Fluorine-Containing Synthons - American Chemical Society

Chapter 20

Fluorinated Synthon: Asymmetric Catalytic Reactions

Downloaded by PURDUE UNIV on August 30, 2016 | http://pubs.acs.org Publication Date: July 21, 2005 | doi: 10.1021/bk-2005-0911.ch020

Koichi Mikami, Yoshimitsu Itoh, and Masahiro Yamanaka Department of Applied Chemistry, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8552, Japan

1. Introduction Organofluorine compounds continue to attract much attention, having important applications as physiologically active agents, liquid crystals, and in other areas ( 1 ). Frequently, mono-fluoro- or trifluoromethyl-containing compounds having specific absolute configuration are synthesized to produce new analogues that exhibit particularly high physiological activity and remarkable physical properties ( 2). Methods for the synthesis of fluorine-containing compounds can be broadly classified into two types: carbon-fluorine bond forming reactions (fluorination with fluorinating reagents)(1 a,b,c, 3) and carbon-carbon bond forming reactions employing fluorinated synthons, such as perfluoro-alkanes and -alkenes or fluorine-containing carbonyl compounds. In this article, we summarize our research on catalytic asymmetric syntheses using fluorinated synthons such as fluoral and trifluoropyruvate. Formally, the reaction involves electrophilic replacement of a C-H bond of an olefin, silyl enolether or aromatic compound with a C-C bond appended with a trifluoromethyl group. (Figure 1). 2. Catalytic enantioselective C-C bond formation of fluorinated carbonyl compounds Catalytic enantioselective carbon-carbon bond forming reactions with prochiral fluorinated carbonyl compounds represent very efficient and economical approaches to chiral organo-fluorine compounds. Therefore, there is much current interest in developing procedures for asymmetric catalytic carboncarbon bond forming reactions involvingfluorinatedsynthons.

356

© 2005 American Chemical Society

Soloshonok; Fluorine-Containing Synthons ACS Symposium Series; American Chemical Society: Washington, DC, 2005.

357


2-1.

Carbonyl-ene reaction

C-H Bond activation and C-C bond formation are the clues to synthetic exploitation in organic synthesis. In principle, the ene reaction converts readily available alkenes into more functionalized products with activation of an allylic C-H single bond and transposition of the C=C double bond ( 4 ). This intermolecular [l,5]-hydrogen shift is one of the simplest atom-economical and green processes available for C-C bond formation ( 5). In particular, the class of the ene reactions involving carbonyl compound as the enophile is referred to as the 'carbonyl-ene reaction' (6). When carbonyl compounds are used as enophiles, alcohols are exclusively formed in a stereoselective manner. In the carbonyl-ene reaction with fluoral, binaphthol (BINOL)-derived titanium (BINOLate-Ti) catalyst (obtained from BINOL and TiCUiO'Pr^) in the presence of MS4A gave the ene product 1 and the Friedel-Crafts product 2 (Table 1) ( 7). The ratio of 1 and 2 was higher for fluoral than for chloral. Table 1. BINOLate-Ti catalyzed carbonyl-ene vs. Friedel-Crafts reactions of fluoral and chloral. loH + TiCI (0'Pr)2 (io mol%) 2

OH (10

c?

moI%)

η

X

0

F

1 0 1

Cl

OH

MS4A

χ

Η CX CH CI (JOeol o°C, 30min 3

2

% yield

2

V f ^ ^ C X a X ^ ^ C X a 1

1

OH

2

ratio (% ee) 2

78

62 (>95% ee)

93

76 (>95% ee)

38 (>95% ee) 24 (>95% ee)

57

55 (26% ee)

45 (75% ee)

49

52 (34% ee)

48 (66% ee)

This difference can be explained based on the balance of the LUMO energy level of the aldehyde and the charge distribution on the carbonyl carbon. We calculated the charge and LUMO energy in the complex between the aldehyde and acid H* used as the chemical model of the Lewis acid at the RHF/6-31G* level. These calculation show that the LUMO energy is lower forfluoralthan for chloral, and thus the positive charge on the carbonyl carbon is higher with chloral (Figure 2). Thefrontierorbital interaction between the ene HOMO and enophile LUMO is the principal interaction in the ene reaction. Consequently, fluoral, having the lower LUMO energy, could show a greater tendency for concerted ene reaction. In contrast, chloral, having larger partial positive charge at the carbonyl carbon, more readily undergoes stepwise cationic reactions, in this case the Friedel-Crafts (F-C) reaction (Scheme 1) ( 8).


358

Fluorinated Synthon

FC Downloaded by PURDUE UNIV on August 30, 2016 | http://pubs.acs.org Publication Date: July 21, 2005 | doi: 10.1021/bk-2005-0911.ch020

3

ι

OH

H III OH

Ene Reaction O

OH

F C^H 3

5/0

Aldol Reaction

SD

OH

OH F C^C0 R 3

2

Friedel-Crafts Reaction Figure L Catalytic asymmetric reaction usingfluorinatedsynthons

X=F X = Cl

LU MO (eV) -5.40 -4.88

Charge of carbonyl carbon +0.61 +0.64

Figure 2. LUMO energy levels and charge distributions of carbonyl carbon of fluoral and chloral (RHF/6-31G**)


359

Scheme 1

χ

(Concerted)

H ^ C X

3

I f

s t e

P

w i s e

)

^H.._,-TiLn*

^cx


Q^ex

3

Q^cx

3

3

By introducing an electron donating methyl group on the ene components to increase the HOMO level, the ene reaction was facilitated and the F-C reaction was retarded (Scheme 2) ( 9). In regard to the diastereoselectivity of the ene reaction, the syn product is obtained with nearly perfect selectivity. This selectivity can be explained by considering the 6-membered ring transition state ( 1 0) as indicated in Scheme 2. The syn isomer is preferentially produced due to destabilization by 1,3-diaxial interactions in the transition state that produces the anti isomer.

Scheme 2

ο H ^ C F ( 2 . 0 eq.) (fl)-BINOL-Ti (10 mot%) 3

MS4A, C H C I 0 "C, 30 min 2

OH CF

2

3

anti

syn

ratio ι • ee) n=1 2

syn % yield 98 (96% ee) 94 94(95%ee) 76

anti 2 6

Hemiacetals of such aldehydes can also be employed in these carbon-carbon bond-forming reactions. In the reaction using difluoroacetaldehyde ethyl hemiacetal, MS5A rather than MS4A can be used in order to preferentially trap ethanol generated from the difluoro acetal. This leads to a higher ene selectivity along with high enantioselectivity (> 95% ee) (Table 2) ( 1 1).


360 Table 2. BINOLate-Ti catalyzed carbonyl-ene reaction of hemiacetal. OH EtO^CHF (1.2 eq.) 2

(K)-B!NOL-Ti (10mol%)

Π

0°C, CH C! , 2h

V V "

2

2


additive % yield

-

23

MS4A

30

MS5A

47

—

, Ci x

χ +CL χ

^v^CHF ^r'^CHF2 • syn - anti ratio(% ee) syn anti X

2

ee) : 10 ee) : 7 (>95% ee) 91 (>95% ee) : 9 90 (>95%

93 (>95%

We recognized that a carbonyl-ene reaction with CF-ketones would be a synthetically important process, providing a short route to chiral tertiary a-CF carbinols with homo-allylic functionality. However, there had been essentially no successful examples of asymmetric catalysis of ketone-ene reactions (12), because of low ene reactivity of ketones compared to aldehydes. Recently we reported the first successful example of asymmetric catalysis of the trifluoromethylpyruvate-ene reaction using the "naked" dicationic SEGPHOSPd(II) complex in CH C1 , derivedfromSEGPHOS [(4,4'-bi-l,3-benzodioxole)5,5'-diyibis(diarylphosphine)] ( 1 3), PdCl (CH CN) , and AgSbF , to construct the corresponding quaternary carbon center (14). The presence of the cationic SEGPHOS-Pd(II) complex (3) leads to a high chemical yield, (£)-olefin selectivity, awtf-diastereoselectivity, along with high enantioselectivity in this much less reactive carbonyl-ene reactions with ketones, even with less reactive mono- and 1,2-disubstituted olefins (Scheme 3) ( 1 5). 3

3

2

2

2

3

2

6

2-2. Aldol reaction

The Mukaiyama-aldol reaction of silyl enol ethers is one of the most important carbon-carbon bond forming reactions in organic synthesis (16). Withfluoral,this aldol reaction can readily proceed even in the absence of a catalyst, presumably due to the high electrophilicity of fluoral and an intermolecular interaction between Si and F (Scheme 4) ( 1 1). However, it is possible to suppress the uncatalyzed reaction process and achieve a catalytic asymmetric reaction simply by adding ketene silyl acetal (KSA) and fluoral simultaneously to a solvent containing the BINOLate-Ti catalyst, (Scheme 5). Using this simple procedure, a high level of enantioselectivity was achieved (up to 96% ee of the (/?)-enantiomer).



361

Scheme 4

HCI

SIMS3

°' i R S ^

9 + X Η

^ίΗ CF

Toluene -78 C

3

0

0 H

π

τ

R S ^ ^ X F ,

e

R^Bu, 50% Ph, 66%

Scheme 5 OTMS R S ^ (R)-BINOL-Ti (20 mol%)

Ο

HQ

V '

to|uene

o°c

9

OH

RS^V^CFa

X Η

CF

3

R^Bu, 56% yield, 90% ee Ph, 38% yield, 96% ee


362

In addition, with a ketene silyl thioacetal having a methyl group at the a-position, the reaction proceeded with high enantioselectivity, despite having low diastereoselectivity (Scheme 6).

Scheme 6 OTMS EtS (fWINOL-Tl (20 md%)

> o '

toluene

o°c

H^CF % yield 64 48


3

KSA 95%Z 98%E

syn : anti 48 (55% ee) : 52 (64% ee) 44 (89% ee) : 56 (83% ee)

2-3. Friedel-Crafts reaction Friedel-Crafts (F-C) reactions also constitute one of the most useful carbon-carbon bond-formation processes in organic synthesis ( 1 7). However, there have been only very few reports of asymmetric catalytic F-C reactions. Recently, we investigated the asymmetric catalytic F-C reactions of the prochiral fluorine-containing carbonyl compounds leading to the chiral tertiary a-CF carbinols. We reported the asymmetric catalytic F-C reaction of silyl enol ethers under the Mukaiyama-aldol reaction conditions. The reaction of tertbutyldimethylsilyl or triisopropylsilyl enol ether with fluoral was carried out using the (#)-BINOLate-Ti complex to afford the F-C product 4 with high % ee rather than the usual aldol product 5 (Table 3) ( 1 8). 3

The ratio of the F-C product depends very much on the bulkiness of the silyl group. Indeed, triisopropylsilyl enol ether overwhelmingly afforded 4 in contrast to trimethylsilyl enol ether, which gave 5 instead of 4. The Mukaiyama aldol reaction, namely Lewis acid-promoted carbonyl addition reaction of a silyl enol ether to aldehydes or ketones, is known to proceed via the desilylated β metaloxy carbonyl chelate intermediates. However, the silyl enol ether F-C product can also be generated under Lewis acid-catalyzed Mukaiyama aldol conditions. This results from the ability of the bulky silyl group to inhibit the nucleophilic substitution reaction on the silyl group (path a in Figure 3). This allows the deprotonation reaction pathway to proceed to produce a silylenol ether (path b in Figure 3). Furthermore, the strong electron-withdrawing C F group could lower the nucleophilicity of the titanium alkoxide in the zwitterionic intermediate to further retard the reaction path a. 3

Adding value to this FC reaction is the fact that subsequent diastereoselective reactions of the silyl enol ether F-C product with electrophiles can yield highly functionalized fluorinated aldols that are of material and pharmaceutical interests.


363


Table 3. Asymmetric Friedel-Crafts reactions of siiyl enoi ethers with flu oral RaSiO

R SJO

0

C F a

Λ

OH

3

Ο

Ta%y/e/d

R^H 5

4

2

R

cat (mot %)4(£:ZJ 0

OH

5 27*

%ee 0

TMS

4'-Me-Ph

Me

20

TBDMS

Ph

H

5

67(1:5)

14

98

TIPS

Ph

H

1

90(1:5)

4

96

e

the TMS ether. The diastereomeric ratio=1:4.

ai do!

Friedel-Crafts

Figure 3. Comparison ofaldol pathway (path a) and Friedel-Crafts pathway (path b) in the zwitterionic intermediate.


364 In addition, the oxidation by m-CPBA or desilylation by TBAF of 4 leads selectively to mono-protected syn-diol 6 and anti-sàdol 7 with high diastereoselectivity, respectively (Scheme 7).

Scheme 7 m-CPBA MeOH, r.t. (X = Me) TBDMSO' HSO

OH

TBDMSQ Ar

CF,

CF

Ο TBAF T H F - H 0 , r.t. (X = OMe)

Ar=4'-X-Ph


OH

Λ

Λ

2

4

3

'66 ((95% de)

CF

3

7 (92% de)

We also studied the asymmetric F-C reaction of a vinyl ether with fluoral catalyzed by (φ-BINOLate-Ti complex derived from BINOL and TiCl (0 Pr) . In a similar manner to the F-C reaction of silyl enol ether, a reactive vinyl ether was obtained as the F-C product. This can sequentially react with m-CPBA to afford highly functionalized organofluorine compounds. The reaction with the enol ether gave the F-C product almost exclusively and with high enantioselectivity (up to 85% ee), with essentially no aldol product being obtained (Table 4). When employing a vinyl ether possessing a ^-methyl substituent, (£)-8 was predominantly obtained irrespective of the geometry of the substrate. The subsequent diastereoselective oxidation of the F-C products by mCPBA provided diastereoselectively «sy«-a,p-dihydroxy ketones 9 in high chemical yields (Scheme 8) ( 1 9) ,

2

2

Table 4. Asymmetric Friedel-Crafts reactions of vinyl ether with fluoral M e C

p

O

MeO

OH

R

R

cat

Ph

Me

10mol %

54% (1:2)

72

4'-Me-Ph

Η

20mol %

64% (5:1)

85

1

%ee

8(E:Z)

Scheme 8 MeO A r A

r

OH

Ο

AAcF, Τ

c p

3

Ar = 4'-Me-Ph

m>CPBA, p - T s O H . MeOH, r.t. MeOH-H 0 reflux

A

OH

A A

r

2

H

O

c

C F

p

3

'

9 80% (>95% de)


365

We also investigated the asymmetric F-C reation of fluoral with aromatic substrates. Aromatic compounds have low nucleophilicity relative to silyl enol ethers or vinyl ethers, and hence the asymmetric F-C reaction needs Lewis acidic metal catalyst such as BINOLate-Ti. Both the yield and the enantioselectivity of the F-C product are increased when a catalyst with high Lewis acidity is used and an electron-withdrawing group (Br) is introduced onto BINOL. The asymmetric F-C reaction of phenyl ethers selectively gave p-10 rather than o-lO. The regioselectivity of the F-C product was increased by using w-butyl phenyl ether (p-10: o-10 = 8:1) (2 0). When (#)-6,6'-Br BINOL is added as an additive (), the yield and enantioselectivity are further increased (89% yield, 90% ee), and an asymmetric activation effect is observed (Table 5) (2 1,2 2). Downloaded by PURDUE UNIV on August 30, 2016 | http://pubs.acs.org Publication Date: July 21, 2005 | doi: 10.1021/bk-2005-0911.ch020

r

Table 5. Asymmetric Friedel-Crafts reactions of aromatic compounds with fluoral HQ H (K)-BINQL-Ti ^cf3

R cat. (mol %) Me Me

n-Bu Ph Me n-Bu

30 5 15 10 10 10

CH2CI2 0 °C

RO

a

additive (mol %) %p-10:o-10 yield %ee

( Κ ) - 6 , 6 · - Β Γ - Β Ι Ν Ο Ι . (10) (R)-6,6'-Br BINOL (10) 2

r

82 94 85 90 89 90

4:1 4:1 8:1 3:1 4:1 8:1

73 84 83 54 90 90

^he enantiomeric excess of p-10.

Recently, we developed an asymmetric F-C reaction of ethyl trifluoropyruvate with aromatic compounds catalyzed by Pd(II) BINAP or SEGPHOS complexes. This reaction can proceed at lower reaction temperature (-30 °C) than the reaction with fluoral and gives products with high enantioselectivity (2 3). The F-C product obtained using the Pd(II) catalyst gave higher chemical yield and enantioselectivity than that using a Cu(II) catalyst (2 4). In marked contrast to the carbonyl-ene reaction, the BINAP ligand provides higher enantioselectivity than does the SEGPHOS ligand (Scheme 9).

References 1

a) Mikami, K.; Itoh, Y.; Yamanaka, M. Chem. Rev. 2004, 104, 1-16. b) Mikami, K.; Itoh, Y.; Yamanaka, M. Fine Chemical 2003, 32(1), c) Mikami, K.; Itoh, Y.; Yamanaka, M. Fine Chemical 2003, 32(2), 11-20. d) Hiyama, T.; Kanie, K.; Kusumoto, T.; Morizawa, Y.; Shimizu, M. OrganofluorineCompounds;Springer-Verlag: Berlin Heidelberg, e) Soloshonok, V. A. Ed. Enantiocontrolled Synthesis of Fluoro-

35-50.

2000.


366


Scheme 9

2 3

4

5 6 7 8 9

OrganicCompounds; Wiley: Chichester, 1999. f) Chambers, R. D. Ed. Organofluorine Chemistry, Springer, Berlin 1997. g) Iseki, K. Tetrahedron 1998, 54, 13887-13914. h) Ojima, I.; McCarthy, J. R.; Welch, J. T. Eds. Biomedical Frontiers of Fluorine Chemistry; American Chemical Society: Washington DC, 1996. i) Smart, Β. E., Ed. Chem Rev. 1996, 96, No. 5 (Thematic issue offluorinechemistry).j) Banks, R. E.; Smart, Β. E.; Tatlow, J. C. Eds. Organofluorine Chemistry: Principles and Commercial Applications; Plenum Press: New York. 1994. k) Kitazume, T.; Ishihara, T.; Taguchi, T. Chemistry of Fluorine; Koudansha: Tokyo, 1993. l) Ishikawa, N. Ed. Synthesis and Reactivity of Fluorocompounds; CMC: Tokyo, Vol. 3, 1987. m) Ishikawa, N.; Kobayashi, Y. Fluorine Compounds; Koudansha: Tokyo, 1979. n) Hudlicky, M. Chemistry of Organic Fluorine Compounds, 2nd edn; Ellis Horwood: Chichester, 1976. a) Smart, Β. E. J. Fluorine Chem. 2001, 109, 3-11. b) Schlosser, M . Angew. Chem. Int. Ed. 1998, 37, 1496-1513. For asymmetric fluorination, see: a) Togni, A. Chem. Rev. in press. b) Gouverneur, V.; Greedy, B. Chem. Eur. J. 2002, 8, 767-771. c) Muñiz, K. Angew. Chem. Int. Ed. 2001, 40, 1653-1656. d) Resnati, G. Tetrahedron 1993, 49, 9385-9445. e) Bravo, P.; Resnati, G. Tetrahedron: Asymmetry 1990, 1, 661-692. Comprehensive reviews on ene reactions: a) Mikami, K.; Shimizu, M.; Chem. Rev. 1992, 92, 1021-1050. b) Snider, Β. B. In Comprehensive Organic Synthesis; Trost, Β. M.; Fleming, I. Eds., Pergamon: London, 1991; Vol 2, p 527-561 and Vol 5, p 1-27. a) Trost, Β. M. Science 1991, 254, 1471-1477. b) Trost, Β. M. Angew. Chem. Int. Ed. Engl. 1995, 34, 259-281. Review on 'carbonyl-ene reactions': Mikami, K.; Terada, M.; Shimizu, M.; Nakai, T. J. Synth. Org. Chem. Jpn. 1990, 48, 292-303. Milkami, K.; Yajima, T.; Terada, M.; Uchimaru, T. Tetrahedron Lett. 1993, 34, 7591-7594. Akihiro, I.; Mikami, K. J. Synth. Org. Chem. Jpn. 2000, 58, 324-333. Mikami, K.; Yajima, T.; Terada, M.; Kato, E.; Maruta, M. Tetrahedron: Asymmetry 1994, 5, 1087-1090.


367

1 0

1 1 1 2

a) Mikami, K.; Loh, T. -P.; Nakai, T. Tetrahedron Lett. 1988, 29, 63056308. b) Yamanaka, M.; Mikami, K. Helv. Chim. Acta 2002, 85, 42644271. Mikami, K.; Yajima, T.; Takasaki, T.; Matsukawa, S.; Terada, M.; Uchimaru, T.; Maruta, M. Tetrahedron 1996, 52, 85-98. Evans reported the excellent example of asymmetric catalysis of glyoxylate-ene reaction with a variety of olefins by chiral bis-oxazoline Cu complexes: Evans, D. Α.; Tregay, S. W.; Burgey, C. S.; Paras, Ν. Α.; Vojkovsky, T. J. Am. Chem. Soc. 2000, 122, 7936-7943. SEGPHOS = (4,4'-bi-1,3-benzodioxole)-5,5'-diylbis(diphenylphosphine). a) Saito, T.; Yokozawa, T.; Ishizaki, T.; Moroi, T.; Sayo, N.; Miura, T.; Kumobayashi, H. Adv. Synth. Catal. 2001, 343, 264-267. EP 850945A 1998, US 5872273 1999. Reviews: a) Martin, S. F. Tetrahedron 1980, 36, 419-460. b) Fuji, K. Chem. Rev. 1993, 93, 2037-2066. c) Corey, E. J.; Guzman-Perez, A. Angew. Chem. Int. Ed. 1998, 37, 388-401. Aikawa, K.; Kainuma, S.; Hatano, M.; Mikami, K. Tetrahedron Lett. 2004, 1, 183-185. Reviews: a) Carreira, Ε. M. In Comprehensive Asymmetric Catalysis; Jacobsen, Ε. N.; Pfaltz, Α.; Yamamoto, H., Eds.; Springer: Berlin Heidelberg, 1999; Vol. 3, p 997-1065. b) Mekelburger, Η. B.; Wilcox, C. S. In Conprehensive Organic Synthesis; B. M. Trost, Β. M.; Fleming, I., Eds,; Pergamon press: Oxford, 1991; Vol 2, p 99-131. c) Heathcock, C. H. In Conprehensive Organic Synthesis; Β. M. Trost, Β. M.; Fleming, I., Eds,; Pergamon: Oxford, 1991; Vol 2, p 133-179 & 181-238. d) Kim, B. M.; Williams, S. F.; Masamune, S. In Conprehensive Organic Synthesis; Β. M. Trost, Β. M.; Fleming, I., Eds,; Pergamon: Oxford, 1991; Vol 2, p 239-275. e) Rathke, M. W.; Weipert, P. In Conprehensive Organic Synthesis; Β. M. Trost, Β. M.; Fleming, I., Eds,; Pergamon: Oxford, 1991; Vol 2, p 277-299. f) Paterson, I. In Comprehensive Organic Synthesis; B. M. Trost, Β. M.; Fleming, I., Eds,; Pergamon: Oxford, 1991; Vol 2, p 301319. g) Mukaiyama, T.; Org. React. 1982, 28, 203-331. 2+


1 3

1 4

1 5 1 6

1 7 Reviews: a) Smith, M . B. Organic Synthesis; McGraw-Hill: New York, 1994; p 1313-1349. b) Heaney, H. In Comprehensive Organic Synthesis; Trost, Β. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 2, p 733-752. c) Roberts, R. M.; Khalaf, A. A. In Friedel-Crafts Alkylation Chemistry. A Century ofDiscovery; Dekker: New York, 1984. d) Olah, G. A. Friedel-Crafts Chemistry; Wiley-Interscience: New York, 1973. 1 8 Ishii, Α.; Kojima, J.; Mikami, K. Org. Lett. 1999, 1, 2013-2016. 1 9 Ishii, Α.; Mikami, K. J. Fluorine. Chem. 1999, 97, 51-55. 2 0 Ishii, Α.; Soloshonok, V. Α.; Mikami, K. J. Org. Chem. 2000, 65, 15971599. 2 1 Review for asymmetric activation see: Mikami, K.; Terada, M.; Korenaga, T.; Matsumoto, Y.; Ueki, M.; Angelaud, R. Angew. Chem. Int. Ed. 2000, 39, 3532-3556. 2 2 Mikami, K.; Yamanaka, M. Chem. Rev. 2003, 103, 3369-3400. 2 3 Aikawa, K.; Mikami, K. in preparation 2 4 Zhuang, W.; Gathergood, N.; Hazell, R. G.;Jørgensen,K. A. J. Org. Chem. 2001, 66, 1009-1013.


Fluorine-Containing Synthons - American Chemical Society

Recommend Documents