Novel diphosphite derived from D-gluco-furanose provides high regio- and enantioselectivity in Rh-catalysed hydroformylation of vinyl arenes

Article abstract of DOI:10.1039/b004799f

Both high enantioselectivity (91%) and high regioselectivity (98.8%) are achieved under mild reaction conditions in the Rh-catalysed hydroformylation of vinyl arenes with a new chiral diphosphite ligand derived from the readily available D-(+)-glucose.

Full text of DOI:10.1039/b004799f

Novel diphosphite derived from
D-gluco-furanose provides high regio- and
enantioselectivity in Rh-catalysed hydroformylation of vinyl arenes
a
a
a
b
a
Montserrat Diéguez,* Oscar Pàmies, Aurora Ruiz, Sergio Castillón and Carmen Claver
a
Departament de Química Física i Inorgànica, Universitat Rovira i Virgili, Pl. Imperial Tarraco 1, 43005
Tarragona, Spain. E-mail: dieguez@quimica.urv.es
Departament de Química Analítica i Orgànica, Universitat Rovira i Virgili, Pl. Imperial Tarraco 1, 43005
Tarragona, Spain
b
Received (in Cambridge, UK) 15th June 2000, Accepted 14th July 2000
Published on the Web 4th August 2000
Both high enantioselectivity (91%) and high regioselectivity
(
98.8%) are achieved under mild reaction conditions in the
Rh-catalysed hydroformylation of vinyl arenes with a new
chiral diphosphite ligand derived from the readily available
D
-(+)-glucose.
Asymmetric hydroformylation has attracted much attention as a
potential tool for preparing enantiomerically pure aldehydes.
These are important as precursors for synthesising biologically
active compounds, biodegradable polymers and liquid crystals.1
In the last ten years, several studies have reported a remarkable
improvement in the rhodium-catalysed asymmetric hydro-
2
formylation based on the use of diphosphite or phosphine–
3
phosphite (Binaphos) ligands. At the moment, Binaphos is the
only ligand with a wide scope in asymmetric hydroformylation,
although its difficult preparation limits its application. Fur-
thermore, its regioselectivy in 2-phenylpropanal is not com-
pletely satisfactory even under carefully optimised conditions.3
More recently, perfluoroalkyl substituents at the aryl group of
the Binaphos increased the regioselectivity, in the best case up
to 96%, but high pressures and an excess of ligand were still
Scheme 1
4
needed for good enantioselectivities. In this context, much
research still needs to be done to find ligands that are readily
available and provide both good regio- and enantioselectivities
in asymmetric hydroformylation.
Ligand 4 was used in the rhodium-catalysed asymmetric
hydroformylation of styrene and other vinylarenes. Results
are given in Table 1. In no cases were hydrogenated or
polymerised products observed.
14
In the last few decades carbohydrates have been widely used
5
in asymmetric synthesis. Nevertheless their full potential in
Varying the ligand-to-rhodium ratio shows that it is not
necessary to have excess ligand to obtain good regio- and
enantioselectivities (entries 1–2). This contrasts with Rh–
Binaphos systems, for which a large excess of ligand is
6
providing chiral ligands has scarcely been exploited despite the
accessibility and low cost of the carbohydrate synthons. In
previous work on diphosphite ligands with a furanose backbone
moderate results (up to 60% ee) in asymmetric hydro-
3,4
needed. Moreover, activities were best at low PCO–PH2 ratios
7
formylation of styrene have been reported. Since these ligands
had a phosphorus moiety bonded to a nonstereogenic center (C-
5
), we tested whether further modifying the ligand would
improve enantioselectivities. With this purpose and following
from our interest in using carbohydrates as a chiral source for
preparing ligands,7 we designed a new diphosphite ligand 4
b,8
which was easily prepared from
the two phosphite moieties bonded to two stereogenic centers
C-3 and C-5) and has proven to be highly enantioselective and
D-(+)-glucose. This ligand has
(
regioselective in the asymmetric hydroformylation of vinylar-
enes (Scheme 1).
Diphosphite 49 was synthesised in 3 steps from 1,2-O-
isopropylidene-3-O-acetyl-a-
D
-glucofuranose 5 as shown in
Scheme 2. Diol 5 is easily prepared from
D
-(+)-glucose on a
large scale by previously described highly effective methods.10
Tosylation of 5 produced a good yield of the expected 5-tosyl
derivative (88%).11 Treatment with NaOMe at rt followed by
reduction with lithium aluminium hydride produced crystalline
6
-deoxy-1,2-O-isopropylidene-a- -glucofuranose 7 in 92%
D
12
yield.
Reacting diol 7 with two equiv. of 3,3A-di-tert-butyl-5,5A-di-
methoxy-1,1A-biphenyl-2,2A-diyl phosphorochloridite13 in situ
formed in the presence of pyridine produced the desired
diphosphite 4 in good overall yield.
Scheme 2 Synthesis of ligand 4: (i) TsCl, pyridine, CH
2 2
Cl , 16h, 220 to
2
5 °C, 88%; (ii) NaOMe, CH Cl , 1 h, 25°C, quantitative; (iii) LiAlH ,
2
2
4
THF, 60 °C, 92%; (iv) phosphorochloridite, pyridine, toluene, 100 °C,
71%.
DOI: 10.1039/b004799f
Chem. Commun., 2000, 1607–1608
This journal is © The Royal Society of Chemistry 2000
1607

Table 1 Asymmetric hydroformylation catalysed by [Rh(acac)(CO)
]/4a
2
Notes and references
%
Conv
1 (a) M. Beller, B. Cornils, C. D. Frohning and V. W. Kohlpainter, J. Mol.
Catal., 1995, 104, 17; (b) F. Agboussou, J. F. Carpentier, A. Mortreux,
Chem. Rev., 1995, 95, 2485.
Entry Substrate PCO–PH2 T/°C TOFb (time/h) %Regiod %Eee
c
1
2
3
4
5
6
a
1a
1a
1a
1a
1b
1c
1
1
0.5
0.5
0.5
0.5
40
40
40
20
20
20
98
97
174
18
17
16
98 (10) 97.8
96 (10) 97.7
78 (S)
78 (S)
78 (S)
90 (S)
89 (+)
91 (2)
2 (a) J. E. Babin and G. T. Whiteker, WO 93/03839, US 911, 518, 1992;
(b) G. J. H. Buisman, L. A. van deer Veen, A. Klootwijk, W. G. J. de
Lange, P. C. J. Kamer, P. W. N. M. van Leeuwen and D. Vogt,
Organometallics, 1997, 16, 2929.
3 K. Nozaki, N. Sakai, T. Nanno, T. Higashijima, S. Mano, T. Horiuchi
and H. Takaya, J. Am. Chem. Soc., 1997, 119, 4413.
f
100 (6)
97.9
83 (48) 98.6
80 (48) 98.8
81 (48) 98.6
4
5
G. Franciò and W. Leitner, Chem. Commun., 1999, 1663.
(a) S. Hanessian in Total Synthesis of Natural Products: The “Chiron”
Approach, Pergamon Press, vol. 3, London 1983; (b) J. S. Penne in
Chiral Auxiliaries and Ligands in Asymmetric Synthesis, John Wiley &
Sons, New York, 1995.
2
Reaction conditions: P = 10 bar, styrene (13 mmol), [Rh(acac)(CO) ]
b
21
(
0.013 mmol), toluene (15 mL), PP/Rh = 1.1. TOF in mol styrene 3 Rh
21
c
3
h
determined after 1 h reaction time by GC. % Conversion of styrene
measured by GC. % Regioselectivity defined as 2/(2 + 3). e % Ee
d
f
measured by GC. PP/Rh = 2.
6
(a) H. U. Blaser, Chem. Rev., 1992, 92, 935; (b) H. Brunner and W.
Zettlmeier in Handbook of Enantioselective Catalysis, VCH, Wein-
heim, 1993; (c) T. V. RajanBabu and T. A. Ayers, Tetrahedron Lett.,
(
entry 3). This is in line with detailed kinetic studies on
1
994, 35, 4295; (d) M. T. Reetz and T. Neugebauer, Angew. Chem., Int.
rhodium-catalysed hydroformylation with bulky phosphites
Ed., 1999, 38, 179; (e) T. V. RajanBabu, B. Radetich, K. K. You, T. A.
Ayers, A. L. Casalnuovo and J. C. Calebrese, J. Org. Chem., 1999, 64,
3429 and references cited therein; (f) K. Yonehara, T. Hashizume, K.
Mori, K. Ohe and S. Uemura, Chem. Commun., 1999, 415
7 (a) G. J. H. Buisman, M. E. Martin, E. J. Vos, A. Klootwijk, P. C. J.
Kamer and P. W. N. M. van Leeuwen, Tetrahedron: Asymmetry, 1995,
reported by van Leeuwen et al., who showed that the rate-
determining step is the oxidative addition of H to the acyl–
2
rhodium complex.15 Comparing entries 1 and 3 also shows that
regio- and enantioselectivities are not affected by varying the
partial pressure of CO. A remarkable increase in enantio-
selectivities (up to 91%, entries 4–6) combined with excellent
regioselectivities (up to 98.8%) were found by lowering the
reaction temperature. There were no changes in the enantio-
selectivities over time, which indicates that no decomposition of
the catalyst took place.
6
, 719; (b) O. Pàmies, G. Net, A. Ruiz and C. Claver, Tetrahedron:
Asymmetry, 2000, 11, 1097.
8
(a) O. Pàmies, G. Net, A. Ruiz, C. Bó, J. M. Poblet and C. Claver,
J. Organomet. Chem., 1999, 586, 125; (b) O. Pàmies, M. Diéguez, G.
Net, A. Ruiz and C. Claver, J. Chem. Soc., Dalton Trans., 1999, 3439;
(c) O. Pàmies, G. Net, A. Ruiz and C. Claver, Tetrahedron: Asymmetry,
Results were similar when 4 was used in the asymmetric
hydroformylation of the substituted vinylarenes 1b and 1c. The
presence of different substituents in the para position does not
seem to affect the conversion or the regio- and enantioselectiv-
ities of the hydroformylation.
1999, 10, 2007; (d) O. Pàmies, M. Diéguez, G. Net, A. Ruiz and C.
Claver, Organometallics, 2000, 19, 1488; (e) O. Pàmies, G. Net, A. Ruiz
and C. Claver, Eur. J. Inorg. Chem., in the press.
9
P 2 2
Selected data for 4: d (CD Cl , 233 K) 144.6 (d, 1P, JP2P = 30.9 Hz),
1
45.1 (d, 1P, JP2P = 30.9 Hz).
1
1
0 O. T. Schmidt in Methods in Carbohydrate Chemistry, eds. R. L.
Whistler and M. L. Wolfrom, Academic Press, New York, 1963, Vol.
II.
1 Compound 6 was preprared by a minor modification of the procedure
described in M. Nakjima and S. Takahashi, Agric. Biol. Chem., 1967,
31, 1079.
In conclusion, a novel chiral diphosphite 4, derived from
readily available -(+)-glucose, is a highly efficient ligand for
D
the asymmetric rhodium-catalysed hydroformylation of vinyl
arenes under mild reaction conditions and without an excess of
ligand. The combination of excellent regio- and enantioselectiv-
ities (up to 98.8 and 91% respectively) in simple unoptimised
reactions and the low cost of the ligand make this catalyst
system attractive for further investigation of its potential use for
the industrial preparation of biologically active compounds in
asymmetric hydroformylation. Studies of the scope and mecha-
nistic aspects of the catalytic process are currently in pro-
gress.
12 J. Hiebl and E. Zbiral, Monatsh. Chem., 1990, 121, 691.
13 3,3A-di-tert-butyl-5,5A-dimethoxy-1,1A-biphenyl-2,2A-diyl phosphoro-
chloridite is easily prepared in one step from the corresponding biphenol
as described in (a) G. J. H. Buisman, P. C. J. Kamer and P. W. N. M. van
Leeuwen, Tetrahedron: Asymmetry, 1993, 4, 1625. The corresponding
biphenol is easily prepared on large scale in the same way as the related
4
,4A,6,6A-tetra-tert-butyl-2,2A-biphenol described in (b) T. Jongsma, M.
Fossen and P. W. N. M. van Leeuwen, J. Mol. Catal., 1993, 83, 17.
4 The standard hydroformylation procedure is described in ref. 8d.
15 A. van Rooy, E. N. Orij, P. C. J. Kamer and P. W. N. M. van Leeuwen,
We thank the Spanish Ministerio de Educación y Cultura and
the Generalitat de Catalunya (CIRIT) for their financial support
1
(PB97-0407-CO5-01).
Organometallics, 1995, 14, 34.
1608
Chem. Commun., 2000, 1607–1608