A convenient and highly productive aminohydroxylation protocol employing an osmium-diamine catalyst

Article abstract of DOI:10.1002/adsc.200606054

In situ generated osmium-diamine chelates from 2,3-diaminopropionic acid or diaminosuccinic acid represent efficient catalysts for the highly productive aminohydroxylation of alkenes. The reaction can be employed with various osmium salts and successful c

Full text of DOI:10.1002/adsc.200606054

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DOI: 10.1002/adsc.200606054
A Convenient and Highly Productive Aminohydroxylation Proto-
col Employing an Osmium-Diamine Catalyst
Kilian Muñiz,a,c,* Iriux Almodovar,c,d Jan Streuff,a,c and Martin Niegerb
a
Institut de Chimie, Université Louis Pasteur, 4 rue Blaise Pascal, 67070 Strasbourg Cedex, France
Fax: (+33)-3-9024-1526; e-mail: muniz@chimie.u-strasbg.fr
Institut für Anorganische Chemie der Universität Bonn, Gerhard-Domagk-Str. 1, 53121 Bonn, Germany
Kekulé-Institut für Organische Chemie und Biochemie, Gerhard-Domagk-Str. 1, 53121 Bonn, Germany
Departamento de Química Orgánica y Físicoquímica, Facultad de Ciencias Químicas y Farmaceúticas, Universidad de
b
c
d
Chile, casilla 233, Santiago 1, Chile
Received: February 15, 2006; Accepted: July 19, 2006
Supporting information for this article is available on the WWW under http://asc.wiley-vch.de/home/.
Abstract: In situ generated osmium-diamine che-
lates from 2,3-diaminopropionic acid or diamino-
succinic acid represent efficient catalysts for the
highly productive aminohydroxylation of alkenes.
The reaction can be employed with various osmium
salts and successful catalyst recycling was demon-
strated for a representative example. The catalyst
design derives from the general structural features
of recently investigated osmium complexes from
alkene diamination reactions.
Keywords: amino alcohols; aminohydroxylation; di-
amines; homogeneous catalysis; osmium
Figure 1. Osmaimidazolidine product from alkene diamina-
tion and stability towards stoichiometric re-oxidation.
Recently, we have intensively investigated the diami- osmium catalysts from suitable osmium precursors
nation of alkenes employing preformed bis- and tris- such as OsCl3, K
2ACHTRE[UNG OsO2(OH)4] or OsO4 by complexa-
(tert-butylimido)osmium
AHCTREUNG
agents induce a completely chemoselective reaction in A, Figure 2). Tosylamides have recently emerged as a
favour of diamination[2] and lead to monomeric successful leitmotif in ligand design undergoing rapid
osmium-diamine chelates with an unprecedented sta- coordination to transition metal centres. The sulfonyl
bility (Figure 1).[3] The inherent properties of these group enhances the acidity of the N H bond, but
À
products prompted us to examine whether or not does not effect the desired sp3-hybridisation at nitro-
such compounds themselves could act as catalyst pre- gen.[6–8]
cursors for oxidation chemistry. However, the ex-
The choice of the free carboxylic acid motif was
tremely low tendency of the osma(VI)imidazolidine made since recent work by Sharpless and Fokin had
group to undergo oxidation at the central Os atom – shown that some special substrate classes exist such as
a consequence of electronic saturation due to the acrylic acids and their amide derivatives, respectively.
basic alkyl substituents at the neighbouring nitrogens These substrates do not react under standard AD and
– has so far prevented their use as efficient oxidation AA conditions.[9] Instead, oxidation of these com-
catalysts for alkene functionalisation.[4,5] In order to pounds occurs exclusively in a competing secondary
overcome this problem, the incorporation of amino catalytic cycle which is independent of the usual Cin-
groups with lower lone pair donating ability was envi- chona alkaloid ligands. Consequently, certain carbox-
sioned.
ylic acids bearing 2,3-diol or aminohydroxy function-
To this end, it was decided to replace the rather alities were introduced as bidentate ligands for the ef-
basic tert-alkyl substituents at nitrogen and construct ficient oxidation of other olefins.[10]
Adv. Synth. Catal. 2006, 348, 1831 – 1835
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Kilian Muñiz et al.
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Table 1. Aminohydroxylation of symmetrical olefins.
Figure 2. Diaminocarboxylic acids for in situ formation of
osmaimidazolidine catalysts A.
Conversion of commercially available diaminopro-
pionic acid into its N,N’-bistosylated derivative 1 em-
ploying a literature procedure[11] led to a first ligand
following the concept outlined in Figure 2. In a simi-
lar manner, ligand 2 was synthesised from the known
compound 3[12] followed by a sequence of tosylation
(X-ray analytical confirmation of conformation for in-
termediate 4)[13] and ester hydrolysis.[14]
[a]
[b]
Precipitated material at 100% olefin conversion.
With 0.2 mol% catalyst loading, 48 h reaction time.
Active catalysts were then prepared in situ by com-
plexation of preformed ligands 1 and 2 displaying free hexene was successfully carried out for five consecu-
carboxylic acid units to OsO4, K2A[O2Os(OH)4] and tive runs (82 to 78% chemical yield, Figure 3).
OsCl3, three commercially available Os sources which This result represents a rare example for the re-use
CTHREUNG
were found to be equally successful for this pur- of osmium-based oxidation catalysts. Thus far, there
pose.[15] Due to the easier handling, osmium trichlor- have been reports on the immobilisation of chiral
ide and the osmate salt were used in subsequent reac- Cinchona alkaloid ligands,[16] however, these ap-
tions. Thus, with diamino ligands 1 or 2 (1.5 equivs., proaches require the subsequent addition of osmium
relative to Os) and in the presence of one equivalent amounts. Elegant concepts as those from Kobayashi
of chloramine-T as terminal oxidant, clean aminohy- and Jacobs use encapsulated[17] or heterogeneously
droxylation of a variety of olefins was accomplished bound[18] osmium tetroxide for repeated dihydroxyla-
with complete conversion. For example, cyclohexene, tion reactions. However, application in aminohydrox-
dimethyl fumarate, stilbenes and 5-decene underwent ylation remains to be investigated.
aminohydroxylation in high yields upon precipitation
Finally, the aminohydroxylation protocol was em-
(Table 1). The reaction still worked well with a cata- ployed for non-symmetrical olefins (Table 2). Here,
lyst loading of as low as 0.2 mol%. Even on the basis oxidation of methyl, tert-butyl and isopropyl cinna-
of its rather small ligand scaffold, enantiopure 1 in- mate proceeded smoothly within 14 h with quantita-
duced a 32% ee in the asymmetric aminohydroxyla- tive conversion to give the corresponding amino alco-
tion of cyclohexene.
hols in high isolated yield after precipitation. The ob-
In most of these cases, the products were isolated tained regioisomeric ratios were found to be inde-
by filtration leaving the remaining filtrate with the pendent of the use of ligand 1 or 2. Phenyl cinnamate
osmium catalyst for potential use in a subsequent fur- gave an essentially 1:1-mixture of regioisomers. Appa-
ther aminohydroxylation. In order to prove the feasi- rently, the influence of the phenyl ester on regioselec-
bility of such catalyst re-use, the oxidation of cyclo- tivity from the related first cycle aminohydroxylation
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Aminohydroxylation Protocol Employing an Osmium-Diamine Catalyst
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Table 2. Aminohydroxylation of unsymmetrical olefins.
Figure 3. Re-use of an osmium catalyst for consecutive ami-
nohydroxylation of cyclohexene.
[a]
with acetamide-derived nitrenes does not apply fa-
vourably in the present case. b-Methylstyrene gave
high yields and moderate regioselectivities as well. a-
Methylstyrene led to the selective formation of a re-
gioisomeric product due to steric control with the hy-
Determined from the crude 1H NMR.
Combined yield of both regioisomers after precipitation
(at 100% alkene conversion).
[b]
droxy group being placed at the quaternary stereocen- ing bistosylated diamino acids as ligands. First, on the
tre for reactions with both ligands 1 and 2. basis of the unprecedented stability of monomeric os-
The postulated catalytic cycle for the observed maimidazolidines, all the osmium should be bound ex-
highly productive aminohydroxylation is depicted in clusively to the diamine ligand and no ligand scram-
Figure 4. It is initiated by formation of osma(VI)imi- bling to yield bisCAHTRE(UNG diamino) complexes can take place.
dazolidine B from free 1 or 2 and an osmium source This is of major importance since ligand exchange has
in agreement with the expected general catalyst struc- been observed for related glycolate and azaglycolate
ture A. This undergoes oxidation to form the actual complexes[4,5,20] thereby releasing uncomplexed
osma
nohydroxylation gives the intermediate D which upon
hydrolytic cleavage affords the free amino alcohol reoxidation to Os
ACHTREUNG
AHCTREUNG
product and regenerates catalyst precursor B. This catalyst C from B. Therefore, the catalyst system de-
final step requires preferential hydrolysis of the aza- scribed herein consists of a delicate balance between
glycolate structure over the imidazolidine core which the inherent properties of osmaimidazolidines: while
is in agreement with the observed relative stabilities the diamino entity ensures hydrolytic stability of the
of related osmium complexes from stoichiometric re- Os-diamine chelate, the tosyl substituents ensure the
actions.[19] Both the five-membered ring chelate and reoxidation of the catalytically prerequisite Os
ACHTREUNG
the free carboxylate are prerequisites for achievement centre.[21]
of high reactivity and catalyst stability. Application of
N,N’-bistosylethylenediamine and 2,4-bis(tosylamino)- situ generated chiral osmaimidazolidines as homoge-
butanoic acid as ligands led to complete loss of cata- neous oxidation catalysts. Concerning yields, catalyst
lyst activity.
loading and regioselectivities, our results compare
Compared with the previous diol or amino alcohol- well with the ones from former azaglycolate cata-
based ligands,[10] we postulate two differences regard- lysts.[9,10] Chemoselectivities are excellent for this pro-
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Kilian Muñiz et al.
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(300 MHz, CDCl3): d=7.69 (d, J=8.34 Hz, 2H), 7.28 (d, J=
8.34 Hz, 2H), 5.50 (d, J=8.40 Hz, 1H), 4.36 (d, J=8.40 Hz,
2H), 3.95–4.15 (m, 2H), 2.41 (s, 3H), 1.16 (t, J=7.13 Hz,
3H); 13C NMR (75 MHz, CDCl3): d=167.7, 149.7, 144.0,
136.2, 130.0, 129.7, 127.4, 63.0, 57.8, 21.5, 13.8; MS (EI, eV):
m/z (%)=512.1 (0.25% [M+]), 439.1 (0.75%), 357.1 (5%)
256.1 (100%), 155,0 (100%), 102.0 (80%). IR (KBr): n=
3405, 2970, 2909, 2366, 2355, 1451, 1230, 1100 cmÀ1; HR-MS:
m/z=512.1284, calcd. for C22H28N2O8S2: 512.1287 gmolÀ1.
2,3-Bis(tosylamino)succinic Acid (2)
Diethyl [2,3-bis(tosylamino)]succinate (1.00 g, 19.5 mmol)
was dissolved in a 2M aqueous LiOH and stirred for 40 h at
room temperature. The solution was filtered through cotton
wool and made acidic by addition of 3M HCl solution. Plac-
ing the resulting solution in the freezer overnight resulted in
precipitation of the title compound in form of a white solid;
yield: 508 mg (11.1 mmol, 57%). 1H NMR (300 MHz,
DMSO-d6): d=2.28 (s, 6H), 4.22 (s, 2H), 7.31 (d, J=8.5 Hz,
4H), 7.69 (d, J=8.5 Hz, 4H), 13.04 (brs, 2H); 13C NMR
(75 MHz, DMSO-d6): d=21.40, 58.02, 127.17, 129.69, 138.29,
143.13, 169.26.
General Experimental Procedure for
Aminohydroxylation in the Presence of N,N’-
Bistosyldiaminopropionic Acid or 2,3-
Bis(tosylamino)succinic Acid
Figure 4. Postulated catalytic cycle for aminohydroxylation.
Ligand 1, osmate source and geometry of intermediate D
shown arbitrarily.
To a solution of of the ligand (1 or 2, 0.15 mmol) and potas-
sium osmate (36.8 mg, 0.1 mmol) in 6 mL of water/tert-butyl
alcohol (1/1, v/v) at room temperature was added potassium
carbonate (41.5 mg, 0.3 mmol) and the resulting mixture stir-
red at room temperature for 15 min. Chloramine-T (1.55 g,
5.5 mmol) was then added in one portion, at which point the
reaction mixture turned bright yellow. The olefin (5.0 mmol)
was added in one portion and the resulting mixture stirred
for the periods given in Table 1 and Table 2. [For reaction
times longer than 10 h, the pH is adjusted to 8 after this
period. Reactions employing osmium trichloride as catalyst
source were carried out with an initial addition of 125 mg of
potassium carbonate.]
Generally, the products crystallised from the reaction mix-
ture and were isolated by simple filtration. If desired, the
crude reaction mixtures can be extracted with dichlorome-
thane. Column chromatography of the crude product with
solvent mixtures of hexanes/ethyl acetate gives analytically
pure samples.
cess with no diol formation ever being observed.[22]
While regioselectivities and enantiomeric induction
for this second cycle catalysis is still much lower than
for the established Cinchona alkaloid based AA pro-
tocol,[6] the present diaminocarboxylic acid motif
offers room for future ligand optimisation. Investiga-
tion on related structures based on different diamino
entities are currently under investigation.
Experimental Section
Diethyl [2,3-Bis(tosylamino)]succinate (4)
Racemic diethyl [2,3-bis(diphenylmethylene-amino)] succi-
nate[12] (2.66 g, 5 mmol) was dissolved in commercially avail-
able methanolic HCl solution (30 mmol, 6 equivs.) and stir-
red for 24 h at room temperature. The solvent was removed
under reduced pressure and the remaining oily residue
taken up in two portions of absolute dichloromethane
(20 mL each) to remove remaining acid. All solvents were
removed under reduced pressure and the residue was dis-
solved in absolute dichloromethane (40 mL) followed by ad-
dition of triethylamine (10 mL) and toluenesulfonyl chloride
(3.42 g, 18 mmol, 3.6 equivs.) and stirring at room tempera-
ture overnight. It was worked-up by addition of water
(100 mL) and extraction with dichloromethane. The com-
bined organic phases were separated, dried with MgSO4 and
evaporated to dryness under reduced pressure. Column
chromatography (silica gel, hexanes/ethyl acetate, 75/25, v/v)
gave a white product which was crystallised from ethyl ace-
Supporting Information
Detailed experimental procedures, synthesis of ligands 1 and
2, product characterisation and data on X-ray analysis.
Acknowledgements
This work was supported by the Deutsche Forschungsgemein-
schaft (MU 1805/2–1), the Deutscher Akademischer Aus-
tausch-Dienst (grant to I. A.), the Fonds der Chemischen In-
dustrie and the Otto-Röhm-Gedächtnisstiftung. The authors
are grateful to Prof. Dr. K. H. Dötz for his support and inter-
1
tate to give colourless prisms; yield: 2.15 g (84%). H NMR
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Aminohydroxylation Protocol Employing an Osmium-Diamine Catalyst
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est, and to Stefan Kürpig for initial work on the synthesis of
ligand 2.
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[21] Initial screening experiments (included as Table S2 in
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