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Mn(OAc)3–Mediated Phosphonation–Lactonization of Cite this: DOI: 10.1039/x0xx00000x

Received 00th January 2012, Accepted 00th January 2012 DOI: 10.1039/x0xx00000x

Alkenoic Acids: Synthesis of Phosphono-γ-butyrolactones Yuzhen Gao,a Xueqin Li,a Jian Xu,a Yile Wu,a Weizhu Chen,a,b Guo Tang,a,* and Yufen Zhaoa,c Dedication to Professor Chengye Yuan on his 90th birthday

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A new, general method for the synthesis of phosphono-γbutyrolactones has been achieved through Mn(OAc)3mediated radical oxidative phosphonation and lactonization of alkenoic acids with H-phosphonates and H-phosphine oxide. Mn(OAc)3 can be readily prepared from Mn(OAc)2 in laboratory. This transformation allows the direct formation of a P-C bond and the construction of a lactone ring in one reaction. The butyrolactone framework is widely found in many biologicallyactive natural compounds, among which γ-lactone 5-phosphonates (A) and β-phosphono-γ-butyrolactones (B) have shown antiviral activity or are used as intermediates for the synthesis of αmethylene-γ-lactone, butenolide, and nucleoside analogs (Scheme 1).1 Because of the current interest in these two classes of pharmacologically- and synthetically-important phosphonate derivatives, various methods have been reported for the synthesis of such heterocyclic phosphonates.2 However, many currently accessible synthetic methods are impractical, for example, in terms of efficiency and environmental considerations. It is therefore important to develop a concise method for the synthesis of such molecules.

particular, Mn(OAc)3-promoted phosphonation is one of the most important methods used for the formation of carbon–phosphorus bonds.4 Herein, we describe a new method for the synthsis of phosphono-γ-butyrolactones via Mn(OAc)3–mediated radical oxidative phosphonation–lactonization of alkenoic acids. Electrophile-mediated cyclization of alkenes bearing a carboxylic acid pendant group has been increasingly exploited as attractive route to the synthesis of hydro-, trifluoro-, carbo- and halosubstituted lactones during recent years.8 We reasoned that generating directly the radicals D and E by addition of phosphorous radical C onto an olefin-acid would produce cationic intermediates through single-electron oxidation ultimately leading to the formation of endo and exo phosphono-γ-butyrolactones.4e,4g This transformation allows the direct formation of a P-C bond and the construction of a lactone ring in one reaction (Scheme 2).

Scheme 1. Biologically active phosphonobutyrolactones.

Scheme 2. Possible pathways in the reaction between a phosphorus radical and an unsaturated acid.

Reactions involving organophosphorus radicals have a long history, and these are useful reactive species in synthetic organic chemistry. It has been found that many salts such as silver,3 manganese4 and peroxide5 can react with R2P(O)H to form the corresponding phosphorus radical that promoted phosphorus radical addition chemistry.6 Economically and environmentally acceptable manganese salts are attractive because manganese is abundant.7 In

This idea was first examined by using diisopropyl Hphosphonate (1a) and 4-phenylpent-4-enoic acid (2a) as reaction partners (Table 1). When Mn(OAc)3·2H2O was chosen as the oxidant and HOAc as the solvent, the product 3a was obtained in 74% yield at 60oC under a nitrogen atmosphere (entry 1). However, the yield of product 3a decreased when the temperature was raised to

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80oC or decreased to room temperature (entries 2 and 3). The reaction was then performed in a variety of solvents (entries 4–6), such as acetonitrile (CH3CN), N-methyl-2-pyrrolidone (NMP) and N, N-dimethylformamide (DMF), giving product 3a in 68%, 55% and 50% yield, respectively. Unfortunately, the yield of product 3a decreased when 2 equivalents of CH3COONa or CH3COONH4 were added in the reaction (entries 7 and 8). Ishii and co-workers reported that Mn3+ generated in situ from Mn2+ under air efficiently catalyzes the addition of HP(O)(OR)2 to alkenes through a radical process.4d In our reaction, only 8% product was obtained when the reaction was performed in the open air with 0.05 equivalent of Mn(OAc)2·4H2O (entry 9), and no product was observed when 2 equivalents of MnO2 were used as oxidant instead of air (entry 10).4f Moreover, no desired product was obtained when 2.0 equiv of TEMPO was added into the reaction using the optimal conditions (entry 11). It was suggested that the phosphonation–lactonization of alkenoic acids might proceed via a radical pathway. After optimization of the reaction conditions, we established a highly efficient route to the phosphonation–lactonization of alkenoic acids. The optimal reaction conditions are: 3.0 equiv of Mn(OAc)3·2H2O as the oxidant, and HOAc as the solvent at 60oC for 8 h under a nitrogen atmosphere (entry 1)

unactivated 4-pentenoic acid to give product 3i in 35% yield. Table 2. Reaction of P(O)-H compounds with terminal alkenoic acids.

O P(O-i-Pr)2 O

O

Ph

Ph

Ph

3g 65%

Additive (equiv)

Solvent

T [oC]

Yield[%]

1 2 3 4 5 6 7b 8c 9d

Mn(OAc)3·2H2O (3) Mn(OAc)3·2H2O (3) Mn(OAc)3·2H2O (3) Mn(OAc)3·2H2O (3) Mn(OAc)3·2H2O (3) Mn(OAc)3·2H2O (3) Mn(OAc)3·2H2O (3) Mn(OAc)3·2H2O (3) Mn(OAc)2·4H2O (0.05) Mn(OAc)2·4H2O (0.05) + MnO2 (2) Mn(OAc)3·2H2O (3) + TEMPO (2)

CH3COOH CH3COOH CH3COOH CH3CN NMP DMF CH3COOH CH3COOH DMSO

60 80 rt 60 60 60 60 60 100

74 63 trace 68 55 50 36 51 8

CH3COOH

60

trace

CH3COOH

60

0

11

a Reaction conditions: 1a (0.6 mmol), 2a (0.3 mmol), additive in solvent (2 mL) stirring under nitrogen for 8 h. Oil bath temperature. Yield of the isolated product. b Add 0.6 mmol of CH3COONa. c Add 0.6 mmol of CH3COONH4. d Under air.

The results of exo-selective phosphonation–lactonization for terminal alkenoic acids 2 with different H–phosphonates 1 can be summarized as follows. As shown in Table 2, diisopropyl, diethyl, dimethyl, dibenzyl H–phosphonates all could be used as substrates, generating the corresponding products (3a-3f) in 65−82% isolated yields. It is worth noting that ethoxyphenylphosphine oxide (1e) and diphenylphosphine oxide (1f) can be also applied in the preparation of γ-lactone 5-phosphonates in 65% and 77% yield, respectively. 4Aryl-4-pentenoic acid derivatives were found to undergo the desired transformation to give the corresponding products (3a-3h) in good yields. The present exo-selective phosphonation is also applicable to

2 | J. Name., 2012, 00, 1-3

O

Ph

P(OBn)2 O

O

O

Ph

3h 77%

O

Ph P

Ph

O

Ph

3f 82%

O

OEt P

O

O P(OMe)2

O

OMe

3c 65%

3e 74%

O

O

F

O

O P(OEt)2

O

P(O-i-Pr)2 O

3b 67%

3d 72%

Entry

O

O

Table 1. Reaction conditions optimization.a

10

O

3a 74%

O

O P(O-i-Pr)2

O

P(O-i-Pr)2

Ph O

O

H

3i 35%

Next, we investigated endo-selective phosphonation–lactonization for alkenoic acids 4 with different P(O)-H compounds (Table 3). The reaction of (E)-4-phenyl-3-butenoic acids (4a) and diisopropyl H– phosphonate gave the corresponding endo-product 5a in 63% isolated yield. Variation of the position of the methyl group on the benzene ring (4b-4d) had little influence on the reaction efficiency (5b-5d). (E)-4-Aryl-3-butenoic acids with electron-donating (alkyl and methoxyl) groups on the benzene ring produced the desired products in good yields (5b-5f). A strongly electron-withdrawing trifluoromethyl group led to the formation of product 5g in much lower yield. Aryl rings with halogen substitutions also performed well in the reaction for both the bromo (70% yield; 5h) and chloro (53% yield; 5i) analogues. Moreover, alkenoic acids with naphthene and thiophene also reacted smoothly with diisopropyl Hphosphonate to afford products 5j and 5k, respectively, in 33% and 44% yields. These reaction products were accompanied by unidentified byproducts, and no alkenoic acids were recovered. It is noteworthy that aliphatic alkenoic acids can also participate in lactonization with slightly lower yields, giving products (5m, 5n) in 47% and 40% yield, respectively. The phosphono-γ-lactonization of (E)-4-methyl-4-phenyl-3-pentenoic acid (4l) and 3cyclohexylidenepropanoic acid (4m) gave endo-products 5l and 5m with a quaternary carbon center. Furthermore, the present protocol enables the synthesis of six-membered ring lactones (5q-5t) indicating that phosphono-δ-lactones are accessible under the standard reaction conditions. Diphenylphosphine oxide was used in the lactonization of internal alkenoic acids process, and led to the formation of products (5n-5s) in 80-40% yield indicating that the reactivities of these P(O)-H compounds are almost independent of the alkoxyl and alkyl moieties. The structure of 5o was unequivocally confirmed to be the trans-formation on the lactone ring by single-crystal X-ray analysis (see ESI).

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Notes and references O P(O-i-Pr)2

O

O

O

O

O

O

O

O

O

O

Br

O

5p 58%

O

O

Ph

(a) Y. M. Li, M. Sun, H. L. Wang, Q. P. Tian and S. D. Yang, Angew. Chem., Int. Ed., 2013, 52, 3972; (b) C. B. Xiang, Y. J. Bian, X. R. Mao and Z. Z. Huang, J. Org. Chem., 2012, 77, 7706; (c) B. Zhang, C. G. Daniliuc and A. Studer, Org. Lett., 2014, 16, 250.

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(a) X. Q. Pan, L. Wang, J. P. Zou and W. Zhang, Chem. Commun., 2011, 47, 7875; (b) X. J. Mu, J. P. Zou, Q. F. Qian and W. Zhang, Org. Lett., 2006, 8, 5291; (c) T. Kagayama, A. Nakano, S. Sakaguchi and Y. Ishii, Org. Lett., 2006, 8, 407; (d) O. Tayama, A. Nakano, T. Iwahama, S. Sakaguchi and Y. Ishii, J. Org. Chem., 2004, 69, 5494; (e) Y. Gao, J. Wu, J. Xu, X. Wang, G. Tang and Y .Zhao, Asian J. Org. Chem., 2014, 3, 691; (f) H. C. Fisher, O. Berger, F. Gelat and J. L. Montchamp, Adv. Synth. Catal., 2014, 356, 1199; (g) Y. Gao, J. Wu, J. Xu, P. Zhang, G. Tang and Y .Zhao, RSC Adv., 2014, 4, 51776.

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(a) Z. Zhao, W. Xue, Y. Gao, G. Tang and Y. Zhao, Chem. Asian J., 2013, 8, 713; (b) J. Xu, P. Zhang, X. Li, Y. Gao, J. Wu, G. Tang and Y. Zhao, Adv. Synth. Catal., 2014, 356, 3331.

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Reviews on P-centered radicals: (a) D. Leca, L. Fensterbank, E. Lacote and M. Malacria, Chem. Soc. Rev. 2005, 34, 858; (b) S. Van der Jeught

5o 80% O Ph P Ph

Me Me

Ph

O

O

Ph

5r 71%

O P(O-i-Pr)2 O

5s 70% a

3

O

5q 63% O Ph P Ph

O

(a) A. Arnone, P. Bravo, M. Frigerio, F. Viani and C. Zappalà, Synthesis, 1998, 1511; (b) H. Krawczyk, K. Wasek, J. Kedzia, J. Wojciechowski and W. M. Wolf, Org. Biomol. Chem., 2008, 6, 308; (c) A. Arnone, P. Bravo, M. Frigerio, A. Mele, B. Vergani and F. Viani, Eur. J. Org. Chem., 1999, 2149; (d) Frings, I. Thomé, I. Schiffers, F. Pan and C. Bolm, Chem. Eur. J., 2014, 20, 1691; (e) A. A. Prishchenko, M. V. Livantsov, O. P. Novikova, L. I. Livantsova and V. S. Petrosyan, Heteroatom Chemistry, 2008, 19, 418; (f) P. Dauban and R. H. Dodd, J. Org. Chem., 1997, 62, 4277.

O Ph P Ph O

O Ph P Ph

O

2

5l 68%

5n 40%

O Ph P Ph

(a) G. M. Blackburn, F. Eckstein, D. E. Kent and T. D. Perrée, Nucleosides Nucleotides, 1985, 4, 165; (b) T. Janecki, R. Bodalski, M. Wieczorek and G. Bujacz, Tetrahedron, 1995, 51, 1721; (c) T. Janecki and E. Błaszczyk, Synthesis, 2001, 403; (d) T. Janecki, E. Błaszczyk, K. Studzian, A. Janecka, U. Krajewska and M. Różalski, J. Med. Chem., 2005, 48, 3516; (e) T. Janecki and R. Bodalski, Tetrahedron Lett., 1991, 32, 6231.

Ph O Me

O

O Ph P Ph

O

1

P(O-i-Pr)2

5k 44%b

5m 47%

Cl

O

S

P(O-i-Pr)2

Key Laboratory of Bioorganic Phosphorus Chemistry and Chemical Biology (Ministry of Education), Department of Chemistry, Tsinghua University, Beijing 100084, China

5i 53%

O

O

O

O

O

O

P(O-i-Pr)2

5j 33%

O

Br

O

P(O-i-Pr)2 O

c

Electronic Supplementary Information (ESI) available: Experimental procedures for the synthesis, spectral data and NMR spectra of compounds 3a-3i, 5a-5t. See DOI: 10.1039/c000000x/

P(O-i-Pr)2

5h 70%

5g 31%

Third Institute Of Oceanography, State Oceanic Administration, Xiamen, Fujian 361005, China

OMe

O P(O-i-Pr)2

CF3

b

5f 71%a

O P(O-i-Pr)2

O

O

O

5e 84%

O

O

P(O-i-Pr)2

O

Me 5d 56%

Me

O P(O-i-Pr)2

O

O

5c 60%

O

P(O-i-Pr)2

Department of Chemistry, College of Chemistry and Chemical Engineering, and the Key Laboratory for Chemical Biology of Fujian Province, Xiamen University, Xiamen, Fujian 361005, China Fax: (86)592-2185780; E-mail: [email protected]

O

O

Me

5b 61%

5a 63%

a

P(O-i-Pr)2

P(O-i-Pr)2

O

O

O

O

O

Ph

5t 55%

trans/cis = 1:0.45. b trans/cis = 1:0.3.

In conclusion, we have developed Mn(OAc)3-mediated radical oxidative phosphonation–lactonization of both terminal and internal alkenoic acids under relatively mild conditions. In particular, both γand δ-lactone phosphonates are accessible under the standard reaction conditions, using substrates bearing many functional groups and reacting in a diastereoselective manner.

Acknowledgements

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Table 3. Reaction of H-phosphonates with internal alkenoic acids.

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(a) T. D. Lash, Chem. Asian J., 2014, 9, 682; (b) J. M. Concellón, H. Rodríguez-Solla and V. Del Amo, Chem. Eur. J., 2008, 14, 10184.

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and C. V. Stevens, Chem. Rev., 2009, 109, 2672; (c) S. Marque and P. Tordo, Top. Curr. Chem., 2005, 250, 43; (d) M. Mondal and U. Bora, RSC Adv., 2013, 3, 18716.

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Mn(OAc)3-mediated phosphonation-lactonization of alkenoic acids: synthesis of phosphono-γ-butyrolactones.

A new, general method for the synthesis of phosphono-γ-butyrolactones has been achieved through Mn(OAc)3-mediated radical oxidative phosphonation and ...
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