Startseite Synthesis of polycyclic phosphonates via an intramolecular Diels-Alder reaction of 2-benzoylbenzalaldehyde and alkenyl phosphites
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Synthesis of polycyclic phosphonates via an intramolecular Diels-Alder reaction of 2-benzoylbenzalaldehyde and alkenyl phosphites

  • Kenji Yamana und Hirofumi Nakano
Veröffentlicht/Copyright: 17. Mai 2019
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Heterocyclic Communications
Aus der Zeitschrift Heterocyclic Communications Band 25 Heft 1

Abstract

In this paper, we present a Lewis-acid-promoted reaction of 2-benzoylbenzaldehyde and trialkenyl phosphites, which resulted in the formation of polycyclic phosphonates. The reaction proceeded via nucleophilic attack of trialkenyl phosphite on the carbonyl carbon of 2-benzoylbenzaldehyde. The subsequent intramolecular Diels-Alder reaction led to the formation of the cyclic phosphonate.

Keywords: Intramolecular cycloaddition; Diels-Alder reaction; oxaphosphinane; isobenzofuran; cyclic phosphonate

Cyclic phosphonates are often utilized as key intermediate reagents (synthetic intermediates) in the preparation of synthetically useful products and biologically active compounds [1,2]. Therefore, the synthesis of these compounds has attracted a great deal of research attention in the fields of synthetic organic, bioorganic, and medicinal chemistry [3, 4, 5, 6]. Moreover, the development of new methods for the preparation of cyclic phosphonates has become very important in organic chemistry. For this purpose, the chemistry of isobenzofuran [7,8,9] and the intramolecular Diels-Alder reaction [10,11] are extremely interesting from a theoretical point of view. They represent a possible way to synthesize pharmaceutical candidate compounds, such as natural products and biologically active compounds with complicated structures in only a few short steps [3,12, 13, 14, 15, 16, 17, 18, 19, 20,]. For example, the synthesis of alkaloid derivatives using Lewis acids has been reported by Yilin et al. [21,22]. Previously, we reported the formation of dialkyl isobenzofuran-1-ylphosphonates by the reaction between o-phthalalde-hyde and trialkyl phosphites in the presence of a Lewis acid (Scheme 1) [23,24].

In this study, we attempted to apply a Lewis-acid-promoted reaction of aromatic aldehydes and alkenyl phosphites to establish a new method for the one-step synthesis of polycyclic phosphonates.

Unfortunately, the reaction of o-phthalaldehyde 1 with triallyl phosphite 2a or tributenyl phosphite 2b failed to produce the intramolecular Diels-Alder adducts 4a and 4b (Scheme 2). We considered the possibility that isobenzofuran derivatives 3a and 3b were formed as intermediates, but decomposed due to their instability under these reaction conditions. Because of the low dienophilicity of the C=C bond of allyl and butenyl groups, the intramolecular Diels-Alder reaction of 3 did not proceed smoothly. On the other hand, adducts 5a and 5b were formed from the reaction of 1 with trialkenyl phosphite and N-phenylmal-eimide via intermediates 3a and 3b. However, we considered the possibility to obtain the intramolecular adducts by stabilizing the intermediates 3a and 3b.

Considering the previously reported stabilization effect of a phenyl group on the intermediate isobenzofuran-1-ylphosphonate [25], a similar approach was employed in this study. It was expected that the replacement of 1 by 2-benzoylbenzaldehyde 6 would stabilize the intermediates, isobenzofuran derivatives 7a and 7b, due to a resonance effect derived from the phenyl group. The intramolecular adduct 9b (Scheme 3, 31% yield) was generated from the intramolecular Diels-Alder reaction of isobenzofuran derivative 7b and the subsequent aromatization of the product 8b. However, these reaction conditions did not yield the intramolecular adduct 9a. This suggested that the strain of the 5-membered ring in 8a is stronger than that of the 6-membered ring in 8b.

Scheme 1
Scheme 1
Scheme 2
Scheme 2
Scheme 3
Scheme 3

The fact that the yield of the intermolecular adduct 5a (47%) from triallyl phosphite 2a was better than that of 5b (27%) from tributenyl phosphite 2b (Scheme 2) indicated that the reaction of 2a proceeded more smoothly than that of 2b because the allyl cation is more stable than the butenyl cation.

As previously reported, the rate limiting step in the formation of isobenzofuran-1-ylphosphonates is the alkyl group elimination from the trialkyl phosphite [25]. Moreover, the reaction proceeds more easily and the yield is increased when the alkyl group is smaller [Scheme 1, R1 = H, R2 = Me (80%), Et (71%), Pr (67%), and i-Pr (55%); endo/exo total yield). Similarly, the yield of polycyclic phosphonates should improve when the butenyl group of the trialkenyl phosphite is converted to a methyl group.

Therefore, dibutenyl methyl phosphite 2c, where one of the butenyl groups is replaced by a methyl group, was employed in the reaction. This led to an increase in the total yield of the reaction to 67%, with 9b (48%) being the major product after elimination of the methyl group (Scheme 4).

In summary, a new method for the synthesis of polycyclic phosphonates was developed, involving the treatment of 2-benzoylbenzaldehyde 6 with alkenyl phosphites, such as 2b and 2c. Polycyclic phosphonates 9b and 9c were obtained via an intramolecular cycloaddition in only one step. These reactions provide a new approach to the generation of cyclic phosphonates.

Experimental Details

1H NMR (400 MHz) and 13C NMR (100 MHz) spectra were recorded in CDCl3 on a Bruker AVANCE III instrument. Tetramethylsilane was employed as an internal standard. The melting points were determined using a Yanako micro melting point apparatus and were uncorrected. High-resolution mass spectra were obtained using a JEOL JMS-T100GCV (EI) and microOTOF-QII (ESI).

General Procedure for the Preparation of Intramolecular Diels-Alder Adducts

BF3•OEt2 (1 mmol) was added to a solution of 2-benzoylbenzaldehyde 6 (1 mmol) in acetonitrile (3 mL) at

Scheme 4
Scheme 4
Table 1

Yields of intramolecular Diels-Alder adducts (9a-c) by the reaction of 2-benzoylbenzaldehyde (6) and phosphites (2a-c)a

EntryPhosphitesAdductsYieldsb ( % )
12a9a-
22b9b31
32c9b, 9c48, 19

  1. aReaction conditions: BF3 ∙ OEt2 and 2-benzoylbenzaldehyde (1 equiv), MeCN, 0 °C, 0.5 h, followed by phosphites (1 equiv), 25 °C, 48 h. bIsolated.

0 °C. After stirring at this temperature for 0.5 h, alkenyl phosphite 2b or 2c (1 mmol) was added and the mixture was stirred at 25 °C for 48 h. HCl solution was added to quench the reaction, and the organic layer was extracted with CH2Cl2, washed with NaHCO3, dried over anhydrous Na2SO4, and concentrated in vacuo. The residue was chromatographed on silica gel (AcOEt:Hexane = 1:1) to give 9b or 9c.

1-(But-3-en-1-yloxy)-6-phenyl-1H,3H,4H-1l5-naphtho[1,2-c][1,2]oxaphosphinin-1-one (9b)

The compound was obtained as a colorless oil; 1H NMR (400 MHz, CDCl3): δ 8.62 (d, 1H, J = 8.5 Hz), 7.87 (d, 1H, J = 8.5 Hz), 7.62 (t, 1H, J = 7.4 Hz), 7.43−7.52 (m, 6H), 7.23 (d, 1H, J = 5.2 Hz), 5.81 (ddt, 1H, J = 17.1, 10.3, 6.8 Hz), 5.13 (d, 1H, J = 17.2 Hz), 5.08 (d, 1H, J = 10.2 Hz), 4.62-4.68 (m, 2H), 4.29−4.37 (m, 1H), 4.23 (ddd, 1H, J = 13.9, 10.0, 6.9 Hz), 3.35−3.43 (m, 1H), 3.14 (ddd, 1H, J = 17.2, 7.3, 4.0 Hz), 2.48−2.53 (m, 2H); 13C NMR (100 MHz, CDCl3): δ 145.3 (d, 4JC,P =3.2 Hz), 142.0 (d, 2JC,P = 6.3 Hz), 139.5, 133.6, 133.4 (d, 2JC,P = 9.8 Hz), 130.9 (d, 3JC,P = 12.2 Hz), 129.7, 128.4, 128.0, 127.8, 127.2 (d, 3JC,P = 14.9 Hz), 127.1 (d, 3JC,P = 5.8 Hz, C-5), 126.8 (C-7), 126.4 (C-8), 120.1 (d, 1JC,P = 174.7 Hz, C-10a), 117.7 (CH2=CH-), 65.9 (d, 2JC,P = 6.0 Hz, CH2), 65.3 (d, 2JC,P = 7.0 Hz, CH2), 34.9 (d, 3JC,P = 6.3 Hz, CH2), 32.3 (d, 3JC,P = 7.1 Hz, C-4). HRMS (EI) Calcd for C19H17NO3P (M+): 364.1228. Found: 364.1226.

1-Methoxy-6-phenyl-1H,3H,4H-1l5-naphtho[1,2-c][1,2] oxaphosphinin-1-one (9c)

The compound was obtained as a colorless oil; 1H NMR (400 MHz, CDCl3): δ 8.61 (d, 1H, J = 8.5 Hz, ArH), 7.87 (d, 1H, J = 8.4 Hz, ArH), 7.63 (t, 1H, J = 7.7 Hz, ArH), 7.44−7.53 (m, 6H, ArH), 7.24 (d, J = 5.2 Hz, 1H, ArH), 4.62 (m, 2H, CH2), 3.89 (d, 3H, 3JP-O-C-H = 11.4 Hz, CH3), 3.34−3.41 (m, 1H, CH2), 3.14−3.21(m, 1H, CH2); 13C NMR (100 MHz, CDCl3): δ 145.4 (d, 3JC-P =3.6 Hz, ArC), 142.1 (d, 2JC-P =6.4 Hz, ArC), 139.5 (ArC), 133.4 (d, 2JC-P =9.9 Hz, ArC), 130.9 (d, 3JC-P =12.1 Hz, ArC), 129.7 (ArC), 128.4, 128.0, 127.8, 127.2 (d, 3JC-P =14.7 Hz, ArC), 126.9 (d, 3JC-P=5.7 Hz, ArC), 126.8 (ArC), 126.4, 120.0 (d, JC- P = 174.1 Hz, ArC-P), 66.0 (d, 2JC-O-P = 5.9 Hz, CH2), 52.7 (d, 3JC-O-P = 6.8 Hz, CH2), 32.3 (d, 3JC-O-P = 7.1 Hz, CH2). HRMS (EI) Calcd for C19H17NO3P (M+): 324.0915. Found: 324.0907.

Bis(but-3-enyl) methyl phosphite (2c)

The compound was obtained as a colorless oil; 1H NMR (400 MHz, CDCl3): δ 5.76−5.85 (m, 2H), 5.06−5.14 (m, 4H), 3.51 (dt, 4H, J =7.8, 6.9 Hz), 3.51 (d, 3H, J = 10.4 Hz), 2.36−2.45 (m, 4H); 13C NMR (100 MHz, CDCl3): δ 134.5, 117.7, 61.7 (d, 2JC,P = 11.7 Hz), 49.0 (d, 2JC,P = 9.3 Hz), 35.6 (d, 4JC,P = 5.0 Hz). HRMS (ESI Negative) Calcd for C19H17NO3P (M+H-): 205.0994. Found: 205.0637.

Bis(prop-2-enyl) [(3aR*,4S*,9S*,9aR*)-1,3-dioxo-2-phenyl-1,2,3,3a,9,9a-hexahydro-4H-4,9-epoxybenzo[f] isoindol-4-yl]phosphonate (endo) (5a)

The compound was obtained as a colorless oil; 1H NMR (400 MHz, CDCl3): δ 7.52–7.61 (m, 1H), 7.34–7.40 (m, 3H), 7.25–7.28 (m, 3H), 6.38–6.42 (m, 2H), 6.02–6.11 (m, 1H), 5.87–5.96 (m, 2H), 5.44–5.49 (m, 1H), 5.28–5.35 (m, 2H), 5.20–5.22 (m, 1H), 4.87–4.98 (m, 2H), 4.64–4.76 (m, 2H), 4.27 (dd, 1H, J = 9.0, 8.6 Hz), 4.07 (dd, 1H, J = 8.5, 5.8 Hz); 13C NMR (67.80 MHz, CDCl3): δ 172.6, 171.5, 140.7, 140.7, 139.7, 139.6, 132.8, 132.7, 132.4, 132.4, 130.8, 129.0, 128.9, 128.7, 128.6, 126.3, 125.8, 122.1, 121.3, 118.7, 118.5, 86.2 (d, JC,P = 191.3 Hz), 81.6 (d, 3JC,P = 15.4 Hz), 68.5 (d, 2JC,P = 6.0 Hz), 68.0 (d, 2JC,P = 6.2 Hz), 50.7 (d, 3JC,P = 6.6 Hz), 49.7 (d, 3JC,P = 4.4 Hz). HRMS (ESI Negative) Calcd for C24H21NO6P (M-H+): 450.1106. Found: 450.1169.

Bis(but-3-enyl) [(3aR*,4S*,9S*,9aR*)-1,3-dioxo-2-phenyl-1,2,3,3a,9,9a-hexahydro-4H-4,9-epoxybenzo[f] isoindol-4-yl]phosphonate (endo) (5b)

The compound was obtained as a colorless oil; 1H NMR (400 MHz, CDCl3): δ 7.55–7.58 (m, 1H), 7.33–7.39 (m, 3H), 7.24–7.26 (m, 3H), 6.38–6.41 (m, 2H), 5.81–5.91 (m, 2H), 5.66–5.76 (m, 1H), 5.01–5.20 (m, 4H), 4.47 (dt, 2H, J = 6.8, 8.0 Hz, 2H), 4.18–4.29 (m, 3H), 4.05 (dd, 1H, J = 5.8, 5.8 Hz), 2.56–2.61 (m, 2H), 2.41 (dt, 2H, J = 6.7, 6.7 Hz); 13C NMR (67.80 MHz, CDCl3): δ 172.6, 171.5, 140.8, 140.7, 139.8, 139.8, 133.5, 133.2, 130.8, 129.1, 129.0, 128.8, 128.7, 128.5, 126.3, 122.1, 121.2, 117.9, 117.7, 86.2 (d, JC,P = 191.1 Hz), 81.6 (d, 3JC,P = 15.3 Hz), 67.0 (d, 2JC,P = 6.5 Hz ), 66.7 (d, 2JC,P = 6.5 Hz), 50.7 (d, 3JC,P = 6.6 Hz), 49.7 (d, 3JC,P = 4.3 Hz), 35.1 (d, 3JC-P = 5.5 Hz), 34.8 (d, 3JC,P = 5.8 Hz). HRMS (ESI Negative) Calcd for C26H25NO6P (M-H+): 478.1419. Found: 478.1476.

Acknowledgements

We would like to thank Editage (www. editage.jp) for English language editing

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Received: 2018-11-01
Accepted: 2019-01-18
Published Online: 2019-05-17

© 2019 Kenji Yamana and Hirofumi Nakano, published by De Gruyter

This work is licensed under the Creative Commons Attribution 4.0 Public License.

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https://doi.org/10.1515/hc-2019-0011
Schlagwörter für diesen Artikel
Intramolecular cycloaddition; Diels-Alder reaction; oxaphosphinane; isobenzofuran; cyclic phosphonate
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  23. Facile One-pot Protocol of Derivatization Nitropyridines: Access to 3-Acetamidopyridin-2-yl 4-methylbenzenesulfonate Derivatives
  24. Naphthalene substituted benzo[c]coumarins: Synthesis, characterization and evaluation of antibacterial activity and cytotoxicity
  25. A Green Synthesis and Antibacterial Activity of N-Arylsulfonylhydrazone Compounds
  26. Preliminary Communications
  27. Facile Synthesis of Spiro[cyclohexane-1,3’-indoline]-2,2’-diones
  28. Research Article
  29. Synthesis and AChE inhibitory activity of N-glycosyl benzofuran derivatives
  30. [DMImd-DMP]: A highly efficient and reusable catalyst for the synthesis of 4H-benzo[b]pyran derivatives
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