Exploring the nickel-catalyzed oxidation of alkenes: A diamination by sulfamide transfer

Article abstract of DOI:10.1002/anie.200702160

(Chemical Equation Presented) Nickel can oxidize, too! Nickel (II) salts such as nickel chloride and nickel acetylacetonate catalyze the intramolecular diamination of alkenes with urea and guanidine derivatives as well as sulfamides as nitrogen sources. T

Full text of DOI:10.1002/anie.200702160

Angewandte
Chemie
DOI: 10.1002/anie.200702160
Oxidation Catalysis with Nickel
Exploring the Nickel-Catalyzed Oxidation of Alkenes: A Diamination
by Sulfamide Transfer**
Kilian Muæiz,* Jan Streuff, Claas H. Hövelmann, and Ana Nfflæez
Nickel catalysts play an important role in catalytic processes
under homogeneous conditions.[1] Their development is
largely related to the fundamental work on organonickel
structure chemistry by Wilke.[2] These advances led to the
2
3
À
establishment of seminal reactions such as sp and sp C C
cross-coupling reactions,[3,4] enantioselective hydrovinyla-
tion,[5] cyclization and isomerization reactions,[6,7] as well as
important industrial processes such as the Shell higher olefin
process (SHOP).[8]
Herein, we describe the (to our knowledge) first applica-
tion of nickel catalysts to a homogeneous oxidation of
alkenes, namely direct diamination.[9] We consider the devel-
opment of vicinal diamination of alkenes to be an important
research target,[10] since it closes a methodological gap in the
synthesis of this class of compounds.[11] For the development
of useful synthetic transformations, the appropriate choice of
protecting groups in the nitrogen source plays a dominant
role.
To this end, we considered sulfamide groups particularly
attractive,[12,13] since they allow for both a convenient
liberation of the free diamine and a differentiation between
the two nitrogen atoms. Palladium-catalyzed reactions with
the sulfamide precursor 1a[14] did not lead to the formation of
the desired diamination product 2a, but gave exclusively the
aminoacetoxylation product 3 (Scheme 1).[15] The ratio of 2a
to 3 could be completely inverted in favor of diamination
when the palladium(II) catalysts were replaced by nickel(II)
salts. A first reaction in the presence of 10 mol% nickel(II)
chloride hexahydrate provided diamine 2a in an encouraging
38% yield. This new process required careful optimization of
the reaction conditions. Investigation of different solvents and
bases revealed that DMF and two equivalents of sodium
acetate represent the optimum combination (Table 1). A
comparison of various nickel salts showed that NiCl2 and
[Ni(acac)2] give the best results. These catalysts do not
deactivate over time and are still active after 54 h reaction
time. Finally, complete conversion was achieved with anhy-
Scheme 1. Catalyst-dependent oxidation of sulfamide 1a.
Table 1: Optimization of the nickel-catalyzed transformation of 1a into
2a.[a]
Catalyst source
T [8C]
t [h]
Yield [%][b]
no NiII salt
NiSO4
NiCl2·6H2O
NiCl2·6H2O
NiCl2
40
40
25
25
40
40
40
40
40
18
18
18
54
18
18
18
18
18
0[c]
<10
38
71
100 (92[e])
[(dppe)NiCl2][f]
[(bipy)NiCl2][f]
[Ni(acac)2][d, f]
[Ni(acac)2]
72
80
23
100 (92[e])
[a] General conditions: 10 mol% catalyst, 2 equiv PhI(OAc)2, 2 equiv
NaOAc, DMF. [b] Conversion according to 1H NMR spectroscopy.
[c] Reisolated starting material. [d] 1.1 equiv PhI(OAc)2. [e] Yield of
isolated product. [f] dppe=1,2-bis(diphenylphosphanyl)ethane, bipy=
bipyridine, acac=acetylacetonate.
drous precursor NiCl2 or [Ni(acac)2] and two equivalents of
oxidant under inert conditions at 408C.
The oxidation is even catalyzed by unligated nickel(II)
salts, but addition of common chelating ligands such as
bipyridine gives stable catalysts as well. Control experiments
monitored by 31P NMR spectroscopy revealed that [(dppe)-
NiCl2] readily loses the diphosphine ligand under oxidative
conditions to generate a free nickel salt and phosphine oxide.
As a consequence, NiCl2 or [Ni(acac)2] were employed as
catalysts for subsequent investigation of the intramolecular
diamination of sulfamides (Scheme 2).
[*] Prof. Dr. K. Muæiz, Dipl.-Chem. J. Streuff,
Dipl.-Chem. C. H. Hövelmann, Dr. A. Nfflæez
UniversitØ Louis Pasteur
Institut de Chimie, UMR 7177
4, rue Blaise Pascal, 67070 Strasbourg (France)
E-mail: muniz@chimie.u-strasbg.fr
All reactions proceeded with complete selectivity, and no
products other than the cyclic sulfamides were observed. A
range of substrates with different substituents was tolerated,
which includes the styrene derivatives 1j and k. Chiral
compounds 1l,m were transformed into the two correspond-
ing diastereoisomeric products. The novel cyclization precur-
sor 1n underwent clean oxidation to yield an equimolar
Homepage: http://www-chimie.u-strasbg.fr/~lchsm/
[**] This workwas generously supported by the Fonds der Chemischen
Industrie and the Agence Nationale de la Recherche. The authors
thankProf. J. Gonzµlez and E. Campos (Oviedo) for a sample of
compound 6b.
Supporting information for this article is available on the WWW
under http://www.angewandte.org or from the author.
Angew. Chem. Int. Ed. 2007, 46, 7125 –7127
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Communications
Scheme 3. Deprotection to the free diamine 5. TFA=trifluoroacetic
acid.
cleavage with methoxide for 2a, hydrogenolysis in case of 2b,
or protonolysis for 2c, yielding free sulfamide 4. Direct
treatment with lithium aluminium hydride furnishes free
aminomethyl pyrrolidine 5, which is also directly accessible
from 2a. These sequences illustrate that sulfamides can be
used advantageously in diamination reactions.
Urea groups[14] are cyclized equally well under the
conditions of nickel-catalyzed diamination. For example,
diamination of the cyclohexyl derivative 6a to 7a proceeds
with complete selectivity (Scheme 4), and the related guani-
Scheme 4. Nickel-catalyzed diamination of urea and guanidine deriva-
tives. Values in bold refer to the better catalyst. Tos=toluene-4-
sulfonyl.
dine derivative 6b is oxidized cleanly to the corresponding
cyclic derivative 7b. These examples further exemplify the
range of functional groups that are tolerated by the new
nickel-catalyzed intramolecular diamination.
Mechanistic investigation of the exact course of the
reaction is currently underway. We expect that the reaction
proceeds through a stepwise process of aminometalation and
Scheme 2. Nickel-catalyzed diaminations. Given yields are based on
isolated material. All reactions proceed with 100% selectivity in favor
of diamination. Bn=benzyl. [a] Reactions with [Ni(acac)2].
À
C N coupling comparable to the palladium-catalyzed variant
(Scheme 5). These two steps have literature precedence.
Nickel-catalyzed hydroamination is known for polarized
alkenes[17] and butadienes,[18] and has been theoretically
mixture of all four possible stereoisomeric tetraamination
products. A diastereoselective reaction succeeded with the
chiral substrate 1o, which cleanly yielded the prolinyl amine
derivative 2p.
All reactions proceeded at room temperature as well,
albeit at a slower rate (50–80% conversion after 16 h). The
exception is precursor 1b, which gives quantitative product
formation after 18 h at room temperature. The reaction scale
can be varied; an increase to 4.5 g (10 mmol) of 1b in the
presence of 10 mol% Ni catalyst gives quantitative formation
of 2b.
The sulfamide products can be conveniently transformed
into the free diamines (Scheme 3).[16] The removal of the
carbamate groups in 2a–c can be accomplished through basic
Scheme 5. Mechanistic sequence and isolated hydroamination product
8.
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Angewandte
Chemie
predicted for neutral akenes.[19] The isolation of 8 yields
evidence for an initial involvement of aminometalation. This
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[9] Generally, Ni-catalyzed homogeneous oxidation reactions
appear to have been less investigated. For a recent study on an
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J. Org. Chem. 2006, 71, 9291.
[10] K. Muæiz, New J. Chem. 2005, 29, 1371.
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[12] For a diamination with N-alkyl sulfamides in the presence of
excess copper acetate: T. P. Zabawa, D. Kasi, S. R. Chemler, J.
Am. Chem. Soc. 2005, 127, 11250.
[13] Nicolaou et al. described Burgess reagents for stoichiometric
transformation of amino alcohols into the corresponding cyclic
sulfamides: a) K. C. Nicolaou, D. A. Langbottom, S. A. Snyder,
A. Z. Nalbandian, X. H. Huang, Angew. Chem. 2002, 114, 4022;
Angew. Chem. Int. Ed. 2002, 41, 3866; b) K. C. Nicolaou, S. A.
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À
hydroamination product is formed when the C Ni bond of
the intermediate is selectively protonated, in agreement with
the described intermolecular processes; no diamine is
obtained.[20] Related internal alkenes with phenyl or methyl
substituents show low reactivity and varying degrees of
hydroamination, but no diamination. Hence, the overall
reaction is dependent on the nature of the alkene, as only
carbon atoms from terminal alkenes tend to favor the second
amination.
This final step of the suggested mechanism consists of
III
À
oxidative Calkyl N bond formation, presumably via a Ni
intermediate from oxidation with PhI(OAc)2. Such a process
was investigated in detail by Hillhouse and co-workers, who
À
elegantly demonstrated that the Calkyl Ni bond in intra-
molecular aziridine formation can be cleaved under retention
or inversion of the overall configuration.[21] Recently, Caryl
À
N
bond formation from a NiIII complex was also reported.[22,23]
An intermediary involvement of an aminoacetoxylation
product can be excluded, since 3 is not converted to diamine
2a using the nickel-catalysis protocol.
The results presented herein illustrate the first selective
À
C N bond-forming reactions employing nickel oxidation
catalysis. The selectively deuterated alkene 1a forms a
diastereomerically pure diamination product;[16] this result
excludes the involvement of a radical mechanism and suggests
the presence of a clean substitution process in the final step,[24]
in complete agreement with the observations of Hillhouse
and co-workers.
The electronic properties of the involved nitrogen atoms
are of great importance for this second step. While in the case
of palladium the carbamate-substituted nitrogen atom is
unable to compete with acetate, nickel catalysts tolerate a
broader range of nitrogen groups and thereby enable the first
and selective diamination of sulfamides.[25] This broad applic-
ability with respect to sulfamides as well as urea and
guanidine derivatives should allow additional nickel-cata-
lyzed amination reactions. Such approaches are under inves-
tigation.
[14] J. Streuff, C. H. Hövelmann, M. Nieger, K. Muæiz, J. Am. Chem.
Soc. 2005, 127, 14586.
[15] E. J. Alexanian, C. Lee, E. J. Sorensen, J. Am. Chem. Soc. 2005,
127, 7690.
[16] Additional information is included in the Supporting Informa-
tion.
[17] a) L. Fadini, A. Togni, Chem. Commun. 2003, 30; b) W. Zhuang,
R. G. Hazell, K. A. Jørgensen, Chem. Commun. 2001, 1240.
[18] a) J. Pawlas, Y. Nakao, M. Kawatsura, J. F. Hartwig, J. Am.
Chem. Soc. 2002, 124, 3669; b) J. F. Hartwig, Pure Appl. Chem.
2004, 76, 507.
[19] H. M. Senn, P. Blöchl, A. Togni, J. Am. Chem. Soc. 2000, 122,
4098.
[20] This reaction is nickel-catalyzed and requires the presence of
acetate. Reactions without nickel(II) and/or base do not lead to
formation of 8.
[21] a) B. L. Lin, C. R. Clough, G. L. Hillhouse, J. Am. Chem. Soc.
2002, 124, 2890; b) R. Waterman, G. L. Hillhouse, J. Am. Chem.
Soc. 2003, 125, 13350; c) K. Koo, G. L. Hillhouse, Organo-
metallics 1995, 14, 4421; d) K. Koo, G. L. Hillhouse, Organo-
metallics 1996, 15, 2669.
We have extended the scope of nickel-catalyzed reactions
to homogeneous alkene oxidation, which consists of a new,
completely selective intramolecular diamination. This proto-
col is attractive in view of catalyst cost, reaction scope, and
simplicity of subsequent product diversification.
[22] G. Bai, D. W. Stephan, Angew. Chem. 2007, 119, 1888; Angew.
Chem. Int. Ed. 2007, 46, 1856.
[23] For Ni0/NiII-catalyzed Caryl N bond-forming reactions, see: a) S.
À
Ogoshi, H. Ikeda, H. Kurosawa, Angew. Chem. 2007, 119, 5018;
Angew. Chem. Int. Ed. 2007, 46, 4930; b) J. P. Wolfe, S. L.
Buchwald, J. Am. Chem. Soc. 1997, 119, 6054; c) C. Desmarets,
R. Schneider, Y. Fort, Tetrahedron 2001, 57, 7657.
Received: May 16, 2007
Published online: August 10, 2007
[24] At present, we are unable to distinguish between a syn/anti and
an anti/syn process for the two-step diamination. For a discussion
on syn- and anti-aminometalation in related palladium catalysis,
see: A. Minatti, K. Muæiz, Chem. Soc. Rev. 2007, 36, 1142.
[25] Electron-withdrawing substituents at the second sulfamide
nitrogen atom are essential for all reactions. Oxidative decom-
position rather than diamination is observed for less acidic
amides such as benzyl-substituted sulfamides.[12]
Keywords: diamines · homogeneous catalysis · nickel ·
oxidation · sulfamides
.
[1] Modern Organonickel Chemistry (Ed: Y. Tamao), Wiley-VCH,
Weinheim, 2006.
[2] G. Wilke, Angew. Chem. 1988, 100, 189; Angew. Chem. Int. Ed.
Engl. 1988, 27, 185.
[3] Recent review: E.-i. Negishi, Bull. Chem. Soc. Jpn. 2007, 80, 233.
Angew. Chem. Int. Ed. 2007, 46, 7125 –7127
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