Synthesis and application in enantioselective hydrogenation of new free and chromium complexed aminophosphine-phosphinite ligands

Article abstract of DOI:10.1016/S0957-4166(97)00642-3

A straightforward synthesis of new free and Cr(CO)₃ complexed AMPP ligands (4-7) is described starting from (S)-indoline-2-carboxylic acid. The ligands were applied successfully in the asymmetric hydrogenation of α-functionalized ketones i.e. a ketolactone 8, a ketoamide 9 and an aminoketone 10 leading to the corresponding optically active alcohols in 99, 97, and 99% ee respectively.

Full text of DOI:10.1016/S0957-4166(97)00642-3

Pergamon
Tetrahedron: Asymmetry 9 (1998) 193–196
Synthesis and application in enantioselective hydrogenation of
new free and chromium complexed aminophosphine–phosphinite
ligands
a
a
b
b
a
Corinne Pasquier, Said Naili, Lydie Pelinski, Jacques Brocard, André Mortreux and
a,∗
Francine Agbossou
a
Laboratoire de Catalyse Hétérogène et Homogène, URA CNRS 402, Groupe de Chimie Organique Appliquée, Ecole
Nationale Supérieure de Chimie de Lille, B.P. 108, 59652 Villeneuve d’Ascq Cédex, France
Laboratoire de Catalyse Hétérogène et Homogène, URA CNRS 402, Groupe de Synthèse Organométallique, Université des
Sciences et Technologies de Lille, 59655 Villeneuve d’Ascq Cédex, France
b
Received 25 November 1997; accepted 23 December 1997
Abstract
A straightforward synthesis of new free and Cr(CO)3 complexed AMPP ligands (4–7) is described starting
from (S)-indoline-2-carboxylic acid. The ligands were applied successfully in the asymmetric hydrogenation of
α-functionalized ketones i.e. a ketolactone 8, a ketoamide 9 and an aminoketone 10 leading to the corresponding
optically active alcohols in 99, 97, and 99% ee respectively. © 1998 Elsevier Science Ltd. All rights reserved.
There has been great interest devoted to asymmetric synthesis catalyzed by optically active transition
metal complexes and the access to chiral bisphosphines which are capable of bringing very high
enantioselectivities plays a critical role in the development of homogeneous asymmetric catalytic
1
processes. On the other hand, arene–Cr(CO) complexes have frequently proven their value for organic
3
2
synthesis. Further, due to their plane of chirality, Cr(CO) complexes of unsymmetrically ortho-
3
3
disubstituted arenes have become valuable chiral reagents in stereoselective synthesis. Such complexes,
presenting a planar metallocene chirality, have found applications as ligands when transformed into
phosphines in catalytic processes. In particular, ferrocenyl derivatives exhibiting this type of chirality
4
have been the most studied and used in asymmetric catalysis. Despite their interesting electronic and
6
5
steric properties, chiral (η -arene)–chromium moieties have been less studied as chiral auxiliaries.
We have an ongoing interest in the synthesis and application in asymmetric catalysis of both chromium
6
7
complexes and aminophosphine–phosphinite diphosphines (AMPP). Thus, we set out to synthesise
and evaluate new AMPP ligands possessing a benzene coordinated with Cr(CO) with the hope of
3
combining the unique properties provided by both classes of compounds. In this communication, we
∗
Corresponding author.
0957-4166/98/$19.00 © 1998 Elsevier Science Ltd. All rights reserved.
PII: S0957-4166(97)00642-3

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C. Pasquier et al. / Tetrahedron: Asymmetry 9 (1998) 193–196
report the synthesis of novel homochiral AMPP ligands derived from (S)-indoline-2-carboxylic acid 1
and of the corresponding diphosphines coordinated with Cr(CO) as well as their use in enantioselective
3
hydrogenation.
As shown in Scheme 1, (S)-2-hydroxymethyl-indoline 2 was easily obtained through standard
procedures starting from the corresponding acid. Thus, 1 was first reduced in the presence of bo-
8
rane–methylsulfide complex and the resulting oxazaborolidine was hydrolysed in situ with sodium
hydroxide leading to the β-aminoalcohol 2 as a white powder in ca. 100% overall yield after workup.9
Scheme 1.
The aminoalcohol 2 was then converted into two diastereomers bearing the Cr(CO) moiety co-
3
ordinated to each enantioface of the indoline ring. However, in order to separate the two Cr(CO)3
complexes, a prior substitution of the primary alcohol was necessary. Thus, 2 was reacted first with t-
butyldimethylsilyl chloride in dichloromethane giving the silylether. Then, chromium complexation took
place in the presence of Cr(CO) in THF providing a mixture of the syn and anti diastereomers (24:76
6
ratio) which were isolated as yellow powders in 70% global yield after a silica gel chromatographic
workup. Finally, in separate experiments, the syn and anti isomers were treated with nBu NF to generate
4
syn-3 and anti-3 aminoalcohols subsequently isolated in quantitative yield (Scheme 1).9
The three precursors 2, syn-3, and anti-3 were next converted to the corresponding diphosphines.
7
The general method applied for the synthesis of AMPP ligands (ClPR , NEt ) was employed
2
3
with success leading after workup to (S)-Ph,Ph–IndoNOP 4, (R,2S)-Cr(CO) –Ph,Ph–IndoNOP 5,
3
(
S)-Cp,Cp–IndoNOP 6 and (S,2S)-Cr(CO) –Cp,Cp–IndoNOP 7 in 40–80% unoptimized yields
3
10
(Scheme 2). The (R,2S)-Cr(CO) –Cp,Cp–IndoNOP AMPP could be obtained in some extent following
3
an identical protocol. However, (S,2S)-Cr(CO) –Ph,Ph–IndoNOP could not be prepared by this route,
3
7
a
(
S,2S)-Cr(CO) –Ph–IndoNHOP, the intermediate amino-phosphinite, being the product formed as
assayed by P NMR. We wondered whether the use of a strong base might enable the resulting amide
3
31
to undergo the expected addition to the chlorophosphine. However, a reaction of syn-3 with either NaH
or nBuLi followed by the reaction with ClPPh gave only the amino-phosphinite.
2
Scheme 2.
The new AMPP derivatives were then transformed onto catalyst precursors. Based on our previous
7
studies, we chose to synthesize in situ [Rh{AMPP}Cl] and [Rh{AMPP}(OCOCF )] species.
2
3 2
The complexes were applied in the asymmetric hydrogenation of dihydro-4,4-dimethyl-2,3-
furandione 8, N-benzylbenzoylformamide 9, and 2-(N,N-dimethyl)aminoacetophenone hydrochloride
10 (Scheme 3). Selected results as well as some earlier data are summarized in Table 1.
The hydrogenations proceeded at either room temperature or 50°C under an initial hydrogen pressure
of 1 or 50 bar, the chiral alcohols being produced in high yields. The reaction promoted by the rhodium

C. Pasquier et al. / Tetrahedron: Asymmetry 9 (1998) 193–196
195
Scheme 3.
Table 1
a
Asymmetric hydrogenation of α-functionalized ketones
catalyst bearing the phenyl substituted AMPP 4 needed drastic conditions for a rather low rate and
moderate enantioselectivity (50% ee) (run 2). In contrast, cyclopentyl substituted AMPPs 6 and 7
efficiently control the selectivity of the hydrogenation (runs 3, 4, 9 and 11). Indeed, the behaviour of
phenyl versus cycloalkyl substituted AMPPs during the Rh-based hydrogenation of ketones has been
7
established already in earlier work. Importantly, the new chiral backbone introduced here brought
about an interesting enhancement of selectivity compared to the more efficient AMPPs reported so far
(compare runs 3 and 4 with 1, 6–9 with 5, and 11 with 10). Moreover, we hoped that ligands with a
Cr(CO) –indoline chiral core might give improved enantioselectivities with respect to the uncomplexed
3
parent diphosphine. As a matter of fact, there was no difference between 6 and 7 for the hydrogenation
of 8, the enantioselectivity being already very high (ee >99%). However, a significant ee increase
was obtained when applying 7 instead of 6 in the hydrogenation of 9 (97% versus 91% ee, run 9
versus 7). Furthermore, the non-chiral ligand (Cl or TFA) also contributes to the selectivity of the
hydrogenation of 9. In this context, it is instructive to contrast the efficiency of Rh–Cl precursors with
that of Rh–TFA during the catalysis. As shown in Table 1, the chromium complexed ligand 7 allowed
a 6% ee enhancement when associated with the Rh–Cl moieties (compare run 9 with 8). Thus a total
increase of 13% ee was accessible in combining the chromium derivative 7 with the Rh–Cl complex (run
9
versus 6). Surprisingly, the hydrogenation of 8 carried out in the presence of ligand 5 gave <1% ee.13
Finally, we found that the new ligands reported here allowed the hydrogenation of the three substrates
–10 with the highest enantioselectivities reported so far. Investigations for improved enantioselectivities
through the syntheses of new AMPPs is still in progress and will be reported in due course.
8

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C. Pasquier et al. / Tetrahedron: Asymmetry 9 (1998) 193–196
Acknowledgements
We are grateful to Dr. Jean-François Carpentier for helpful discussions. We thank the ‘Ministère de la
Recherche et de la Technologie’ and the CNRS for their financial support.
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8
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1
9. 2: H NMR (300 MHz, CDCl
3
): δ 7.1 (d, J=7.3 Hz, 1H), 7.0 (t, J=7.6 Hz, 1H), 6.7 (d, J=7.3 Hz, 1H), 6.65 (d, J=7.6 Hz,
=10.7 Hz, J =3.5 Hz, 1H), 3.6 (dd, J =10.7 Hz, J =6.3 Hz, 1H), 3.1 (dd, J =15.9 Hz, J =9.0
=15.9 Hz, J ): δ 150.5, 128.9, 127.5, 124.9, 119.3, 110.1,
=7.9 Hz, 1H); 13C NMR (75.5 MHz, CDCl
): δ 5.6 (d, J=5.6 Hz, 1H), 5.4 (s, 1H), 5.0 (d, J=6.4 Hz, 1H), 4.8
1
H), 4.0 (m, 1H), 3.7 (dd, J
Hz, 1H), 2.8 (dd, J
5.2, 60.3, 32.1, 30.6. syn-3: H NMR (300 MHz, CDCl
1
2
1
2
1
2
1
2
3
1
6
(
3
1
3
s, 1H), 4.1 (m, 2H), 3.6 (d, J=7.3 Hz, 1H), 3.1 (dd, J
1
2
=10.3 Hz, J =14.4 Hz, 1H), 2.6 (d, J=14.4 Hz, 1H); C NMR (75.5
1
MHz, CDCl
3
): δ 237.4, 135.3, 98.7, 97.0, 96.0, 86.5, 76.2, 65.3, 60.5. anti-3: H NMR (300 MHz, CDCl
3
): δ 5.6 (d, J=5.3
1
3
Hz, 1H), 5.4 (s, 1H), 5.0 (d, J=5.5 Hz, 1H), 4.8 (s, 1H), 4.2 (m, 2H), 3.8 (m, 2H), 3.6 (s, 1H), 2.8 (d, J=8.7 Hz, 1H);
NMR (75.5 MHz, CDCl ): δ 234.6, 133.1, 98.3, 94.6, 93.1, 84.5, 74.0, 63.9, 60.6, 30.6.
0. 31P{ H} NMR data at 121 MHz (ppm, CDCl
) 4: 114.2 (s, OPPh ), 41.6 (s, NPPh ); 5: 116.9 (s, OPPh
: 145.9 (s, OPCp ), 63 (s, NPCp ); 7: 146 (s, OPCp ), 67.3 (s, NPCp ).
C
3
1
1
3
2
2
2 2
), 43.1 (s, NPPh
);
6
2
2
2
2
1
1
1
1. Roucoux, A.; Agbossou, F.; Mortreux, A.; Petit, F. Tetrahedron: Asymmetry 1993, 4, 2279.
2. Devocelle, M.; Agbossou, F.; Mortreux, A. Synlett 1997, in press.
3. It would be premature to form conclusions regarding the relative effect on the selectivity of the chromium complexation
without extending the study to the other diastereomer and thus searching for the accessibility to the latter.