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Anaerobic Copper-Catalyzed Oxidation of Alcohols to Aldehydes and Ketones.

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E. D. Jemmis, B. Kiran, J. Org. Chem. 1996,6f, 9006.
For such a distorted (5 framework see L. D. Mohler, K. P. Vollhardt, S . Wolff,
Angew Chem. 1990, f02, 1200; Angew. Chem. h t . Ed. Engl. 1990, 29, 1151
The variable 6R is defined as A R - ARSm,=.Using this definition and parabolic
equations for the energy curves, one obtains E, = 0.5 k,(6R)' for the (5 curve,
and E, = 0.5 k , (6R - 6 R J 2+ const for the ~i curve; 6R. is the deviation of the
maximum or minimum of the K curve from the ff minimum at 6R = 0. The
curve of the total energy E,,, (the sum of ff and K energies) is then given by
0.5kO(6R)*+0.5 k.(6R - 6RJ* +const, and its minimum by Equation (1).
a) A. G. Ozkabak, L. Goodman, J. M. Berman, Chem. Phys. Lett. 1990,168,
253; b) for a summary, see S . Shaik, S . Zilberg, Y. Haas, Ace. Chem. Res. 1996,
29, 211.
Anaerobic Copper-Catalyzed Oxidation of
Alcohols to Aldehydes and Ketones**
Istvan E. Marko,* Masao Tsukazaki, Paul R. Giles,
Stephen M. Brown, and Christopher J. Urch
We recently reported on an efficient, copper-catalyzed oxidation of alcohols to carbonyl compounds that uses oxygen or air
as the ultimate, stoichiometric oxidant.['] In light of the extensive research on copper chemistry[21and some of our own mechanistic studies,C3' we proposed the catalytic cycle depicted in
Figure 1.
H 0 - p
copper(1) derivative 4 then undergoes an intramolecular hydride
transfer reaction leading to complex 5 and the formation of a
carbon-oxygen double bond.[41Release of the bound carbonyl
compound 6 generates the hydrazidocopper(1) system 7 which,
in the presence of oxygen, is subsequently oxidized to the binuclear copper(I1) complex 8.['] Homolytic cleavage of the peroxo
linkage, enables the second intramolecular hydrogen-atom
transfer of the catalytic cycle, which affords the hydroxycopper(r) derivative 9 and leads to the regeneration of the key diazo
functionality. Addition of alcohol 2 with concomitant loss of
water leads to reformation of the loaded catalyst 4 and a new
catalytic cycle ensues.
As this mechanism suggests, in the absence of the azo derivatives 3, little if any turnover was observed.[61The key role played
by the azodicarboxylates 3 (DEAD: Z = COOEt, DIAD:
Z = COOiPr and DBAD; Z = COOtBu) is apparent from the
catalytic cycle. They act both as hydride acceptors in step 1 and
also as ligands for the metal in the various complexes involved
in the oxidation process. The continuous regeneration of 3 in the
presence of oxygen ensures efficient turnover.
In order to gain more information on the hydride transfer
(step 1) and thereby to substantiate our proposed mechanism,
we decided to perform some experiments in the absence of oxygen. Under these anaerobic conditions, the conversion of alcohol 2 into carbonyl compound 6 should stop once the azo
derivative 3 has been reduced. Reoxidation of the intermediate
copper-hydrazine complex 7 to the active species 4 cannot occur and the reaction should cease after 3 is consumed.[71An
equimolar quantity of hydrazine 10 should also be produced in
this process. For catalysis to still take place under these anaerobic conditions, a ligand exchange between the hydrazidocopper(1) complex 7, alcohol 2 and azo compounds 3 should operate
with simultaneous generation of hydrazine 10 (step 6) .[81
To test these hypotheses, we performed some initial experiments onp-chlorobenzyl alcohol 11. The most important results
are displayed in Table 1.
/o""" - DCH0
Table 1. Influence of the azo derivative 3 on the copper-catalyzed, anaerobic oxidation of alcohols [a].
R, R' = alkyl, aryl. H;3a:2 = COOEt. 3b: Z = C00Pr. 3c: Z = COOBu; L,= phen
3 [molX]
Conversion ["h] [b]
Ratio 12/13 [c]
>99 [d]
>9 9 / < 1
>9 9 / < 1
>9 9 / < 1
Figure 1. Proposed mechanism for the copper-catalyzed oxidation of alcohols.
In this catalytic process, we assumed that the reaction of
CuC1.phen (phen = 1,lO-phenanthroline) with the alcohol 2
and azodicarboxylate 3 forms the ternary complex 4. This
Prof. 1. E Mark& Dr. M. Tsukazaki, Dr. P. R Giles
Departement de Chimie
Universite Catholique de Louvain
Place Louis Pasteur 1, B-1348 Louvain-la-Neuve (Belgium)
Fax: Int. code +(10)47 27 88
Dr. S . M. Brown
Zeneca Process Technology Department, Huddersfield Works,
Huddersfield (UK)
Dr. C. J. Urch
Zeneca Agrochemicals, Berkshire (UK)
This work was supported by Zeneca Limited, through the Zeneca Strategic
Research Fund. I. E. M. is grateful to Zeneca for a Zeneca Fellowship
(1994- 1997).
0 WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1997
[a] 20 'C; other conditions see Experimental Section. [b] Determined by 'H NMR
spectroscopy. [c] Determined by 'H NMR spectroscopy and by capillary gas chromatography. [d] Aldehyde 12 was isolated in 82% yield.
Addition of one equivalent of alcohol 11 to a suspension
containing 5 mol% CuCl.phen, 10 moly0 DBAD 3c, and
10 mol% K,CO, in toluene, in the absence of oxygen, led to the
partial transformation of 11 into aldehyde 12 (11 YOconversion,
Table 1, entry 1). Raising the quantity of DBAD 3c (50 mo1Y0)
used resulted in an increase in the yield of the aldehyde (entry 2).
Finally, when DBAD 3c (1.2 equiv) was used, a quantitative
conversion was observed and high yields of p-chlorobenzalde-
0570-0833/97/3620-2208 $17.50+ .50/0
Angew. Chem. Int. Ed. Engl. 1997, 36,
No. 20
corresponding p-amino aldehydes without any detectable
racemization (Table 2, entry lo), which demonstrates the mildness of the reaction conditions.["] In contrast to the aerobic
oxidation system"] in which two equivalents of K,CO, were
required for optimum catalytic activity, only a small amount of
K,CO, (10 mol%) is necessary in our anaerobic version. Remarkably, in all cases studied so far, complete conversion of the
alcohol to the carbonyl derivative took place. This situation is
different in the aerobic process in which the presence of oxygen
hampers complete transformation of primary alcohols to aldehydes.1'21
In summary, we have established a new, efficient copper-catalyzed anaerobic protocol for the oxidation of a wide range of
alcohols into carbonyl compounds under mild conditions. In
addition, these studies support our proposals for the mechanism
of such Cu-catalyzed oxidations and form the foundations for
the development of this interesting oxidation system.
hyde 12 were obtained (Table 1, entry3). One equivalent of
DBADH, was also produced in this last reaction. Whilst the use
of one equivalent of DIAD 3b also resulted in complete consumption of 11, the mixed carbonate 13 was now the major
product (Table 1, entry 4). The amount of 13 increased even
further when DEAD 3a was employed instead of DIAD 3b
(Table 1, entry 5 ) . Thus, to avoid the undesired formation of
carbonate 13, a bulky carboalkoxy residue is required on the azo
derivatives 3. DBAD 3c therefore appears to be the best adjuvant and all subsequent oxidations were performed with this
diazo compound.[91
In addition to substantiating our proposed mechanism, the
anaerobic, copper-catalyzed oxidation system proved to be particularly useful for 1:he iaboratory-scale oxidation o f a wide variety of alcohols into the corresponding carbonyl derivatives
(Table 2).
As can be seen from Table 2, primary, secondary, allylic, and
benzylic alcohols can all be smoothly oxidized to the corresponding aldehydes and ketones in excellent yields. Sensitive
products, such as geranial and neral are not isomerized under
the reaction condilions (Table 2, entries 3 and 4,respectively).
Remarkably, benzoin is oxidized to benzil with virtually no
competitive C-C bond cleavage (Table 2, entry 9) .[*'I Importantly, optically active p-amino alcohols are oxidized to the
Experimental Section
Typical procedure for the oxidation of 2-undecanol to 2-undecanone: CuCl(5 mg,
0.05mmol) and 1,lO-phenanthroline (9 mg, 0.05 mmol) were mixed in dry toluene
( 5 mL) and the mixture was stirred for 10 min at room temperature. K,CO, (14 mg,
were added successively and the mixture was heated at 70 'C for 3 h. After cooling
to room temperature, the mixture was diluted by adding Et,O ( 5 mL) and filtered
through a pad of celite. Evaporation of the solvent under vacuum afforded a crude
product that was further purified by column chromatography (EtOAcihexane 1/20)
to give pure 2-undecanone (142 mg, 84%).
Table 2. Anaerobic, copper-catalyzed oxidation of alcohols [a].
R' H
Received: March 20. 1997 [Z102651E]
German version- Angen. Chem. 1997. 109,2297-2299
Product 6
Substr.ite 2
Keywords: alcohols carbonyl compounds
homogeneous catalysis * oxidations
Yield Wl[b] I
60 [dl
60 [el
180 [f]
CoHl9 P C H 3
P h G0 p h
120 [f]
120 kl
[a] 70"C; other conditions see Experimental Section. [b] All yields are for pure, isolated
products. [c] Reaction performed at 20°C [d] >95% ( E ) .[el > 9 5 % ( Z ) .[fl Reaction conducted under degassed conditions. [g] > 95 % ee.
Angeu Chem In/ Ed
Engl 1997.36, No 20
0 WILEY-VCH Verlag GmbH,
[l] 1. E. Marko, P. R. Giles, M. Tsukazaki, S. M Brown, C J. Urch,
Science 1996,274,2044-2046.
[2] a)C. Jallabert, H. Riviere, Tetrahedron Lett. 1977.1215- 1218; b)C.
Jallabert, C Lapinte, H. Riviere, J. Mol. C a r d 1980, ' 127- 136;
c) C. JalLabert, H. Riviere, Tetrahedron 1980.36, I19I - t 194; d) C.
Jallabert, C. Lapinte, H. Riviere, J Mol. Cutai. 1982, 14, 75-86; e )
P. Capdevielle, D. Sparfel, J. Baranne-Lafont. N. K. Cuong, M.
Maumy, J. Chem. Res. Synop. 1993, 10-11, and references therein;
f) M. Munakata, S . Nishibayashi, H. Sakamoto, 3. Chem. Soc.
Chem. Commun. 1980, 219-220; g) S. Bhaduri, N.Y. Sapre, J
Chem. Soc. Dalton Trans. 1981, 2585-2586; h) M. F. Semmelhack,
C. R. Schmid, D. A. Cortes, C. S . Chou, J. Am. Chem. Soc. 1984,
106, 3374-3376.
[3] I. E. Marko, P. R. Giles, M. Tsukazaki, S. M. Brown, C. J. Urch,
unpublished results.
[4] For general reviews on Oppenauer-type oxidations, see a) C. F.
de Graauw, J. A. Peters, K . Vandekkum, J. Huskens, Synthesis
1994,1007-1017; b) C. Djerassi, Org. Reacr. IV Y 1951.6.207-212;
c) K. Krohn, B. Knauer, J. Kupke, D. Seebdch, A. K. Beck, M.
Hayakawa. Synthesis 1996, 1341-1344 The use of stoichiometric
amounts of dipiperidinyl azodicarboxamide to oxidize magnesium
alkoxides to the corresponding carbonyl compounds has been described: K. Narasaka, A. Morikawa, K. Saigo, T Mukaiyama, Bull.
Chem. Soc. Jpn. 1971, 50, 2773-2776. No reaction is observed under our catalytic anaerobic conditions if DBAD is replaced by the
azodicarboxamide derivative. The stoichiometric oxidation of copper(1) alkoxides to aldehydes and ketones by O,, though in very low
yields, has been reported previously: P. Capdevielle, P. Audebert,
M Maumy, Tetrahedron Letf. 1984, 2s.4397-4400.
[ S ] For reviews on the formation, isolation and reactions of dinuclear
copper@) peroxides, see a) K. D. Karlin, Y. Gultneh. Prog. Inorg.
Chem. 1987, 35,219-327; b) A. D. Zuberbuhlrr in Copper Coordinarion c h e m i s l r j ~Biochemical
and Inorganic Perspectives (Eds. :
K. D Karlin, J. Zubieta), Adenine Press, Guilderland, NY, 1983;
c) A. M. Sakharov, I. P. Skibida, Kine/. Curd. Engl. Trans/.
1988, 29, 96-102; d) 2. Tyleklar, R. R. Jacobson. N. Wei, N. N.
Murthy, J. Zubieta, K. D . Karlin, J Am. Chrm. Sor. 1993. 115,
2677-2689; e) N. Kitajima, K. Fujisawa, C. Fujimoto, Y Morooka, S. Hashimoto, T. Kitagawa, K. Toriumi, K. Tatsumi, A. Nakamura, ihid. 1992, 114, 1277-1291; f) S. Fox. A. Nanthakumar,
D-69451 Weinheim, 1997
0570-083319713620-2209 S 17 50+ 5010
M. Wikstrom, K. D. Karlin, N. J. Blackburn, ibid. 1996, ff8,24-34; g) E. I.
Solomon, U. M. Sundaram, T. E. Machonkin, Chem. Rev. 1996, 96, 25632605.
[6] In the absence of azo derivatives 3 highly active benzylic alcohols undergo
some aerobic oxidation to the corresponding aldehydes. For example, using
5mol% CuCI.phen, 200mol% K,CO,, benzene, S OT , and bubbling 0,
through the reaction mixture, a 60 % conversion ofp-chlorobenzylalcoholinto
p-chlorobenzaldehyde can be achieved. Allylic substrates gave much lower
conversions (<30%) and aliphatic alcohols are virtually inert under these
conditions. No reaction is observed with any of these substrates under anaerobic conditions, in the absence of the azo derivatives 3.
171 The intermediacy of complex 7 in the aeroblc oxidations was supported by the
following observations: 1) independently generated hydrazido complex 7 (CuCI.phen/DBADH,/NaH) proved to be unreactive under anaerobic conditions;
2) passing 0, through the reaction mixture containing 7 and alcohol 2 restored
the catalytic activity, and good yields of aldehyde 6 were again obtained.
[8] This new catalytic cycle, involving steps 2 and 6, is in some ways reminiscent
of analogous oxidation shunts that take place in aerobic bacteria placed under
anaerobic conditions.
[9] The oxidation of alcohols with azodicarboxylates has been previously reported: F. Yoneda, K. Suzuki, Y Nitta, J Org. Chem. 1967,32,727-729. Control
experiments were therefore performed to establish the need for copper salts in
our anaerobic oxidation procedure. Thus, under our reaction conditions, no
aldehyde or ketone could be detected in the absence of the CuCI’phen catalyst,
even when phenanthroline was added as an activating base. Moreover, certain
reactive alcohols were oxidized partially by CuC1.phen in the absence of the
azo derivative 3, though only in moderate yields.
[lo] With most oxidants, 2-hydroxyketones are oxidized with concomitant cleavage
of the C-C bond: a) R. C. Larock, ComprehensiveOrganic Tran.formations,
VCH, New York, 1989, pp. 604-615; b) R. A. Sheldon, J. K. Kochi, MetalCatalyzed Oxidations of Organic Compounds, Academic Press, New York.
1981; c) G. Procter in Comprehensive Organic Synthesis, Vol. 7 (Eds.: B. M.
Trost, I. Flemming, S . V. Ley), Pergamon, Oxford, 1991; d) W. S . Trahanovsky, Oxidation in Organic Chemistry, Part A - D , Academic Press, New
[ll] See for example M. T. Reetz, M. W. Drewes, A. Schmitz, Angew Chem. 1987,
99, 1186-1188; Angeu,. Chem. Int. Ed. Engl. 1981,26, 1141-1143.
[12] This difference appears to be due to competitive autooxidation of the aldehyde
to the corresponding carboxylic acid by oxygen at high conversions of the
alcohol. See also ref. [9b].
Electron-Density Relaxation and
Oppositely Signed Reaction Constants
in Dual Substituent Parameter Relationships
in Dediazoniation Reactions**
Rainer Glaser,* Christopher J. Horan, and
Heinrich Zollinger*
Dedicated to Professor Dieter Seebach
on the occasion of his 60th birthday
The reasons why relationship between D and p in the Hammett equation [Eq. (1)][’] has been fairly well applicable since
1935 to several thousand heterolytic reactions of substituted
benzene derivatives are by no means obvious. In the Hammett
[*] Prof. Dr. R. Glaser, Dr. C. 3. Horan
Department of Chemistry
University of Missouri-Columbia
Columbia, Missouri 65211 (USA)
Fax: Int. code +(573)882-2754
e-mail : chemrg@showme.missouri edu
Prof. Dr. H. Zollinger
Technisch-chemisches Laboratorium der Eidgenossische Technische Hochschule
Universitatstrasse 16, CH-8092 Zurich (Switzerland)
Fax: Int. code +(1)632-1072
r * ] Presented in part at the Gordon Conference on Electron Distribution and
Chemical Bonding, Plymouth State College, Plymouth, NH, USA, July 2-7,
1995. and at the 30th Midwest Theoretical Chemistry Conference, University
of Illinois, Urbana-Champaign, IL, USA, May 22-24, 1997.
equation, the constants D and p represent a combination of field
(inductive) and resonance effects (mesomeric) . One can therefore conclude that in all of these reactions both effects influence
the reactivity in the same direction and to the same relative
extent. This is indeed the case if one evaluates the same kinetic
data with a dual substituent parameter (DSP) treatment, as, for
example, developed by Taft and co-workers [Eq. (2); subscripts
F and R indicate field and resonance effect contributions, respectively, to reaction rate constants k, of X-substituted benzene derivatives relative to that of the unsubstituted compounds
(k,)].I2] Effects of electronic substituent can be classified[3a]into
those that are associated with the substituent’s polarity (Zo,F,
n,, nF) and those that are assigned to the substituent’s ability to
transfer charge (R,on).[3b1 This classification relates the substituent constants oF and oRin Equation(2) to polarity and
charge-transfer factors, as indicated in Equation (3).
= (polarity)p, +(charge transfer)pR
The substituent constants in the Hammett equation are assumed to be independent of the reaction.14] Dual substituent
parameter treatments can thus be regarded as a necessary consequence of the two classes of intrinsic substituent effects. Experience shows that in the large majority of cases the ratio pR/pF=
1z 1. We estimate that values of 2 larger than 1.1 or smaller than
0.9 (but still positive) are present in fewer than 10% of all
equilibria and rates for which a Hammett relationship was tested. This result seems surprising, as the field and resonance effects are, in principle, considered to be independent of each
other. There are, however, sixteen reactions with opposite signs
for pF and pR,that is, iis negative.[’] Examples are dediazoniations of benzenediazonium ions in water, 1,2-dichloromethane,
and trifluoroethanol; these reactions all show pF< - 3.5,
PR’ + 2.2, and lpFl 1pRI.
Due to our interest in the structure of benzenediazonium
ions,161the nature of C-N dative bonding,”] and its dediazoniations,I5- *I we investigated the theoretical basis for the opposing influences of the field and resonance effects on dediazoniation of para-substituted benzenediazonium ions para-X-C,H,N l ( l a , X = H; 1 b, X = NH,; l c , X = NO,) to the respective
para-substituted phenyl cations 2a-c (see Figure 1). Zollinger
interpreted the opposite signs of the reaction constants pF and
pR by proposing that the cleavage of the CT bond between the
N, lone pair and the sp2 LUMO of 2 is slowed by inductively
withdrawing substituents and should give rise to a substantial
negative field reaction constant pF. If N-C CT bonding is reinforced by C + N n backbonding, a positive reaction constant pR
is plausible, since dissociation leads to an increase in K density
on the phenyl fragment and brings K-electron density closer to
the substituent. While this interpretation cannot be demonstrated experimentally, it is possible to examine it with electronic structure methods. We carried out electron-density analyses of the unimolecular dissociations 1-2 + N, (X = H, NH,,
Our objectives here are to show that the reaction constants of
the dediazoniation reactions are consistent with the hypothesis
of combined C t N CT dative and C-N 7c backdative bonding.
Furthermore, we want to learn about the mechanisms by which
two important substituents affect electronic structure. The electron-density analysis is based on the topological features of total
electron densities, which are observable in the quantum me-
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aldehyde, oxidation, anaerobic, ketone, coppel, alcohol, catalyzed
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