J . Org. Chem. 1999, 64, 9735-9738
9735
ESP HOS a n d SEMI-ESP HOS: A New
F a m ily of Mon o- a n d Bid en ta te
Dia za p h osp h olid in e Liga n d s for
Asym m etr ic Ca ta lysis
a
Reagents and conditions: (i) 10 mol% 1a -c, 5 mol% [PdCl-
CH2CHCH2)]2, NaOAc, BSA, CH2(CO2Me)2.
Simon Breeden and Martin Wills*
(
Department of Chemistry, University of Warwick,
Coventry, CV4 7AL, UK
examined the use of diazaphospholidine ligands 1 derived
from enantiomerically pure 1,2-diaminocyclohexane in
the control of the allylic substitution reaction of diphenyl-
Received J uly 29, 1999
3
-acetoxy-1-propene with benzylamine and dimethyl ma-
In tr od u ction
7
lonate (Scheme 1). Of the ligands which we studied, the
derivative containing an o-methoxy group on the aro-
matic ring bound to the phosphorus atom gave the
products with the highest enantioselectivity. Deletion of
the methoxy group in the ligand results in almost
complete loss of enantioselectivity and reversal of con-
figuration in the product while, unexpectedly, the re-
placement of methoxy with ethyl results in a product of
identical absolute configuration but somewhat reduced
ee (Table 1). These results suggest that the methoxy
group in 1a is performing a somewhat unquantified role
as a “hemilabile” ligand.8
A large number of phosphorus-donor ligands have been
developed for use in catalytic asymmetric reactions. The
1
most widely studied class reported to date are phos-
phines, notably BINAP2 and DuPHOS,3 both of which
have been widely adopted in commercially important
applications such as asymmetric hydrogenation.
In contrast, phosphorus ligands containing alternative
4
5
donor units, such as phosphites or diazaphospholidines,
have been less widely examined. In this paper we report
the synthesis and preliminary studies on catalytic ap-
plications of a family of readily available ligands based
on the diazaphospholidine structure, which consist of
both monodentate and bidentate derivatives.
-11
Resu lts a n d Discu ssion
In a series of ongoing studies directed at the evaluation
6
of P donor ligands containing P-N bonds, we recently
Such a “hemilabile” effect of a methoxy group has been
previously described by other researchers. An excellent
recent example has been reported by Rajanbabu, who
employed the methoxy-substituted phosphine ligand
MOP in a nickel-catalyzed hydrovinylation reaction to
*
Corresponding author. Tel. (+24) 7652 3260. Fax. (+24) 7652 4112.
e-mail m.wills@warwick.ac.uk.
1) (a) Asymmetric Catalysis in Organic Synthesis; Noyori, R.; J ohn
(
Wiley and Sons Ltd: New York, 1994. (b) Catalytic Asymmetric
Synthesis; Ojima, I., Ed.; VCH Press: Berlin, 1993. (c) Asymmetric
hydrogenation: Wills, M. In Supplement A3: The chemistry of double-
bonded functional groups; Patai, S., Ed.; J ohn Wiley and Sons Ltd.:
New York, 1994; Ch. 15, pp 781-842.
8
give a product of 63% ee. In a study analogous to ours,
replacement of the methoxy group of MOP with ethyl
resulted in a dramatic decrease in selectivity (to 13% ee),
while its replacement with benzyloxy resulted in a
modest improvement to the overall selectivity (to 80% ee).
In prior studies Hayashi had already demonstrated that
the methoxy group in the MOP ligand, while essential
for high selectivities, does not form a full bond to the
metal in palladium-catalyzed allylic substitution reac-
(
2) (a) Noyori, R. Chem. Soc. Rev. 1989, 18, 187. (b) Noyori, R.
Science 1990, 248, 1194. (c) Noyori, R.; Takaya, H. Acc. Chem. Res.
990, 23, 345. (c) Noyori, R. Tetrahedron 1994, 50, 4259. (d) Noyori,
1
R. Acta Chem. Scand. 1996, 50, 380. (e) Ohkuma, T.; Ooka, H.;
Hashiguchi, S.; Ikariya, T.; Noyori, R. J . Am. Chem. Soc. 1995, 117,
2
675. (f) Ohkuma, T.; Ooka, H.; Yamakawa, M.; Ikariya, T.; Noyori,
R. J . Org. Chem. 1996, 61, 4872. (g) Doucet, H.; Ohkuma, T.; Murata,
K.; Yokozawa, T.; Kozawa, M.; Katayama, E.; England, A. F.; Ikariya,
T.; Noyori, R. Angew. Chem., Int. Ed. 1998, 37, 1703.
(3) (a) Burk, M. In Handbook of Chiral Chemicals; Ager, D., Ed.;
9
tions. Other well-known ligands containing hemilabile
Marcel Dekker Inc.: New York, 1999; Ch. 18, pp 339-358. (b) Burk,
M. J .; Bedingfield, K. M.; Kiesman, W. F.; Allen, J . G. Tetrahedron
Lett. 1999, 40, 3093. (c) Burk, M. J .; Bienewald, F.; Harris, M.; Zanotti-
Gerosa, A. Angew. Chem., Int. Ed. 1998, 37, 1931.
methoxy groups include the well-established DiPAMP,
for which again replacement of methoxy by ethyl results
in a reduction, but not complete loss, of selectivity in
asymmetric hydrogenations.10 A number of other diphos-
(4) (a) BINAPHOS in hydroformylation: Horiuchi, T.; Ohta, T.;
Shirakawa, E.; Nozaki, K.; Takaya, H. J . Org. Chem. 1997, 62, 4285;
Nozaki, K.; Itoi, Y.; Shibahara, F.; Shirakawa, E.; Ohta, K.; Takaya,
H.; Hiyama, T. J . Am. Chem. Soc. 1998, 120, 4051. (b) BINAPHOS in
copolymerization: Nozaki, K.; Sato, N.; Tonomura, Y.; Yasutomi, M.;
Takaya, H.; Hiyama, T.; Matsubara, T.; Koga, N. J . Am. Chem. Soc.
(7) Tye, H.; Smyth, D.; Eldred, C.; Wills, M. Synlett 1997, 1053.
(8) Rajanbabu, T. V.; Nomura, N.; J in, J .; Park, H. J . Am. Chem.
Soc. 1998, 120, 459.
1
997, 119, 12779. (c) Asymmetric C-C bond forming reactions:
Feringa, B. L.; Pineschi, M.; Arnold, L. A.; Imbos, R. Angew. Chem.,
Int. Ed. Engl. 1997, 36, 2620.
(9) (a) Hayashi, T.; Iwamura, H.; Naito, M.; Matsumoto, Y.; Uozumi,
Y. J . Am. Chem. Soc. 1994, 116, 775. (b) Hayashi, T.; Iwamura, H.;
Uozumi, Y.; Matsumoto, Y.; Ozawa, F. Synthesis 1994, 526.
(10) Replacement of the methoxy groups in DiPAMP with ethyls
produces a ligand which is only marginally inferior, suggesting a
primarily steric role in this case: Imamoto, T. Tsuruta, H.; Wada, Y.;
Masuda, H.; Yamaguchi, K. Tetrahedron Lett. 1995, 36, 8271.
(11) Hemilabile effects in diphosphines have been examined in
detail: (a) Borns, S.; Kadyrov, R.; Heller, D.; Baumann, W.; Holz, J .;
Borner, A. Tetrahedron: Asymmetry 1999, 10, 1425. (b) Borns, S.;
Kadyrov, R.; Heller, D.; Baumann, W.; Spannenberg, A.; Kempe, R.;
Holz, J .; Borner, A. Eur. J . Inorg. Chem. 1998, 1291.
(
5) Diazaphospholidines related to ESPHOS: (a) Longeau, A.;
Durand, S.; Spiegel, A.; Knochel, P. Tetrahedron: Asymmetry 1997,
, 987. (b) Vasconcelos, I. C. F.; Anderson, G. K.; Rath, N. P.; Spilling,
8
C. D. Tetrahedron Lett. 1998, 9, 927. For diazaphospholidines related
to SEMI-ESPHOS, see ref 12.
(6) (a) Brenchley, G.; Merifield, E.; Wills, M.; Fedouloff, M. Tetra-
hedron Lett. 1994, 35, 2791. (b) Brenchley, G.; Fedouloff, M.; Mahon,
M. F.; Merifield, E.; Molloy, K. C.; Wills, M. Tetrahedron 1995, 51
1
0581. (c) Brenchley, G.; Fedouloff, M.; Merifield, E.; Wills, M.
Tetrahedron: Asymmetry 1996, 7, 2809.
1
0.1021/jo9912101 CCC: $18.00 © 1999 American Chemical Society
Published on Web 12/03/1999