Palladium-indium-indium(III) chloride-mediated allyl cross-coupling reactions using allyl acetates

Article abstract of DOI:10.1002/adsc.200404125

Allylindiums in situ generated by reductive transmetalation of π-allylpalladium(II) complexes, obtained from allyl acetates and palladium(0) catalyst, with indium and indium(III) chloride are effective nucleophilic cross-coupling partners in Pd-catalyzed allyl cross-coupling reactions with a variety of electrophilic cross-coupling partners.

Full text of DOI:10.1002/adsc.200404125

COMMUNICATIONS
Palladium-Indium-Indium(III) Chloride-Mediated Allyl
Cross-Coupling Reactions Using Allyl Acetates
Phil Ho Lee,* Dong Seomoon, Kooyeon Lee, Sundae Kim, Hyunseok Kim,
Hyun Kim, Eunkyong Shim, Miae Lee, Seokju Lee, Misook Kim,
Madabhushi Sridhar
Department of Chemistry, Kangwon National University, Chunchon 200-701, Republic of Korea
Fax: (þ82)-33-253-7582; e-mail: phlee@kangwon.ac.kr
Received: May 1, 2005; Accepted: October 1, 2004
Abstract: Allylindiums in situ generated by reductive
transmetalation of p-allylpalladium(II) complexes,
obtained from allyl acetates and palladium(0) cata-
lyst, with indium and indium(III) chloride are effec-
tive nucleophilic cross-coupling partners in Pd-cata-
lyzed allyl cross-coupling reactions with a variety of
electrophilic cross-coupling partners.
ladiums(II) complexes has been studied and then
many successful examples of the Pd-In-mediated allyla-
[
8]
[9]
[10]
tion of aldehydes, imines, and oximes were report-
ed. In connection with our current research interest in
[11]
the synthetic utility of organoindium reagents,
we
have reported Pd-catalyzed cross-coupling reactions of
in situ generated allylindiums from allyl halides and in-
dium with a variety of electrophilic coupling part-
[
5 g, h]
Keywords: allyl acetate; allylation; cross-coupling; in-
ners.
Our continuing efforts in the area of organoin-
dium; palladium
dium chemistry led us to find that allyl acetates, which
are easily derived from available allyl alcohols, can be
effectively utilized in the Pd-catalyzed allyl cross-cou-
pling reaction, via p-allylpalladium(II) complexes and
their transmetalation with In-InCl , in the presence of
3
The widespread natural occurrence and potential for a catalytic amount of Pd(Ph P) (Scheme 1).
3
4
further functionalization of allylaromatic compounds
have promoted a continued interest in synthetic meth-
ods for the introduction of allyl groups onto the aromatic
[
1]
[2]
nucleus. Friedel–Crafts alkylation, Claisen rear-
[3]
rangement, substitution reactions of allyl halides
with various aromatic organometallic reagents, and Scheme 1.
[
4]
the transition metal-mediated cross-couplings represent
[
5]
the most powerful allylation methods. Among these,
the Pd-catalyzed cross-coupling reaction has attracted
We first investigated various experimental conditions
much attention in the area of allylation methods. One in the model reaction using 4-n-butyliodobenzene (1)
of the most frequently used methods for allyl cross-cou- with allyl acetate (2) (Table 1). Of the solvents tested
pling reactions involves the use of allylstannanes as cou- (DMF, THF, CH CN, and THF-H O), DMF was opti-
3
2
pling partners, which has attracted much attention as a mum. Among the catalysts examined, Pd(Ph P) was
3
4
result of their availability, air- and moisture-stability, the most suitable in terms of the yields. Other palladium
and their compatibility with a variety of functional complexes, such as PdCl , Pd(OAc) , Pd(CH CN) Cl ,
2
2
3
2
2
[6]
groups. Although allylstannanes are generally accessi- Pd(PhCN) Cl , and Pd dba CHCl in the presence of
2
2
2
3
3
ble, such procedures are sometimes inadequate as the Ph P produced 4-allyl-n-butylbenzene (3) in good
3
requisite allylmetals are difficult to obtain. The direct yields. The combination of In and InCl as a reductive
3
conversion of readily available allylic substrates to allyl- transmetalating agent for p-allylpalladiums(II) com-
metal species is desirable. Generally, the allylating re- plexes gave the allyl cross-coupling product in good
[
8j]
agents have been limited to allyl halides, particularly all- yield. However, the desired product was obtained in
[
8c]
yl bromides and iodides. Allyl chloride has been used only 30% yield with InI (entry 13). Also, the reaction
with an iodide salt via in situ generated allyl iodide. was found to proceed efficiently in the presence of LiCl
[
5g]
Therefore, overcoming these shortcomings is a prereq- as an additive (entries 6, 9 and 10). A tertiary alkyla-
uisite for developing new allylmetals as coupling part- mine was necessary toreduce side products such as n-bu-
ners. Recently, a new method for the preparation of allyl- tylbenzene and 4,4’-di-(n-butyl)-1,1’-biphenyl. Of the
[
7]
indiums via a reductive transmetalation of p-allylpal- amines tested, N,N-dimethyl-n-butylamine gave the
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DOI: 10.1002/adsc.200404125
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Phil Ho Lee et al.
Table 1. Optimization of Pd-In-mediated cross-coupling re- mean that electron density on the aromatic ring does
action of 4-n-butyliodobenzene with allyl acetate.
not seriously effect the efficiency of the reactions. Aryl
iodides are more reactive than aryl bromides and give
a higher yield of the cross-coupling product (entries 1
and 2). However, the triflate of 1-naphthol afforded 1-
allylnaphthalene (4) in 33% yield under optimized con-
ditions (entry 3). It should be noted that the present con-
ditions could be applied to carbonyl-bearing aryl iodides
(
entries 12–17). Vinyl triflates worked equally well with
in situ generated allylindium from allyl acetate, produc-
ing the allylic compound 21 in 84% yield (entry 19). a-
Bromostyrene was treated with allyl acetate to give a
59% yield of 2-phenyl-1,4-pentadiene (22) and a 7%
yield of trans-1-phenyl-1,4-pentadiene (23) (entry 20).
For allyl acetates as coupling partners, the presence of
a methyl substituent at the a, b or g position affected
both reaction rates and product yields. The use of allyl
acetate and 2-methylallyl acetate in the allyl cross-cou-
pling reaction gave the corresponding allylic com-
pounds in good yields. Reaction of 1-iodonaphthalene
Reactions performed in the presence of 10 mol % with allyl acetate gave the allyl cross-coupling product
Pd(PPh ) , 2.0 equivs. of In, 0.5 equivs. of InX , 3.0 equivs. (4) in 81% yield under the optimized conditions (en-
[
a]
3
4
3
of LiX, and 2.0 equivs. of base, unless otherwise noted.
Numbers in parenthesis indicate the recovered yield of
-n-butyliodobenzene.
GC yield.
mol % Pd(PPh ) was used.
Indium metal was not used.
trans-1,3-Bis(4-n-butylphenyl)propene.
.0 equiv. of K CO was used.
try 2). 1-Iodonaphthalene was treated with 2-methylall-
yl acetate to produce 7in 74% yield (entry 6). Subjecting
4
1-iodonaphthalene to the allylindium derived from the
[
[
[
[
[
b]
c]
d]
e]
f]
corresponding acetate of 3-buten-2-ol afforded the de-
sired products 5 and 6 in 57% yield, but the product 5 re-
sulting from a-attack predominated (a:g¼3.7:1) (en-
try 4). Although reaction of 1-iodonaphthalene with
crotyl acetate gave the allyl cross-coupling products (5
and 6) in 46% yield, the regioselectivity of this reaction
5
3
4
1
2 3
was similar to that of 1-methyl-2-propenyl acetate to
[
12]
[5 g, h]
best result (entries 4, 6, and 14). Inorganic bases re- provide 5 as the major compound (entry 5).
sulted in low yields (entry 11). Of the reaction condi-
tions examined, the best results were obtained with not been established, a possible reaction mechanism
0 mol % Pd(Ph P) , 2.0 equivs. of In, 0.5 equivs. of for the Pd-In-mediated allyl cross-coupling reaction of
Although the mechanism of the present reaction has
1
3
4
InCl , 3.0 equivs. of LiCl and 2 equivs. of N,N-dimeth- aryl iodides with allyl acetate is shown in Scheme 2.
3
yl-n-butylamine in DMFat 1008C for 9 h, which provid- The initially formed p-allylpalladium(II) complex un-
ed 4-allyl-n-butylbenzene (3) in 65% yield (entry 14). dergoes reductive transmetallation by In and InCl to
3
The use of allyl chloride, allyl alcohol, and acrolein di- give the allylindium(III) species, which subsequently
ethyl acetal instead of allyl acetate in the Pd-In-mediat- undergoes cross-coupling with the aryl iodide in the
ed allyl cross-coupling reactions produced the desired presence of Pd(0) catalyst to yield allylarenes. The pres-
compound 3 in 32%, 5% and 0% yields, respectively.
ent reaction is one of the good examples in which the
As shown in Table 2, this newcatalytic protocolfor the Pd(0) catalyst is simultaneously involved to two catalyt-
Pd-mediated allyl cross-coupling reactions of aryl hal- ic cycles in a one-pot reaction (Scheme 2).
ides with in situ generated allylindiums from allyl ace-
In conclusion, in situ generated allylindiums derived
tates in the presence of Pd-In-InCl could be applied from the reductive transmetalation of p-allylpalladi-
3
to a broad range of substrates, and it was found that a di- um(II) complexes, obtained from a variety of allyl ace-
verse range of functional groups were compatible with tates and a Pd(0) catalyst, with In and InCl are effective
3
the reaction conditions. For example, aryl iodides bear- nucleophilic cross-coupling partners in Pd-catalyzed
ing n-butyl (entry 7) and methoxy (entries 8–10) as cross-coupling reactions. A variety of electrophilic
electron-donating groups and trifluoromethyl (en- cross-coupling partners such as aryl iodides, vinyl bro-
try 11), acetyl (entry 12), ethoxycarbonyl (entries 13– mide and triflates participate in this reaction. The pres-
1
7), and nitro (entry 18) as electron-withdrawing groups ent method complements existing synthetic methods as
smoothly reacted with allyl acetate in the presence of a result of advantageous features such as the ready avail-
Pd(0)-In-InCl to give the corresponding allylaromatic ability of allyl acetates, the high reaction efficiency and
3
compounds in moderate to good yields. These results operational simplicity.
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Palladium-Indium-Indium(III) Chloride-Mediated Allyl Cross-Coupling
COMMUNICATIONS
Table 2. Pd-In-mediated allyl cross-coupling reactions of electrophilic coupling partners with allyl acetates.
[
a]
Reactions performed in the presence of 10 mol % Pd(PPh ) , 2.0 equivs. of In, 0.5 equivs. of InCl , 3.0 equivs. of LiCl, and
3
4
3
2
al.
used.
2
.0 equivs. of n-BuNMe , unless otherwise noted. Numbers in parenthesis indicate recovered yield of starting materi-
2
[
b]
[c]
[d]
[e]
[f]
GC yield. Ratio of 5 to 6¼3.7: 1.
Ratio of 5 to 6¼2.3: 1. Et Nwas used.
5 mol % Pd(PPh3)4 was
4,4’-Bis(2-hydroxy-4-penten-2-yl)-1,1’-biphenyl. Ratio of 15 to 16¼
3
[
g]
[h]
[i]
2-(4-Allylphenyl)-4-penten-2-ol.
[
j]
[k]
[l]
.9: 1. n-BuNMe was not used.
Base was not used. Reaction proceeded at 258C. Ratio of 22 to 23¼8.4: 1.
2
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COMMUNICATIONS
Phil Ho Lee et al.
York, 1975; b) E. Wenkert, J. B. Fernandes, E. L. Michel-
otti, C. S. Swindell, Synthesis 1983, 701.
[
2] a) C. Friedel, J. M. Crafts, Bull. Soc. Chim. Fr. 1877, 27,
5
30; b) C. C. Price, Org. React. 1946, 3, 1; c) G. A.
Olah, Friedel–Crafts and Related Reactions, Vols. 1–4,
Wiley-Interscience, New York, London, Sydney, 1963;
d) R. Koncos, B. S. Friedman, Friedel–Crafts and Related
Reactions, Vol. 1, Part II (Ed.: G. A. Olah), Wiley, New
York, 1964, pp. 289; e) G. A. Olah, Friedel–Crafts Chem-
istry, Wiley, New York, 1973; f) R. M. Roberts, A. A.
Khalaf, Friedel–Crafts Alkylation Chemistry, Marcel
Dekker, New York, 1984; g) G. A. Olah, R. Krishnamur-
ti, G. K. S. Prakash, Comprehensive OrganicSynthesis ,
Vol. 3 (Eds.: B. M. Trost, I. Fleming), Pergamon Press,
Oxford, 1991, pp. 293; h) M. Kodomari, S. Nawa, T.
Miyoshi, Chem. Commun. 1995, 1895; i) J. Ichihara,
Chem. Commun. 1997, 1921; j) H. J. Lim, G. Keum,
S. B. Kang, Y. Kim, Tetrahedron Lett. 1999, 40, 1547.
3] a) B. Claisen, Ber. Dtsch. Chem. Ges. 1912, 45, 3157;
b) D. S. Tarbell, Org. React. 1944, 2, 1; c) S. J. Rhoads,
N. R. Raulins, Org. React. 1975, 22, 1; d) G. B. Bennett,
Synthesis 1977, 589; e) C. J. Moody, Adv. Hetrocycl.
Chem. 1987, 42, 203; f) F. E. Ziegler, Chem. Rev. 1988,
Scheme 2. Plausible mechanism for Pd-catalyzed allyl cross-
coupling reaction.
Experimental Section
Typical Experimental Procedure
[
To a suspension of indium (114.8 mg, 1.0 mmol), indium(III)
chloride (55.29 mg, 0.25 mmol), lithium chloride (63.5 mg,
1
(
2
.5 mmol), and Pd(PPh3)4 (57.3 mg, 10 mol %) in DMF
1 mL) was added N,N-dimethylbutylamine (101.2 mg,
.0 mmol) and allyl acetate (250.3 mg, 2.5 mmol) at 358C un-
der a nitrogen atmosphere. After 30 min, 1-iodonaphthalene
127.0 mg, 0.5 mmol) in DMF (1 mL) was added and the mix-
8
8, 1423; g) R. K. Hill, AsymmetricSynthesis , Vol. 3,
Ed.: J. D. Morrison), Academic Press, New York,
984, pp. 503; h) F. E. Ziegler, Chem. Rev. 1988, 88,
(
1
(
ture was stirred at 1008C for 9 h. The reaction mixture was
quenched with Na S O (saturated aqueous). The aqueous lay-
1423; i) S. Blechert, Synthesis 1989, 71; j) J. Kallmerten,
M. D. Wittman, Stud. Nat. Prod. Chem. 1989, 3, 233;
k) P. Wipf, Comprehensive OrganicSynthesis , Vol. 5,
(Eds.: B. M. Trost, I. Fleming), Pergamon Press, Oxford,
1991, pp. 827; l) D. Enders, M. Knopp, R. Schiffers, Tetra-
hedron; Asymmetry 1996, 7, 1847.
2
2
3
er was extracted with ether (3ꢀ20 mL), and the combined or-
ganic layers were washed with water and brine, dried with
MgSO , filtered, and concentrated under reduced pressure.
4
The residue was purified by silica gel column chromatography
using n-hexane to give 1-allylnaphthalene; yield: 68.5 mg
1
(
81%). H NMR (400 MHz, CDCl ): d¼8.01 (d, J¼8.08 Hz,
3
[4] T. N. Majid, P. Knochel, Tetrahedron Lett. 1990, 31, 4413.
1
7
1
6
1
1
1
1
H), 7.83 (t, J¼7.76 Hz, 1H), 7.72 (d, J¼6.89 Hz, 1H), 7.50–
.42 (m, 2H), 7.39 (d, J¼7.25 Hz, 1H), 7.32 (d, J¼6.89 Hz,
H), 6.16–6.65 (m, 1H), 5.11–5.06 (m, 2H), 3.82 (d, J¼
[
5] a) J. W. Labadie, D. Tueting, J. K. Stille, J. Org. Chem.
983, 48, 4634; b) J. K. Stille, Angew. Chem. Int. Ed.
1
Engl. 1986, 25, 508; c) A. M. Echavarren, J. K. Stille, J.
Am. Chem. Soc. 1987, 109, 5478; d) J.-B. Verhac, M. Per-
eyre, J.-P. Quintard, Tetrahedron 1990, 46, 6399; e) Y. Ya-
mamoto, S. Hatsuya, J.-i. Yamada, J. Org. Chem. 1990,
13
.30 Hz, 2H); C NMR (100 MHz, CDCl ): d¼135.13,
3
33.27, 132.01, 130.15, 126.84, 125.13, 124.44, 123.96, 123.77,
23.68, 122.19, 114.33, 35.43; IR (film): n¼3003, 2916, 1684,
ꢁ
1
606, 1414, 1358 cm
; HR-EI-MS: calcd. for C H :
13 12
5
5, 3118; f) V. Farina, B. Krishnan, J. Am. Chem. Soc.
68.0939; found: 168.0934.
1
991, 113, 9585; g) P. H. Lee, S.-Y. Sung, K. Lee, Org.
Lett. 2001, 3, 3201; h) K. Lee, J. Lee, P. H. Lee, . J. Org.
Chem. 2002, 67, 8265; i) P. Gomes, C. Gosminiu, J. Peri-
chon, Org. Lett. 2003, 5, 1043.
6] a) J. K. Stille. Pure Appl. Chem. 1985, 57, 1771; b) J. K.
Stille, Angew. Chem. Int. Ed. Engl. 1986, 25, 508; c) M.
Pereyre, J. Quintard, A. Rahm, Tin in OrganicSynthesis ,
Butterworths, London, 1987; d) T. N. Mitchell. Synthesis
Acknowledgements
[
[
This work was supported by the Korea Research Foundation
Grant (KRF-2001-005-D00048). A Brain Pool fellowship
from The Korean Federation of Science and Technology Socie-
ties toDr. M. Sridhar (031-1-20)is gratefully acknowledged. The
NMR and mass data were obtained from the central instrumen-
tal facility in Kangwon National University. We thank Professor
T. Livinghouse of Montana State University for helpful discus-
sions and for checking the manuscript.
1
992, 803; e) V. Farina. V. Krishnamurthy. W. J. Scott.
Org. React. 1997, 50, 1; f) V. Farina, V. Krishnamurthy,
W. J. Scott, The Stille Reaction, Wiley, New York, 1998.
7] a) T. Tabuchi, J. Inanaga, M. Yamaguchi, Tetrahedron
Lett. 1986, 27, 1195; b) B. M. Trost, R. Walchli, J. Am.
Chem. Soc. 1987, 109, 3487; c) Y. Masuyama, N. Kinuga-
wa, Y. Kurusu, J. Org. Chem. 1987, 52, 3702; d) Y. Ma-
suyama, J. P. Takahara, Y. Kurusu, J. Am. Chem. Soc.
References
1
988, 110, 4473; e) J. P. Takahara, Y. Masuyama, Y. Kur-
[1] a) T. K. Devon, A. I. Scott, Handbook of Naturally Oc-
usu, J. Am. Chem. Soc. 1992, 114, 2577; f) K. Yasui, Y.
curring Compounds, Vol. 1, Academic Press, New
Goto, T. Yajima, Y. Taniseki, K. Fugami, A. Tanaka, Y.
1644
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Palladium-Indium-Indium(III) Chloride-Mediated Allyl Cross-Coupling
COMMUNICATIONS
Tamaru, Tetrahedron Lett. 1993, 34, 7619; g) J. Clayden,
M. Julia, Chem. Commun. 1994, 1905; h) X.-R. Li, T.-P.
Loh, Tetrahedron: Asymmetry 1996, 7, 1535; i) Y. Tam-
aru, J. Organomet. Chem. 1999, 576, 215; j) J. A. Mar-
shall, Chem. Rev. 2000, 100, 3163; k) S.-K. Kang, S.-W.
Lee, J. Jung, Y. Lim, J. Org. Chem. 2002, 67, 4376.
[10] a) H. Miyabe, Y. Yamaoka, T. Naito, Y. Takemoto, J.
Org. Chem. 2003, 68, 6745; b) H. Miyabe, Y. Yamaoka,
T. Naito, Y. Takemoto, J. Org. Chem. 2004, 69, 1415.
[11] a) L. P. Lee, K. Bang, K. Lee, C.-H. Lee, S. Chang, Tetra-
hedron Lett. 2000, 41, 7521; b) P. H. Lee, K. Lee, S.-Y.
Sung, S. Chang, J. Org. Chem. 2001, 66, 8646; c) P. H.
Lee, K. Lee, S. Kim, Org. Lett. 2001, 3, 3205; d) P. H.
Lee, H. Ahn, K. Lee, S.-Y. Sung, S. Kim, S. Tetrahedron
Lett. 2001, 42, 37; e) P. H. Lee, S.-Y. Sung, K. Lee, S.
Chang, Synlett 2002, 146; f) N. Iwasawa, T. Miura, K.
Kiyota, H. Kusami, K. Lee, P. H. Lee, Org. Lett. 2002,
4, 4463; g) K. Lee, D. Seomoon, P. H. Lee, Angew.
Chem. Int. Ed. 2002, 41, 3901; h) P. H. Lee, S. W. Lee,
K. Lee, Org. Lett. 2003, 5, 1103; i) P. H. Lee, S. W. Lee,
D. Seomoon, Org. Lett. 2003, 5, 4963; j) T. Miura, K.
Kiyota, H. Kusama, K. Lee, H. Kim, S. Kim, P. H. Lee,
N, Iwasawa, Org. Lett. 2003, 5, 1725; k) P. H. Lee, D. Seo-
moon, K. Lee, Y. Heo, J. Org. Chem. 2003, 68, 2510; l) K.
Lee, H. Kim, T. Miura, K. Kiyota, H. Kusama, S. Kim, N.
Iwasawa, P. H. Lee, J. Am. Chem. Soc. 2003, 125, 9682;
m) P. H. Lee, D. Seomoon, S. D. Kim, K. Nagaiah, S. V.
Damle, K. Lee, Synthesis 2003, 2189.
[
8] a) J. A. Marshall, K. W. Hinkle, J. Org. Chem. 1995, 60,
1
920; b) M. Kimura, I. Kiyama, T. Tomizawa, Y. Horino,
S. Tanaka, Y. Tamaru, Tetrahedron Lett. 1999, 40, 6795;
c) S. Araki, T. Kamei, T. Hirashita, H. Yamamura, M.
Kawai, Org. Lett. 2000, 2, 847; d) U. Anwar, R. Grigg,
V. Sridharan, Chem. Commun. 2000, 933; e) U. Anwar,
R. Grigg, M. Rasparini, V. Savic, V. Sridharan, Chem.
Commun. 2000, 645; f) H. Ohno, H. Hamaguchi, T. Tana-
ka, Org. Lett. 2000, 2, 2161; g) Y. Takemoto, M. Anzai, R.
Yanada, N. Fujii, H. Ohno, T. Ibuka, Tetrahedron Lett.
2
001, 42, 1725; h) S. Araki, K. Kameda, J. Tanaka, T. Hir-
ashita, H. Yamamura, M. Kawai, J. Org. Chem. 2001, 66,
919; i) M. Anzai, R. Yanada, N. Fujii, H. Ohno, T. Ibu-
7
ka, Y. Takemoto, Tetrahedron 2002, 58, 5231; j) T.-S.
Jang, G. Keum, S. B. Kang, B. Y. Chung, Y. Kim, Syn-
thesis 2003, 775; k) P. Gomes, C. Gosmini, J. Perichon,
Synthesis 2003, 1909; l) S. Araki, S. Kambe, K. Kameda,
T. Hirashita, Synthesis 2003, 751.
[12] a) R. McCrindle, G. Ferguson, G. J. Arsenault, A. McA-
lees, Chem. Commun. 1983, 571; b) L. A. T. Cleghorn,
I. R. Cooper, R. Grigg, W. S. MacLachlan, V. Sridharan,
Tetrahedron Lett. 2003, 44, 7969.
[
9] I. R. Cooper, R. Grigg, W. S. MacLachalan, M. Thorn-
ton-Pett, V. Sridharan, Chem. Commun. 2002, 1372.
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