Stereoselective synthesis of a new optically active phosphinoacyloxazolidinone via enantioselective hydrogenation

Article abstract of DOI:10.1039/a708223a

The preparation of a new optically active phosphinoacyloxazolidinone, based on the enantioselective hydrogenation of a 4-methylene-N-propionyloxazolidinone in the presence of [(R)-BINAP]Ru(O₂CCF₃)₂ catalyst followed by ste

Full text of DOI:10.1039/a708223a

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Stereoselective synthesis of a new optically active phosphinoacyloxazolidinone
via enantioselective hydrogenation
Pierre Le Gendre, François Je´roˆme, Christian Bruneau* and Pierre H. Dixneuf*†
Laboratoire de Chimie de Coordination et Catalyse, UMR 6509, CNRS-Universite´ de Rennes, Campus de Beaulieu, F-35042
Rennes, France
The
preparation
of
a
new
optically
active
H
HO
phosphinoacyloxazolidinone, based on the enantioselective
hydrogenation of a 4-methylene-N-propionyloxazolidinone
in the presence of [(R)-BINAP]Ru(O2CCF3)2 catalyst fol-
lowed by stereoselective phosphinylation, is reported.
iii
ii
i
O
O
O
O
O
80%
N
N
HN
95%
95%
O
O
O
O
O
O
5
1
(R)-2
4
Chiral diphosphines coordinated to a transition metal centre
have demonstrated their power in asymmetric catalysis.1 More
recently, optically active heterobidentate ligands containing
only one phosphorus group have proved to be very efficient in
a variety of catalytic reactions. Thus, the diphenylphosphino
group attached to a functional group such as an amine,2 an
oxazoline,3 a pyrazole4 or a quinoline5 moiety has led to a
variety of new P–N ligand–metal catalysts which have contri-
buted to the improvement of enantioselectivity in various
catalytic reactions. Other heterobidentate functional phosphine
ligands with an additional coordinating oxygen atom have also
been used successfully in asymmetric catalysis.6–9
Here we report the preparation of a new P–O heterobidentate
ligand of high optical purity based on the synthesis of an
optically active acyloxazolidinone followed by its phosphinyla-
tion. This synthesis does not involve substrates from the natural
chiral pool but is based on two successive selective reactions: (i)
98% ee
Scheme 2 Reagents and conditions: i, NH3, room temp.; ii, EtCOCl,
CH2Cl2 reflux; iii, H2, [(R)-BINAP]Ru(O2CCF3)2, MeOH, 50 °C
of 98%, according to Scheme 2.‡ Compound (R)-2 appears to be
the simplest (R)-enantiomer of the family of Superquats, the
(S)-enantiomer of which has already been prepared from an
amino acid.11
Advantage was taken of the asymmetric induction offered by
chiral acyloxazolidinones to stereoselectively introduce an
electrophile on the acyl group.10,11 We thus attempted to
transform (R)-2 into a functional phosphine of type 3 by
addition of the electrophilic diphenylphosphino group after
deprotonation of the acyl moiety of (R)-2 (Scheme 3).
The N-propionyloxazolidinone (R)-2 (4.3 mmol) was first
deprotonated in THF at 290 °C using LDA (1 equiv.). Then,
chlorodiphenylphosphine (4.3 mmol) was added and the
reaction mixture was kept at 290 °C for 15 h before warming to
room temperature. The resulting phosphinoacyloxazolidinone
(R,R)-3 was purified by chromatography over alumina and
isolated in 87% yield. The 31P NMR spectrum of the crude oil
showed two singlets at d 5.84 and 4.87, indicating the presence
of the two diastereoisomers in the ratio 95:5. This result shows
that the novel transformation of acyloxazolidinones by phosphi-
nylation is stereoselective and that the optically pure
N-propionyloxazolidinone (R)-2 provides efficient asymmetric
induction as already observed for the alkylation with BnBr, of
(S)-2 prepared via a different route.11
the enantioselective hydrogenation of
a
4-methylene-
N-propionyloxazolidin-2-one 1, and (ii) the stereoselective
phosphinylation of the resulting optically active acyloxaz-
olidinone 2, according to Scheme 1.
Whereas optically active acyloxazolidinones are usually
prepared by acylation of oxazolidinones arising from optically
active natural amino acids via multistep syntheses,10,11 we have
shown that it is possible to obtain both enantiomers of the
acyloxazolidinone 2 via enantioselective hydrogenation of the
4-methylene-N-acyloxazolidinone 1 in the presence of a
ruthenium catalyst containing an optically pure diphosphine
ligand.
This functional phosphine is very air-sensitive and it is
preferable to stabilize it as a phosphine–borane adduct. The
addition of BH3·SMe at 280 °C at the end of the reaction
leading to 3 made possible the preparation of the corresponding
phosphine–borane (R,R)-6.§ Chromatography over silica gel
allowed the isolation of only the major diastereoisomer in 47%
yield (100% de).
Cleavage of the N-acyl bond of (R,R)-3 was carried out under
mild conditions in MeOH at room temperature in the presence
of K2CO3 and led to the chiral oxazolidinone auxiliary (R)-8 and
The bubbling of ammonia through an EtOAc solution of the
carbonate 412 at room temperature led to 95% yield of the
hydroxyoxazolidinone 5. The treatment of this cyclic carbamate
with an excess of propionyl chloride in refluxing CH2Cl2 in the
presence of CaCl2 led to the isolation of the acyloxazolidinone
1 (80% yield) in a one pot acylation–dehydration reaction. The
enantioselective hydrogenation of 1 was performed under 10
MPa of H2 in MeOH at 50 °C for 18 h in the presence of 1 mol%
of [(R)-BINAP]Ru(O2CCF3)2 as catalyst and led to the (R)-N-
propionyloxazolidinone (R)-2 in 95% yield. Thus, in a four step
synthesis involving only small simple molecules (prop-2-ynylic
alcohol, CO2, NH3, AcCl and H2), the (R)-N-propionyl-
oxazolidinone (R)-2 was isolated with an enantiomeric excess
BH3
H
H
H
Ph2P
Ph2P
i
ii
O
O
O
N
N
N
H
H
Ph2P
H2
(i) LDA
O
O
O
O
O
O
O
O
O
N
N
N
(ii) Ph2PCl
[Ru]*
(R)-2
(R,R)-3
87%, 90% de
(R,R)-6
47%, 100% de
O
O
O
O
O
O
2
3
1
Scheme 3 Reagents and conditions: i, LDA, THF, 290 °C, then Ph2PCl,
290 °C to room temp.; ii, BH3·SMe2
Scheme 1
Chem. Commun., 1998
533

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H
(10 H, Ph); dC(75.5 MHz, CDCl3) 13.39 (q, J 131.2), 13.68 (q, J 128.2),
21.59 (q, J 127.5), 27.51 (q, J 127.5), 34.75 (dd, J 137.9, 25.5), 59.37 (d, J
141.6), 81.46 (s), 126.65–133.72 (m), 152.87 (s), 171.09 (s); Calc. for
BC21H27NO3P: C, 65.81; H, 7.10; N, 3.65; P, 8.08. Found: C, 65.81; H,
7.14; N, 3.65; P, 7.93%. [a]D + 58 (c 1.0, CHCl3).
H
Ph2P
Ph2P
i
O
+
O
OMe
HN
N
O
O
O
O
(R,R)-3
(R)-8
(R)-7
1 R. Noyori, Asymmetric Catalysis in Organic Synthesis, Wiley, New
York, 1993; I. Ojima, Catalytic Asymmetric Synthesis, VCH, New York,
1993.
Scheme 4 Reagents and conditions: i, MeOH, K2CO3, room temp.
2 I. Hayashi, M. Konishi, M. Fukushima, T. Mise, M. Kagotani, M. Tajika
and M. Kumada, J. Am. Chem. Soc., 1982, 104, 180; P. Wimmer and
M. Widhalm, Tetrahedron: Asymmetry , 1995, 6, 657; H. Kubota and
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Matt and A. Pfaltz, Angew. Chem., Int. Ed. Engl., 1993, 32, 566;
G. J. Dawson, C. G. Frost and J. M. J. Williams, Tetrahedron Lett.,
1993, 34, 3149.
4 A. Togni, U. Burckhardt, V. Gramlich, P. S. Pregosin and R. Salzmann,
J. Am. Chem. Soc., 1996, 118, 1031.
5 J. M. Brown, D. J. Hulmes and P. J. Guiry, Tetrahedron, 1994, 50,
4493.
the optically active phosphine methyl ester (R)-7 in 90% yield
after column chromatography under N2 (Scheme 4).
In conclusion, we report the selective preparation of an
optically pure phosphinoacyloxazolidinone. The synthesis in-
volves the preparation of an optically active acyloxazolidinone
via catalytic enantioselective hydrogenation and its use as chiral
inductor for stereoselective phosphinylation. This type of new
compound has potential as a new heterobidentate ligand in
asymmetric catalysis, and as a building block for access to a
variety of optically active phosphorus derivatives via cleavage
of the oxazolidinone ring.
6 Y. Uozumi and T. Hayashi, J. Am. Chem. Soc., 1991, 113, 9887;
J. F. Marcaux, S. Wagaw and S. L. Buchwald, J. Org. Chem., 1997, 62,
1568.
Notes and References
7 T. Minami, Y. Okada, T. Otaguro, S. Tawaraya, T. Furiuki and
T. Okauchi, Tetrahedron: Asymmetry, 1995, 6, 2469.
8 Y. Nagagawa, M. Kanai, Y. Nagaoka and K. Tomioka, Tetrahedron
Lett., 1996, 37, 7805.
† E-mail: pierre.dixneuf@univ-rennes1.fr
‡ Selected data for (R)-2: dH (300 MHz, CDCl3) 1.14 (3 H, t, J 7.3, MeCH2),
1.26 (3 H, d, J 6.6, MeCH), 1.39 and 1.41 (2 3 3 H, 2 s, Me2C), 2.88 and
2.90 (2 H, m, J 16.0, 7.35, MeCH2CO), 4.16 (1 H, q, J 6.6, CHMe); dC(75.5
MHz, CDCl3) 8.35 (q, J 128), 14.69 (q, J 128), 21.55 (q, J 127), 27.83 (q,
J 128), 29.33 (t, J 128), 58.88 (d, J 147), 81.41 (s), 152.79 (s), 174.34 (s);
Calc. for C9H15NO3: C, 58.36; H, 8.16; N, 7.56. Found: C, 58.07; H, 8.45;
N, 7.60%. [a]D 251 (c 0.9, CHCl3).
§ Selected data for (R,R)-6: mp 141 °C; dP(121.5 MHz, CDCl3) 26.76 (q, J
48.8); dH(300 MHz, CDCl3) 1.09 (3 H, d, J 6.6, NCHCH3), 1.17 (3 H, s,
CMe2), 1.35 (3 H, s, CMe2), 1.42 [3 H, dd, J 15.5, 6.9, MeCH(PPh2)], 4.03
(1 H, q, J 6.6, NCHCH3), 5.50 [1 H, dq, J 12.7, 6.9, CH(PPh2)], 7.39–7.90
9 D. Enders and T. Berg, Synlett, 1996, 796.
10 D. J. Ager, I. Prakash and D. R. Schaad, Chem. Rev., 1996, 96, 835.
11 S. G. Davies, M. E. C. Polywka and H. J. Sanganee, Int. Appl. WO
95/18112, 1995.
12 J.-M. Joumier, J. Fournier, C. Bruneau and P. H. Dixneuf, J. Chem. Soc.,
Perkin Trans. 1, 1991, 3271.
Received in Liverpool, UK, 14th November 1997; 7/08223A
534
Chem. Commun., 1998