Friedel–Crafts reaction catalyzed by perfluorinated rare earth metals

Journal of Fluorine Chemistry 116 (2002) 143±147

Friedel±Crafts reaction catalyzed by per¯uorinated rare earth metals Min Shi*, Shi-Cong Cui State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 354 Fenglin Lu, Shanghai 200032, China Received 4 April 2002; received in revised form 17 May 2002; accepted 12 June 2002

Abstract The Friedel±Crafts reaction of anisole with acetic anhydride can be carried out in the presence of per¯uorinated rare earth metal catalyst without organic solvent. Per¯uorodecalin (C10F18, cis- and trans-mixture) can be used as a ¯uorous phase solvent for this reaction. Whereas, the reaction of N,N-dimethylaniline with acetic anhydride did not give the corresponding Friedel±Crafts reaction product. On the other hand, the Friedel±Crafts reaction of N,N-dimethylaniline with ethyl glyoxylate was also examined in the presence of per¯uorinated Lewis acids. Three products were in fact formed at the same time. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Friedel±Crafts reaction; Solvent free; Ethyl glyoxylate; Anisole; Per¯uorinated rare earth metal catalyst

1. Introduction Friedel±Crafts acylation and alkylation are fundamental and useful reactions for introducing functional substituents to aromatic rings [1]. They are often applied to industrial production of pharmaceutical and agricultural chemicals, plastics, liquid crystals, etc. Friedel±Crafts reactions were originally performed using more than stoichiometrical amount of Lewis acids such as aluminum trichloride (AlCl3) because the Lewis acids are consumed by coordination with the produced aromatic ketones. But a large amount of AlCl3 and its waste after aqueous work-up procedures often cause serious environmental problems. Recently, Kobayashi and coworkers have published many papers related with the Lewis acids of rare earth metal tri¯ate [Ln(OTf)3]. They found that rare earth metal tri¯ate [Ln(OTf)3] worked ef®ciently as Lewis acids even in aqueous media or in the presence of amines. A catalytic amount of Ln(OTf)3 allows proceeding several synthetically useful reactions such as aldol condensation, Michael addition, allylation reaction, Mannich reaction or Diels±Alder reactions, etc. [2]. Rare earth metal tri¯ate is also a good catalyst for Friedel±Crafts reactions [3,4]. They demonstrated that in nitromethane (CH3NO2) or 1,2-dichloroethane (CH2Cl)2 a catalytic amount of Ln(OTf)3 (10 mol%) is enough to complete the Friedel±Crafts reaction. However, the organic solvent used * Corresponding author. Fax: ‡86-21-64166128. E-mail address: [email protected] (M. Shi).

in this reaction such as nitromethane (CH3NO2), 1,2dichloroethane (CH2Cl)2 is not an environment-benign solvent (eco-safer solvent) [5]. Thus, a solvent free or so called ``green'' Friedel±Crafts reaction process is required to be explored. On the other hand, per¯uorocarbon f1uids, especially perf1uoro-alkanes have some unique properties which make them attractive alternatives for conventional organic solvents [6]. They have limited miscibility with conventional organic solvents. The compounds functionalized with per¯uorinated groups often dissolve preferentially in ¯uorous solvents this can be used to extract ¯uorous components from reaction mixtures [7]. Therefore, the application of ¯uorous phase separation techniques in catalysis can be used to the per¯uorinated rare earth metals catalyzed Friedel± Crafts reaction. In this paper, we wish to report a green Friedel±Crafts reaction using per¯uorinated rare earth metals as catalysts under solvent free condition or in ¯uorous phase. 2. Results and discussion 2.1. Friedel±Crafts reaction of anisole with acetic anhydride under solvent free condition or in fluorous phase Kobayashi reported in 2000 that Sc(OSO2C8F17)3 [Sc(OPf)3]3 can be used as an ef®cient catalyst for the catalytic Diels±Alder or Aze Diels±Alder reaction [2-4]. Based on his results, we believe that such Lewis acids having

0022-1139/02/$ ± see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 2 - 1 1 3 9 ( 0 2 ) 0 0 1 2 6 - 4

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M. Shi, S.-C. Cui / Journal of Fluorine Chemistry 116 (2002) 143±147

Scheme 1.

Scheme 2.

per¯uorinated long carbon chains have stronger Lewis acidity than rare earth metal tri¯ate [Ln(OSO2CF3)3] and can act as a phase transfer catalyst (PTC) as well for some other organic reactions [2-4]. Thus, we prepared rare earth metal heptadeca¯uorooctanesulfonic acid salt [Ln(OSO2C8F17)3] [8] and used them to catalyze the Friedel± Crafts reaction under solvent free condition. The reaction was carried out in acetic anhydride using anisole as the substrate (Scheme 1). The results are presented in Table 1. We found that at higher temperature (100 8C) Yb(OSO2C8F17)3 is indeed more active than Yb(OSO2CF3)3 (Table 1, entries 4 and 5). Sc(OSO2CF3)3 is the most active catalyst for this reaction (Table 1, entry 6). Higher reaction temperature must be required in order to get higher yield of the Friedel±Crafts reaction product 1 (Table 1, entries 1±4). In general, moderate yields of Friedel±Crafts reaction product could be obtained using per¯uorinated rare earth metal catalyst under solvent free condition. We next tried the Friedel±Crafts reaction of anisole with acetic anhydride in ¯uorous phase (Scheme 2). Using per¯uoro(methylcyclohexane) (C7F14) or per¯uorodecalin (C10F18, cis- and trans-mixture) as the ¯uorous solvent, the ¯uorous phase is not miscible with aromatic substrate and acetic anhydride. It only dissolves the Ln(OSO2C8F17)3 catalysts. The ¯uorous layer can be easily isolated from the reaction mixture and reused to the next Friedel±Crafts reaction. Ln(OSO2C8F17)3 catalysts dissolve completely in per¯uorocabon. But we found that, during the repeated Friedel±Crafts reaction, the loss of ¯uorous solvent is very serious if using per¯uoro(methylcyclohexane) (C7F14) as the solvent because it is very volatile (b.p.: 76 8C). Per¯uorodecalin (C10F18, cis- and trans-mixture) is the best ¯uorous solvent for Friedel±Crafts reaction (Scheme 2). The ¯uorous phase with Ln(OSO2C8F17)3 catalyst is in the bottom layer, while the organic layer is on the top. Upon heating to 70 8C they can completely mix together to make the reaction take place. After cooling the reaction mixture to room temperaTable 1 Friedel±Crafts acylation of anisole with Ac2O Entry

Catalysta

Temperature (8C)

Time (h)

Yield (%)b

1 2 3 4 5 6

Yb(OTf)3 Yb(OTf)3 Yb(OTf)3 Yb(OTf)3 Yb(OPf)3 Sc(OPf)3

RT 50 50 100 100 100

24 24 48 48 48 48

15 20 25 45 50 62

a

The reaction was carried out in the presence of 0.1 mmol% of catalyst. b Isolated yield.

Table 2 Friedel±Crafts acylation of anisole with Ac2O in fluorous phase Run

Catalysta

Temperature (8C)

Time (h)

Yield (%)b

1 2 3

Yb(OPf)3 Yb(OPf)3 Yb(OPf)3

70 70 70

48 48 48

54 50 52

a b

The reaction was carried out in the presence of catalyst (0.1 mol%). Isolated yield.

ture (RT), the ¯uorous phase with Ln(OSO2C8F17)3 catalyst can separate from the organic layer return to the bottom layer. Based on the 19 F NMR spectroscopic data and GC± MS, no loss of catalyst or per¯uorodecalin to the organic phase can be detected. The isolated ¯uorous phase with Ln(OSO2C8F17)3 catalyst can be immediately used to the next Friedel±Crafts reaction without loss of activity (Table 2, runs 1±3). Herein, we found a very good ¯uorous phase solvent for rare earth metal catalyzed Friedel±Crafts reaction. The employed Yb(OSO2C8F17)3 catalyst can be easily isolated from the reaction mixture with ¯uorous phase. 2.2. The Friedel±Crafts reaction of N,N-dimethylaniline with acetic anhydride Besides anisole we also tried the Friedel±Crafts reaction of N,N-dimethylaniline with acetic anhydride under the same condition. But we found that none of the corresponding Friedel±Crafts product was formed at all. Many reaction products 2±6 were isolated after reaction and the product's distribution changes with the reaction time (Scheme 3). The results were shown in Table 3. The structures of 2±6 were determined by spectroscopic data. This reaction is not related with the Ln(OSO2C8F17)3 catalyst because in the absence of Yb(OSO2C8F17)3 the same products were formed. It also should be emphasized here that the reaction products of N,N-dimethylaniline with acetic anhydride can Table 3 The reaction of N,N-dimethylaniline with acetic anhydride Entry

Time (days)

Temperature (8C)

1 2 3 4 5

2 3 4 3 4

95 95 95 95 95

a

Isolated yield.

Yield (%)a 2

3

4

5

6

± 10 ± 10 ±

32 ± ± 17 ±

± 20 ± ± ±

± ± 8 ± ±

± ± 9 ± 2

M. Shi, S.-C. Cui / Journal of Fluorine Chemistry 116 (2002) 143±147

145

Scheme 3.

Scheme 4.

be signi®cantly affected by the very slight changes on reaction temperature and reaction time (Table 3). Namely, this reaction does not have reproducibility (Table 3, entries 2 and 4; Table 3, entries 4 and 5). Previous reports have disclosed that an electrontrasfer process take place in this reaction to give the corresponding complicated products [9]. The Friedel±Crafts reaction of N,N-dimethylaniline with acetic anhydride do not occur to produce the desired product. 2.3. The Friedel±Crafts reaction of N,N-dimethylaniline with ethyl glyoxylate at RT Using Ln(OSO2CF3)3 or Ln(OSO2C8F17)3 as a catalyst, we also examined the Friedel±Crafts reaction of N,Ndimethylaniline with ethyl glyoxylate. This is a new type of Friedel±Crafts reaction reported by Mikami et al. [10]. Recently, some papers disclosed that Cu(OTf)2 is also an effective catalyst for this reaction [11]. Thus, we spontaneously anticipate that Ln(OPf)3 or Ln(OTf)3 should also be a good catalyst for these reactions. The reaction was carried out in dichloromethane at RT in the presence of Ln(OPf)3 or Ln(OTf)3 (1.0 mol%) (Scheme 4). But in our experiment, we found that this reaction in general gave three products 7±9 in moderate yields. The expected Friedel±Crafts reaction product 7 is the major product. The results are presented in Table 4. Yb(OPf)3 and Yb(OTf)3 and Sc(OPf)3 have the similar activity for this reaction in dichloromethane (Table 4, entries 1±3). We believe that compound 8 is derived from

further Friedel±Crafts reaction of 7 with N,N-dimethylaniline in the presence of Lewis acid and compound 9 is derived from the hydrolysis of 8. It should be emphasized here that using LiOPf (LiOSO2C8F17) as a Lewis acid the reaction proceed in dichloromethane to give the products 7±9 in higher yields (Table 4, entry 4), although in ¯uorous phase or THF lower yields of 7±9 were obtained (Table 4, entries 5±6). In conclusion, we found that using Ln(OPf)3 as a catalyst the Friedel±Crafts reaction of anisole with acetic anhydride can be carried out under hazardous solvent (CH3NO2 or ClCH2CH2Cl) free condition. Per¯uorodecalin (C10F18, cisand trans-mixture) can be used as a ¯uorous phase solvent for the above Friedel±Crafts reaction by which the Ln(OPf)3 catalyst can be easily isolated for the next reaction. The Table 4 Friedel±Crafts acylation of N,N-dimethylaniline with ethyl glyoxylate Entry

Catalysta

1 2 3 4

Yb(OTf)3 Yb(OPf)3 Sc(OPf)3 Li(OPf)3

5

Li(OPf)3

6

Li(OPf)3 a b

Solvent

CH2Cl2 CH2Cl2 CH2Cl2 CH2Cl2

THF

Yield (%)b 7

8

9

28 30 31 56

7 8 8 8

8 8 8 8

27

6

8

9

±

±

The reaction was carried out in the presence of catalyst (1 mol%). Isolated yield.

146

M. Shi, S.-C. Cui / Journal of Fluorine Chemistry 116 (2002) 143±147

reaction of N,N-dimethylaniline with acetic anhydride do not give the Friedel±Crafts reaction product under the same conditions. The Friedel±Crafts reaction of N,N-dimethylaniline with ethyl glyoxylate gave three products in the presence of per¯uorinated catalysts. 3. Experimental section 3.1. General Melting points are uncorrected. 1 H and 13 C NMR spectra were recorded at 300 and 75 MHz, respectively. Mass spectra were recorded by EI method and HRMS was measured on a Finnigan MA‡ mass spectrometer. Organic solvents used were dried by standard methods when necessary. Commercially available reagents were used without further puri®cation. All reactions were monitored by TLC with Huanghai GF254 silica gel coated plates. Flash column chromatography was carried out using 200±300 mesh silica gel. Ln(C8F17SO3)3 was prepared from the reaction of C8F17SO3H with Ln2O3 according to the literature [8]. 3.2. Friedel±Crafts reaction of anisole with acetic anhydride To a solution of anisole (2 mmol, 0.22 ml) and acetic anhydride (1.85 mg, 2 ml) was added Yb(C8F17SO3)3 (3.4 mg, 0.002 mmol) and reaction mixture was stirred at 100 8C for 48 h. The reaction mixture was washed with water (10 ml  2) and extracted with dichloromethane (CH2Cl2). The solvent was removed under reduced pressure and the residue was puri®ed by a silica gel column chromatongraph (eluent: petroleum ether/EtOAc ˆ 5/1) to give the product 1 as a colorless liquid. 3.3. Friedel±Crafts reaction of N,N-dimethylaniline with acetic anhydride To a solution of N,N-dimethylaniline (242 mg, 2 mmol, 0.23 ml) and acetic anhydride (1.85 mg, 2 ml) was added Yb(C8F17SO3)3 (3.4 mg, 0.002 mmol) and reaction mixture was stirred at 100 8C for 48 h. The reaction mixture was washed with water (10 ml  2) and extracted with dichloromethane (CH2Cl2). The solvent was removed under reduced pressure and the residue was puri®ed by a silica gel column chromatongraph (eluent: petroleum ether/ EtOAc ˆ 1/2) to give products 2±6. N-Methyl-N-phenylacetamide 2. A colorless solid; m.p. 72±74 8C. IR (CHCl3) n 1654 cm 1 (C=O). 1 H NMR (300 MHz, TMS, CDCl3) d 1.89 (3H, s, CH3), 3.29 (3H, s, NCH3), 7.20±7.23 (2H, m, Ar), 7.36±7.47 ppm (3H, m, Ar). 13 C NMR (75 MHz, CDCl3) d 22.4, 37.2, 127.1, 127.7, 129.7, 144.7, 170.5 ppm (C=O). MS (EI) m/z 149 (M‡). HRMS calc. for C9H11NO: requires M, 149.0841; found: 149.0808 (M‡).

N-[4-(4-Dimethylaminobenzyl)phenyl]-N-methylacetamide 3. A blue solid; m.p. 104±106 8C. IR (CHCl3) n 1653 cm 1 (C=O). 1 H NMR (300 MHz, TMS, CDCl3) d 1.86 (3H, s, CH3), 2.92 (6H, s, NCH3), 3.23 (3H, s, NCH3), 3.90 (2H, s, CH2), 6.70 (2H, d, J ˆ 8:4 Hz, Ar), 7.07 (4H, d, J ˆ 7:5 Hz, Ar), 7.21 ppm (2H, d, J ˆ 8:4 Hz, Ar). MS (EI) m/z 282 (M‡). HRMS calc. for C18H22N2O requires M, 282.1732; found: 282.1750 (M‡). N,N,N0 ,N0 -Tetramethyl-4,40 -methylenedianiline 4. A blue solid; m.p. 89±91 8C. 1 H NMR (300 MHz, TMS, CDCl3) d 2.91 (12H, s, NCH3), 3.82 (2H, s, CH2), 6.71 (4H, d, J ˆ 8:6 Hz, Ar), 7.08 ppm (4H, d, J ˆ 8:6 Hz, Ar). 13 C NMR (75 MHz, CDCl3): d 39.9, 41.0, 113.2, 129.4, 130.5, 149.0 ppm. MS (EI) m/z 254 (M‡). HRMS calc. for C17H22N2 requires M, 254.1783; found: 254.1742 (M‡). N-{4-[4-(Acetylmethylamino)benzyl]phenyl}-N-methylacetamide 5. A blue solid; m.p. 96±98 8C. IR (CHCl3) n 1654 cm 1 (C=O). 1 H NMR (300 MHz, TMS, CDCl3) d 1.82 (6H, s, CH3), 3.25 (6H, s, NCH3), 3.97 (2H, s, CH2), 7.07 (4H, d, J ˆ 8:2 Hz, Ar), 7.19 ppm (4H, d, J ˆ 8:2 Hz, Ar). MS (EI) m/z 310 (M‡). HRMS calc. for C19H22N2O2 requires M, 310.1681; found: 310.1708 (M‡). N-[4-(4-Dimethylaminobenzyl)phenyl]acetamide 6. A blue solid; m.p. 96±98 8C. IR (CHCl3) n 1656 cm 1 (C=O). 1 H NMR (300 MHz, TMS, CDCl3): d 1.87 (3H, s, CH3), 3.25 (3H, s, NCH3), 3.31 (3H, s, NCH3), 4.01 (2H, s, CH2), 7.12 (4H, d, J ˆ 8:3 Hz, Ar), 7.22±7.27 (4H, m, Ar), 8.46 ppm (1H, s, NH). MS (EI) m/z 268 (M‡). HRMS calc. for C17H20N2O requires M, 268.1576; found: 268.1534 (M‡). 3.4. Friedel±Crafts reaction of N,N-dimethylaniline with ethyl glyoxylate To N,N-dimethylaniline (0.5 mmol, 60 mg, 0.05 ml) in Schlenk tube was added Yb(C8F17SO3)3 (9 mg, 0.005 mmol) and ethyl glyoxylate (255 mg, 2.5 mmol) and the reaction mixture was stirred at the RT for 24 h. The reaction solution was washed with water (10 ml  2) and extracted with dichloromethane (CH2Cl2). The solvent was removed under reduced pressure and the residue was puri®ed by a silica gel column chromatongraph (eluent: petroleum ether/EtOAc ˆ 5/1) to give the products 7±9. (4-Dimethylaminophenyl)hydroxyacetic acid ethyl ester 7. A colorless liquid. 1 H NMR (300 MHz, TMS, CDCl3) d 1.24 (3H, t, J ˆ 7:1 Hz, CH3), 2.95 (6H, s, NCH3), 3.26 (1H, d, J ˆ 6:0 Hz, OH), 4.18±4.12 (1H, m, CH2), 4.30±4.24(1H, m, CH2), 5.07 (1H, d, J ˆ 5:7 Hz, CH), 6.71 (2H, d, J ˆ 8:8 Hz, Ar), 7.26 ppm (2H, d, J ˆ 8:8 Hz, Ar). MS (EI) m/z 223 (M‡). HRMS calc. for C12H17NO3 requires M, 223.1208; found: 223.1212 (M‡). Bis-(4-dimethylaminophenyl)acetic acid ethyl ester 8. A colorless liquid. 1 H NMR (300 MHz, TMS, CDCl3) d 1.24 (3H, t, J ˆ 7:1 Hz, CH3), 2.91 (12H, s, NCH3), 4.17 (2H, d, J ˆ 7:1 Hz, CH2), 4.83 (1H, s, CH), 6.68 (4H, d, J ˆ 8:8 Hz, Ar), 7.17 ppm (4H, d, J ˆ 8:8 Hz, Ar). MS

M. Shi, S.-C. Cui / Journal of Fluorine Chemistry 116 (2002) 143±147

(EI) m/z 326 (M‡). HRMS calc. for C20H26N2O2 requires M, 326.1994; found: 326.2018 (M‡). Bis-(4-dimethylaminophenyl)acetic acid 9. A colorless liquid. 1 H NMR (300 MHz, TMS, CDCl3) d 2.91 (12H, s, NCH3), 4.85 (1H, s, CH), 6.28 (1H, s, OH), 6.69 (4H, d, J ˆ 8:8 Hz, Ar), 7.18 ppm (4H, d, J ˆ 8:8 Hz, Ar). MS (EI) m/z 298 (M‡). HRMS calc. for C18H22N2O2 requires M, 298.1681; found: 298.1632 (M‡). Acknowledgements

[3] [4] [5] [6] [7]

We thank the State Key Project of Basic Research (project 973) (no. G2000048007) and the National Natural Science Foundation of China (20025206) for ®nancial support. We also thank the Inoue Photochirogenesis Project (ERATO, JST) for chemical reagents. References [1] G.A. Olah, Friedel±Crafts and Related Reaction, Vol. III, Part I, Interscience, New York, 1964. [2] (a) S. Kobayashi, I. Hachiya, T. Takahori, M. Araki, M. Ishitani, Tetrahedron Lett. 33 (1992) 6815±6818; (b) S. Kobayashi, H. Ishitani, I. Hachiya, M. Araki, Tetrahedron 50 (1994) 11623±11636; (c) S. Kobayashi, S. Wakabayashi, S. Nagayama, H. Oyamada, Tetrahedron Lett. 38 (1997) 4559±4562;

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