126.16, 128.70, 129.48, 130.16, 132.25, 133.67, 136.81, 142.38. Anal. Calcd for C15H15BrO: C, 61.87; H, 5.19 Found: C, 61.95; H, 5.13.
4.1.2 1-(1-Bromo-7-methoxy-naphthalen-2-yl)-but-3-en-1-ol (8b)
Liquid, 1H NMR (CDCl3, 200 MHz) : 1.89 (s, 3H), 1.98 (brs), 2.23-2.33 (m,1H), 2.56-2.62 (m, 1H), 3.93 (s, 3H), 4.92 (m, 2H), 5.42 (d, 1H, J = 3Hz), 5.47 (d, 1H, J = 3Hz), 7.10 (d, 1H, J = 2.4Hz), 7.17-7.23 (m, 1H), 7.66 (m, 2H), 8.20 (d, 1H, J = 9Hz). 13C NMR (CDCl3, 100 MHz): 21.10, 47.73, 55.42, 72.89, 107.05, 115.20, 119.91, 121.5, 124.72, 127.91, 127, 128.90, 136.27, 138.51, 143.57, 159.07. Anal. Calcd for C16H17BrO2: C, 59.83; H, 5.33 Found: C, 59.95; H, 5.21.
4.1.3 1-Bromo-2-[1-(2-methyl-allyloxy)-but-3-enyl]-naphthalene (9c)
Liquid, 1H NMR (CDCl3, 200 MHz) δ: 1.83(s, 3H), 2.57 (t, 2H, J = 6.4Hz), 3.73(d, 1H, J = 12.6Hz), 3.84 (d, 1H, J = 12.6Hz), 4.91-5.18 (m, 5H), 5.85-6.02 (m, 1H), 7.49-7.65 (m, 3H), 7.84 (d, 2H, J = 8Hz), 8.34 (d, 1H, J = 8Hz). 13C NMR (CDCl3, 50 MHz) δ: 19.76, 41.23, 72.89, 79.98, 112.44, 117.18, 123.02, 124.81, 126.54, 127.47, 128.09, 128.17, 132.19, 134.20, 134.61, 139.40, 142.09.
4.1.4 1-Bromo-2-[3-methyl-1-(2-methyl-allyloxy)-but-3-enyl]-naphthalene (9g)
Liquid , 1H NMR (CDCl3, 200 MHz) : 1.75 (s, 3H), 1.90 (s, 3H), 2.49 (m, 2H), 3.68 (d, 1H, J = 12.4Hz), 3.83 (d, 1H, J = 12.4Hz), 4.83-4.99 (m, 4H), 5.25 (dd, 1H, J = 5.4Hz, J = 7.6Hz), 7.49-7.68 (m, 3H), 7.84 (dd, 2H, J = 2.4Hz, J = 8.6Hz), 8.36 (dd, 1H, J = 8.2Hz, J = 0.8Hz). 13C NMR (CDCl3, 100 MHz) : 19.88, 23.07, 45.41, 73.22, 79.57, 112.50, 113.21, 123.07, 124.93, 126.66, 127.55(2C), 128.32(2C), 132.41, 134.39, 140.14, 142.36, 142.58. Anal. Calcd for C19H21BrO: C, 66.09; H, 6.13 Found: C, 59.95; H, 6.25.
4.1.5 2-(1-bromo-naphthalen-2-yl)-5-methyl-3,6-dihydro-2H-pyran (10c)
Liquid, 1H NMR (CDCl3, 200 MHz) δ: 1.70 (s, 3H), 2.04-2.22 (m, 1H), 2.42-2.55 (m, 1H), 4.19-4.40 (m, 2H), 5.15 (dd, 1H, J = 3.4Hz, J=10.4Hz), 5.64 (m, 1H), 7.46-7.63 (m, 2H), 7.71 (m,1H), 7.79-7.87 (m,2H), 8.32 (d, 1H, J = 8.2Hz). 13C NMR (CDCl3, 50 MHz) δ: 18.67, 31.86, 69.99, 75.91, 118.94, 121.36, 124.36, 126.44, 127.41, 127.45, 128.18, 128.29, 132.07, 133.10, 134.06, 140.10.
4.1.6 2-(1-bromo-naphthalen-2-yl)-4,5-dimethyl-3,6-dihydro-2H-pyran (10g)
Liquid, 1H NMR (CDCl3, 200 MHz) : 1.66 (s, 3H), 1.77 (s, 3H), 2.10 (m, 2H), 4.13-4.38 (m, 2H), 5.23 (dd, 1H, J = 3.6Hz, J = 10.2Hz), 7.47-7.64 (m, 2H), 7.70-7.89 (m, 3H), 8.35 (dd, 1H, J = 0.8Hz, J = 8.2Hz). 13C NMR (CDCl3, 100 MHz) : 14.03, 18.46, 36.95, 70.50, 76.52, 121.35, 124.12, 124.49, 124.61, 126.48, 127.45, 127.53, 128.25, 128.37, 132.16, 134.14, 140.28. Anal. Calcd for C17H17BrO: C, 64.37; H, 5.40 Found: C, 64.52; H, 5.25.
4.1.7 4-methyl-phenanthrene (11c)
Solid, mp 52-54 °C, 1H NMR (CDCl3, 400 MHz) δ: 3.17 (s, 3H), 7.50 (m, 2H), 7.59-7.67 (m, 2H), 7.71 (s, 2H), 7.79 (m, 1H), 7.94 (dd, 1H, J = 2Hz, J = 8.4Hz), 8.94 (d, 1H, J = 8Hz). 13C NMR (CDCl3, 100 MHz) δ: 27.37, 125.52, 125.74, 125.83, 127.04, 127.41, 127.47, 127.96, 128.66, 130.03, 131.18, 131.62, 133.44, 133.69, 135.49.
4.1.8 1,2-dimethyl-phenanthrene (11h)
Solid, mp 141-143 °C, 1H NMR (CDCl3, 200 MHz) : 2.54
(s, 3H), 2.66 (s, 3H), 7.47 (dd,1H, J = 8.4Hz), 7.54-7.64 (m, 2H), 7.76 (d, 1H, J = 9.2Hz), 7.87 (d,1H, J = 8.4Hz), 8.02 (d,1H, J = 9.2Hz), 8.49 (d, 1H, J = 8.4Hz), 8.67 (d, 1H, 8Hz).
4.1.9 1,2,3,4,4a,9,10,10a-octahydro-phenanthrene (17)
Liquid, 1H NMR (CDCl3, 400 MHz) : 1.12-1.51 (m, 6H), 1.77 (m, 3H), 1.90 (m, 1H), 2.25 (m 1H), 2.44 (dd, 1H, J = 3.2H, J = 12.8Hz), 2.78-2.96 (m, 2H), 7.06-7.15 (m, 3H), 7.29 (d, 1H, J = 7.6Hz). 13C NMR (CDCl3, 100 MHz) : Anal. Calcd for C14H18O: C, 90.26; H, 9.74 Found: C, 90.57; H, 9.49. HRMS: calcd for C14H19 [M+H]+ 187.1489 found 187.1484.
PAH = Polycyclic aromatic hydrocarbons, DMF = Dimethylformamide, TBAC = Tetrabutylammonium chloride, THF = Tetrahydrofuran, RCM = Ring-closing metathesis.
All authors are thankful to Prof. Jayanta Kumar Ray, Former Professor, Dept. of Chemistry, IIT Kharagpur, India, (popularly known as J. K. Ray) for providing his laboratory, instrumental facility, and valuable suggestion to prepare this manuscript.
Applicable, Selective 1HNMR and 13CNMR of synthesized compounds are available as Supplementary Information.
Conflict of Interest
There is no conflict of interest.
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Dr. Rathin Jana, FICS, is presently working as an Assistant Professor in Chemistry, Departnt of chemistry, Shahid MatanginiHazra Govt. college for women, nimtouri, West Bengal, India. He got his Ph.D degree from IIT, kharagpur, in 2010, M.Sc in organic chemistry in 2005 from Vidyasagar University and B. Sc in Chemistry from Haldia Government college under Vidyasagar University in 2003. His research interests are on synthesis of heterocyclic and carbocyclic compounds by palladium catalyzed reactions. He is Fellow and Life member of Indian Chemical Society (FICS) since 2020.
Dr. Mitali Dewan, is presently working as an Assistant Professor in Chemistry, Departnt of chemistry, Shahid Matangini Hazra Govt. college for women, nimtouri,West Bengal, India. She got his Ph.D degree from University of Culcutta in 2021, M.Sc in organic chemistry in 2007 from University of Culcutta and B. Sc in Chemistry from Vivekananda College under University of Culcutta in 2005. His research interests are on synthesis and application of polymer.
Dr. Gourisankar Roymahapatra, FICS, FIC, is presently working as an Associate Professor in Chemistry, Department of Applied Science, Haldia Institute of Technology, West Bengal, India. He got his Ph.D from Jadavpur University, in 2014, M.Sc in Physical Chemistry in 2003 from DAV PG College at Kanpur under CSJM University, India, B. Sc in Chemistry from Vidyasagar University in 2000. His research interests are on N-Heterocyclic Carbene (NHC) complexes, Catalysis, Antibiotics, Anti-carcinogenic and DFT studies, Molecular modeling, Gas adsorbent, Hydrogen fuel, and Metal-oxide Thin Film. He has teaching and industry experience more than 17 years. He served as a Senior Chemist in MCC PTA Chem. Corp. Pvt. Ltd India (MCPI), Haldia from December-2003- March’2011. He is Fellow and Life member of Indian Chemical Society (FICS) since 2012. He got ‘Distinguished Young Scientist Award in Chemiatry -2014” from ‘World Science Congress’, India, ‘Rasayan Ratna 2017' from SONAR TORI, Purba Medinipur, West Bengal, and prestigious ‘Bharat Gaurabh Award – 2018’ from IISF, India, elected Fellow of Institute of Chemists (India) (FIC) in 2019. He is the elected Vice-president of Haldia Vigyan Parishad (HVP) from 2018-20 and 2020-22. He was awarded as Par Excellence in NCQC-2007and as Gold in CCQC-2010 by Quality Circle Forum in India (QCFI). Recently he was selected as the joint guest editor of Journal of the Indian Chemical Society for Prof. D. C. Mukherjee special issue (2021) published by The Indian Chemical Society and Elsevier.
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