COPPER 1
Cyclopropanes. In the presence of copper, Ä…-diazo ketones
Copper1
decompose and react with alkenes to yield cyclopropyl ketones
by intermolecular or intramolecular cyclization.13 Also, copper
Cu
assists the reaction of alkenes with gem-dihalides to produce
cyclopropanes.14
[7440-50-8] Cu (MW 63.54)
Nitriles. Nitriles may be prepared from aromatic aldehydes
InChI = 1/Cu
by reaction with copper powder and ammonium chloride (in situ
InChIKey = RYGMFSIKBFXOCR-UHFFFAOYAN
preparation of CuCl2 and NH3).15
(reagent for the cyclization and/or coupling of various functional
groups;1 decarboxylation;10 preparation of Ä…-alkynic alcohols;12 Ketones. The formation of ketones has been reported to result
cyclopropanes,13 nitriles,15 ketones by benzylic oxidation10)
from benzylic oxidation using a copper powder catalyst (eq 1).16
The initial oxidized product (2) may further cyclize to (3) by
ć%
Physical Data: mp 1083 C; d 8.94 g cm-3.
continued use of the same reagent. The latter reaction is similar
Solubility: slowly sol aq NH3.
to tetramethoxydibenzofuran formation resulting from heating
Form Supplied in: reddish, lustrous solid; ingots, sheets, wire, or
4-bromo-5-iodoveratrole with copper in nitrobenzene.17
powder (most synthetic reactions require the use of the powder
form); widely available.
XX
Analysis of Reagent Purity: by electrolytic assay,21 or EDTA/ O2NNO2 Cu, DMF
iodometric titration.1d
Handling, Storage, and Precautions: should be stored in the
X = Br or I
(1)
absence of moisture; in moist air it gradually becomes coated
with copper carbonate. The powder may be flammable when
XX
O2NNO2 Cu O2N O NO2
exposed to excessive heat or flame.
(1)
DMF
air
O O
(2) (3)
Original Commentary
Other minor reactions of copper include its use as a catalyst
Edward J. Parish
in the synthesis of azo compounds from diazonium tetrafluorobo-
Auburn University, Auburn, AL, USA
rates,18 rearrangements of bicyclic hydrocarbons,19 and in the
classic Gattermann version of the Sandmeyer reaction for the
Ullmann Reaction. Alkyl halides containing electron-attrac-
conversion of arenediazonium salts to halides.20
ting substituents may be coupled in the presence of copper in good
yields.1 The reaction is believed to proceed through organocopper
intermediates, in an oxidant addition, rather than radicals.2 Details
for the activation of the copper catalyst by iodine in acetone are
First Update
described along with the Ullmann coupling of 2-chloronitro-
benzene to yield 2,2 -dinitrobiphenyl.3 Dawei Ma
Procedures for the preparation of unsymmetrical biaryls from a Shanghai Institute of Organic Chemistry, Shanghai, P. R. China
mixture of halides have been described.4 Similarly, the coupling
of vinyl bromides by copper in a stereospecific synthesis of con- Ullmann Reaction. Copper powder is a traditional catalyst for
jugated dienes has also been reported.5 A highly reactive copper Ullmann-type coupling reactions.22 It is recognized that Cu(0) can
powder has been developed that is particularly effective for Ull- be oxidized into Cu(I), which serves as the catalytic species.22
mann reactions.6 As a result, in recent studies on Ullmann-type coupling reac-
Other Ullmann-type coupling reactions include the reaction tions, several Cu(I) sources such as CuI have been usually em-
of phenols with aryl halides to yield diaryl ethers,7 the synthe- ployed as the catalyst.23 In some cases copper powder is still
sis of triarylamines through the coupling of diarylamines with utilized.
aryl halides,8 the cross coupling of allylic and benzylic bro- Under the action of a stoichiometric amount of copper
mides with acid chlorides,6b and the cyclization of epoxyalkyl powder, an intramolecular Ullmann coupling reaction of aryl
halides.9 iodides occurs to provide the cyclization products in good yields,
which, upon treatment with KOH in dioxane and water, produce
Decarboxylation. Commercial copper powder in quinoline acyclic biphenyls (eq 2).24 This template-directed strategy allows
solution is a standard reagent for decarboxylation reactions.10 In the assembly of unsymmetrical biphenyls without formation of
some instances, decarboxylation and dehydration occur to produce the by-products, which are produced in many intermolecular
an exocyclic alkene.11 coupling reactions. Dimerization of 2,4-dibromothiophene in the
presence of Cu powder in DMF gives a 32% yield of 4,4 -dibromo-
Ä…
Ä… 2,2 -bithiophene.25
Ä…-Acetylenic Alcohols. Heating 1,4-diformyloxy-2-butyne
with copper and adipic acid followed by treatment with acid and Using water as the solvent, coupling of o-chlorobenzoic acid
methanol gives 2-butyn-1-ol.12 and aniline with copper powder as the catalyst delivers N-
Avoid Skin Contact with All Reagents
2 COPPER
phenylanthranilic acid (eq 3);26 while 2-chlorobenzoic acids are
O +
R2 2
R2 2 2
converted into the corresponding salicylic acid derivatives with N
R2 Me
[1,2] shift
Cu/R2 2 R2 2 2 NMe
R
water under the catalysis of Cu powder (eq 4).27 In the latter case,
R
_
R2
N2
pyridine is used as a cocatalyst and the reaction is assumed to go
O
through a typical Ullmann coupling process.
R = OEt, Ph
R
R2 R2 2 2
R R2 2
(6)
N
O
Cu/DMF
O Me
I O
I reflux
O
O
O O
S
Cu/MX
-
(7)
ArX
R2 Ar-N2+
N
X = SCN, Cl, Br, I
S
O
O
R
R
O
KOH Radical Initiation. Cu(0)-catalyzed addition of alkyl Ä…-iodo-
CO2H
(2)
carboxylates and Ä…-iodoalkanenitriles to alkenes in the absence
O
CO2H
O
of solvent produces Å‚-lactones and ²-iodo-alkanenitriles (eq 8).
The reaction is assumed to be initiated by electron transfer from
O
R2
copper to the activated haloalkane.32 Similarly, additions of
R2
perfluoroalkyl iodides to a variety of unsaturated alcohols and
simple olefins (eq 9),33 and Michael-type reactions of ethyl
CO2H
Cu/K2CO3
bromodifluoroacetate with Ä…,²-unsaturated carbonyl compounds
+
water
(eq 10),34 are catalyzed efficiently by copper powder. In addition, a
H2N
Cl
copper-mediated coupling reaction of 1-iodoperfluorooctane with
CO2H
halophenols may also go through a radical mechanism (eq 11).35
(3)
Ph
X
R2 2
N
Cu/R2 2 R2 2 2 CIX I
-EtI
H
R2 2 2
X = CN, CO2Et X = CO2Et
R R2
R R2
R2 2 CO2H
R2 2 CO2H
Cu/K2CO3
(4)
O
pyridine/water
R2 OH
R2 Cl
R2 2
(8)
R
R
O
R2 2 2
R R2
Cyclopropanes. Cu(0) generated from electrochemical
reduction of CuBr is found to effectively catalyze the reaction
Cu powder
of activated olefins with activated polyhalo compounds to form
RFCH2CHIR2 (9)
RFI + CH2=CHRR2
polysubstituted cyclopropanes (eq 5).28 Copper carbenoids are
proposed as the key intermediates. The main advantage of this
reaction is that it does not require the use of hazardous, toxic,
O
O
or not easily prepared reagents such as diazo compounds or
Cu powder
diazirines.
(10)
BrCF2CO2Et
R R2
Cu(0)
CF2CO2Et
+ RR2 CCl2 (5)
W
W
R
R
Cu
Diazo Decomposition. Decomposition of diazoketones or C8F17I + (11)
OH
OH
diazoesters with copper powder in the presence of tertiary amines
X
C8F17
produces transient ammonium ylides, which undergo facile N
R2
R2
to C [1,2] shift to give Ä…-substituted Ä…-amino ketones or Ä…-amino
esters (eq 6).29 The ability of copper powder to promote diazo
decomposition is also observed in the transformation of dry arene- Insertion to C X Bonds. Rieke and Ebert have developed
diazonium o-benzenedisulfonimides into the corresponding aryl a highly activated copper(0),36,37 which permits the direct for-
thiocyanates30 or aryl halides31 (eq 7). mation of a wide range of organocopper compounds from the
A list of General Abbreviations appears on the front Endpapers
COPPER 3
respective organic halides without using traditional organolithium copper(I) salts, which may result from the reduction of copper(II)
or Grignard precursors. This activated Cu(0) is obtained by salts with copper powder.
reduction of an ethereal solution of CuI·PR3,36 or CuCN·LiCl,37
OH
with an ethereal solution of preformed lithium naphthalenide or
Cu/Cu(ClO4)2
biphenylide (eq 12).
R X
+
ether, rt
Cu(0) + Np + LiX + L (12)
LiNp + CuXL
OH R OH
The Cu(0) generated from this system is sufficiently reactive
to allow direct oxidative addition of alkyl and aryl halides. The
+
(19)
resulting organocopper intermediates can react with acyl chlo-
rides, aldehydes, epoxides, and Ä…,²-unsaturated ketones, to pro-
R
duce the corresponding ketones (eq 13), alcohols (eq 14), 1,4-
addition products (eq 15), and ring-opening products (eq 16).37
Cu/CuCl2
Dehalogenation of aryl halides occurs when they are treated with R
+ ArNO
PhHN R (20)
dioxane, reflux
the above activated Cu(0) and then quenched with water.38 Fur-
thermore, copper benzoates are prepared via oxidative addition
of aryl iodides with activated Cu(0) and subsequent reaction with
Triazole Formation. Copper-catalyzed [3 + 2] cycloaddi-
carbon dioxide at room temperature. These may be acidified to
tion of terminal alkynes and azides is a reliable method for
produce the functionalized aryl carboxylic acids, or treated with
quickly elaborating 1,4-substituted [1,2,3]-triazoles. CuSO4 and
appropriate alkyl halides in the presence of a dipolar aprotic sol-
sodium ascorbate, which generate the catalytic Cu(I) species, have
vent to generate the corresponding aryl esters (eq 17).39
often been employed as the catalytic system.41 It is found that
Cu(0) then ArCOCl
the combination of activated Cu(0) nanosize powder and triethy-
RBr RCOAr (13)
lamine hydrochloride salt is an alternate catalytic system for the
Cu(0) then ArCHO
above transformation (eq 21).42 The reaction works well in a H2O/
(14)
RBr RCH(OH)Ar
t-BuOH solution to afford 1,4-substituted [1,2,3]-triazoles in great
diversity. The presence of triethylamine hydrochloride is recog-
R R2 2
Cu(0) then
RBr nized to enhance the dissolution of Cu(0) resulting in the facile
(15)
R2 2
R2 generation of the catalytic Cu(I) species. Thus, when substrates
R2 O bearing an amine hydrochloride moiety are utilized, the addition
O
of triethylamine hydrochloride is not necessary (eq 22).43
OH
Cu(0) then N3 OH
Cu(0)/Et3N·HCl
(16)
RBr R
+
O R2
H2O/t-BuOH
R2
CO2H
83%
Cu(0) then CO2
ArCOOH (or R)
(17)
ArI
H+ or RX N
N
Ph
NOH
Besides carbon-halogen bonds, insertion of activated Cu(0)
(21)
into C O bonds of allylic esters is observed. The resultant
CO2H
allylic organocopper reagents attack aldehydes to provide
homoallyl alcohols (eq 18).37 It is noteworthy that for sterically
hindered allylic esters, the yields are considerably lower when
compared to those obtained with the corresponding allyl chlo-
Cu(0)
·HCl
N N3
+
rides.
H2O/t-BuOH
93%
R2 2 R2 2 OH
Cu(0) then
R OAc R
(18)
Ph
PhCHO
N·HCl
R2 R2 N
N
N
(22)
Allylation. Phenols can be allylated at the ortho-position by
use of a mixture of copper powder and anhydrous copper(II)
perchlorate (eq 19).40 The advantages of these particular con-
ditions are the use of a near neutral medium and the formation
of less p-allylated phenols. Under the action of a mixture of cop-
per powder and CuCl2·2H2O (1:4 molar ratio), allyl amines are Organic Halides. Primary alcohols are converted
obtained from alkenes and nitrosoarenes (eq 20).41 The real cat- into primary alkyl halides with Cu, Fe, CuBr(phen)2, and CX4
alytic species in these two reaction systems are assumed to be (X = Cl or Br) in DMF at room temperature (eq 23).44 Under
Avoid Skin Contact with All Reagents
4 COPPER
these reaction conditions, only alkyl formates are generated from 1. (a) Fanta, P. E., Chem. Rev. 1964, 64, 613. (b) Fanta, P. E., Synthesis 1974,
9. (c) Sainsbury, M., Tetrahedron 1980, 36, 3327. (d) Miayano, S.; Tobita,
secondary alcohols, while ²-halo-Ä…,²-unsaturated ketones are
M.; Hashimoto, H., Bull. Soc. Claim. Fr., Part 2 1981, 54, 3522; Synth.
obtained from ²-diketones (eq 24), and no conversion of ethyl
Commun. 1993, 23, 2463. (e) Dictionary of Organometallic Compounds;
acetoacetate is observed. These transformations may go through
Buckingham, J., Ed.; Chapman & Hall: New York, 1984; Vol. 1, p
a typical carbene route, or may involve an iminium salt pathway.
569. For reviews of properties, uses, and inorganic chemistry of copper,
see, e. g. (f) Massey, A. G. In Comprehensive Inorganic Chemistry;
Cu/Fe/CuBr(phen)2
Trotman Dickenson, A. F., Ed.; Pergamon: New York, 1973; Vol. 3, p
RCH2X (23)
RCH2OH
CX4, DMF, rt 1. (g) Tuddenham, W. M.; Dougall, P. A. In Kirk-Othmer Encyclopedia
of Chemical Technology, 3rd ed.; Wiley: New York, 1979; Vol. 6, p 819.
For further reviews of the use of copper in organic synthesis, (h) see, e. g.
O X
O O
Cu/Fe/CuBr(phen)2
Young, G. B. In Comprehensive Organometallic Chemistry; Wilkinson,
(24)
CX4, DMF, rt G.; Stone, F. G. A.; Abel, E. W., Eds.; Pergamon: New York, 1982; Vol.
RR
RR
9, p 1529 and references cited therein.
2. (a) Cohen, T.; Poeth, T., J. Am. Chem. Soc. 1972, 94, 4363. (b) Cohen,
T.; Cristea, I., J. Am. Chem. Soc. 1976, 98, 748.
Catalytic Hydrogenation. Selective reduction of C=C
3. Fuson, R. C.; Cleveland, E. A., Org. Synth., Coll. Vol. 1955, 3, 339.
double bonds possessing different substituents is a valuable trans-
4. (a) Brown, E.; Robin, J.-P., Tetrahedron Lett. 1977, 2015. (b) Brown, E.;
formation for organic synthesis. Chemoselective hydrogenation of
Robin, J.-P.; Tetrahedron Lett. 1978, 3613.
the C=C double bond of Ä…,²-unsaturated ketones without com-
5. (a) Cohen, T.; Poeth, T., J. Am. Chem. Soc. 1972, 94, 4363. (b) Lewin,
promising an isolated C=C double bond is achieved with a com-
A. H.; Zovko, M. J.; Rosewater, W. H.; Cohen, T., J. Chem. Soc., Chem.
bination of Cu and Al2O3 as the catalyst.45 Further investiga- Commun. 1976, 80.
tion revealed that Cu/SiO2 is better for suppressing side reactions
6. (a) Rieke, R. D.; Rhyne, L. D., J. Org. Chem. 1979, 44, 3445. (b) Ebert,
(eq 25).46 These catalytic systems are prepared from cupriammo- G. W.; Rieke, R. D., J. Org. Chem. 1984, 49, 5280.
nium solution and porous Al2O3 or silica gel. In latter case, most
7. (a) Ungnade, H. E.; Orwoll, E. F., Org. Synth., Coll. Vol. 1955, 3, 566.
(b) Lindley, J., Tetrahedron 1984, 40, 1433.
Ä…,²-unsaturated ketones only give saturated ketones, however,
reduction of a C=O double bond was noted in one substrate 8. (a) Hager, F. D., Org. Synth., Coll. Vol. 1941, 1, 544. (b) Gauthier, S.;
Fréchet, J. M. J., Synthesis 1987, 383.
(eq 26). If saturated ketones are used, the corresponding alco-
9. (a) Wu, T.-C.; Rieke, R. D., Tetrahedron Lett. 1988, 29, 6753. (b) Rieke,
hols are obtained in good yields under similar reaction conditions
R. D.; Wehmeyer, R. M.; Wu, T.-C.; Ebert, G. W., Tetrahedron 1989, 45,
(eq 27).47
443.
10. (a) Manecke, G.; Rotter, U., Chem. Ber. 1973, 106, 1116. (b) Smith, N.
O
R.; Wiley, R. H., Org. Synth., Coll. Vol. 1963, 4, 337. (c) Burness, D. M.,
Cu/SiO2, H2
Org. Synth., Coll. Vol. 1963, 4, 628. (d) Wiley, R. H.; Smith, N. R., Org.
Synth., Coll. Vol. 1963, 4, 731. (e) Walling, C.; Wolfstirn, K. B., J. Am.
toluene, 90 °C, 5 h, 96%
Chem. Soc. 1947, 69, 852.
11. Vilkas, M.; Abraham, N. A., Bull. Soc. Chem. Fr., Part 2 1960, 1196.
O
12. Himmele, W.; Fliege, W.; Fröhlich, H., Synthesis 1973, 615.
Ø
(25) 13. (a) Novák, J.; Ratuskż, J.; Sneberk, V.; SO
rm, F., Collect. Czech. Chem.
Commun. 1957, 22, 1836. (b) Ratuskż, J.; SO
rm, F., Collect. Czech.
Chem. Commun. 1958, 23, 467. (c) Novák, J.; SO
rm, F., Collect. Czech.
Chem. Commun. 1958, 23, 1126. (d) Stork, G.; Ficini, J., J. Am. Chem.
Soc. 1961, 83, 4678. (e) Doering, W. Von E.; Fossel, E. T.; Kaye, R.
O L., Tetrahedron 1965, 21, 25. (f) Baldwin, J. E.; Fogelsong, W. D.,
OH
Cu/SiO2, H2
Tetrahedron Lett. 1966, 4089. (g) Monahan, A. S., J. Org. Chem. 1968,
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33, 1441.
toluene, 90 °C, 9 h, 94%
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2676.
15. Capdevielle, P.; Lavigne, A.; Maumby, M., Synthesis 1989, 451.
C8H17-n 16. Farrell, P. G.; Moskowitz, D.; Terrier, F., Synth. Commun. 1993, 23, 231.
17. Baker, W.; Barton, J. W.; McOmie, J. F. W.; Penneck, R. J.; Watts, R. L.,
J. Chem. Soc 1961, 3986.
Cu/SiO2, H2
18. Cadogan, J. I. G.; Hibbert, P. G.; Siddiqui, M. N. U.; Smith, D. M., J.
toluene, 60 °C, 2.5 h, 100%
Chem. Soc., Perkin Trans. 1 1972, 2555.
O 19. Burger, U.; Mazenod, F., Tetrahedron Lett. 1976, 2885.
H
C8H17-n 20. Bigelow, L. A., Org. Synth., Coll. Vol. 1941, 1, 135.
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HO
H
I. P.; Cheprakov, A. V., Coord. Chem. Rev. 2004, 248, 2337.
24. Takahashi, M.; Ogiku, T.; Okamura, K.; Da-te, T.; Ohmizu, H.; Kondo,
Related Reagents. Copper Bronze; Sodium Iodide Copper. K.; Iwasaki, T., J. Chem. Soc., Perkin Trans. 1 1993, 1473.
A list of General Abbreviations appears on the front Endpapers
COPPER 5
25. Wegener, P.; Litterer, H. DE4105898 A1 (Chem. Abstr. 1997, 117, (d) Ginah, F. O.; Donovan, T. A.; Suchan, S. D.; Pfennig, D. R.; Ebert,
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32, 2055.
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Chem. 1993, 58, 2492.
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38. Ebert, G. W.; Pfennig, D. R.; Suchan, S. D.; Donoven, T. A.; Aouad, E.;
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31. Barbero, M.; Degani, I.; Dughera, S.; Fochi, R., J. Org. Chem. 1999, 64,
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Avoid Skin Contact with All Reagents