Rhodium-catalyzed asymmetric [4 + 1] cycloaddition

Full text of DOI:10.1021/ja964259m

2950
J. Am. Chem. Soc. 1997, 119, 2950-2951
Scheme 1
Rhodium-Catalyzed Asymmetric [4 + 1]
Cycloaddition
Masahiro Murakami,* Kenichiro Itami, and Yoshihiko Ito*
Department of Synthetic Chemistry
and Biological Chemistry
Kyoto UniVersity, Yoshida, Kyoto 606-01, Japan
ReceiVed December 10, 1996
Carbon monoxide is an important C1 source, and transition
metal-catalyzed carbonylation reactions have offered useful
methods for the synthesis of various carbonyl compounds
ranging from industrial processes to small-scale laboratory
preparations.1 The outstanding synthetic utility has stimulated
many attempts to develop a catalytic asymmetric carbonylation
reaction, yet only limited success has been achieved.2 This is
probably because carbon monoxide is among the most common
σ-donor/π-acceptor ligands and, hence, is capable of displacing
chiral auxiliaries. In the last few years, major breakthroughs
have been achieved in this area.3 We have recently reported a
new rhodium(I)-catalyzed carbonylation reaction (i.e., [4 + 1]
cycloaddition of vinylallenes with carbon monoxide).4 An
important feature of the reaction is that η4-coordination of a
vinylallene in an s-cis conformation to rhodium (A) occurs prior
to the incorporation of carbon monoxide (Scheme 1). Face-
selection of the conjugated diene system can potentially be
provided by a rhodium catalyst modified by a chiral ligand,
leading to an enantioselective carbonylation reaction. This paper
describes the first example of catalytic asymmetric [4 + 1]
cycloaddition of vinylallenes with carbon monoxide which
furnishes chiral 5-substituted 2-alkylidene-3-cyclopentenones
with moderate to high enantioselectivity.
Table 1. Effect of CO Pressure
entry
CO pressure (atm)
2a:3
% ee of 2a
1
2
3
1
5
15
53:47
97:3
100:0
42.3
64.5
61.6
Scheme 2
The catalyst precursors for the asymmetric carbonylation of
vinylallenes were prepared by treatment of a cationic complex
[Rh(cod)2]PF6 (5 mol %) with chiral diphosphine ligands (6
mol %), most of which are commercially available. The
resultant complexes were very effective catalysts for the
carbonylative [4 + 1] cycloaddition of vinylallenes at 60-80
°C, affording 2-alkylidene-3-cyclopentenone in good chemical
yield. Preliminary screening of a series of chiral diphosphine
ligands validated the occurrence of face-selection by the rhodium
complexes, and (R,R)-Me-DuPHOS [1,2-bis(2,5-dimethylphos-
phorano)benzene]5 was found to be the chiral ligand of choice.
Next, the solvent effect was examined using (R,R)-Me-DuPHOS
in the reaction of vinylallene (1a) under 1 atm of carbon
monoxide. 1,2-Dimethoxyethane (DME) gave the best enan-
tioselectivity (42.3% ee, Table 1, entry 1) among tested solvents
(MeOH, toluene, THF, CH2Cl2, etc.). The reaction suffered,
however, from the formation of a conjugated triene (3),6 which
was probably formed through â-hydride elimination of the
intermediate metallacyclopent-3-ene followed by reductive
elimination (Scheme 2). It was found that increase of CO
pressure suppressed the formation of 3. This was understood
in terms of acceleration of migratory insertion of carbon
monoxide with metallacyclopent-3-ene (B) in preference to
â-hydride elimination. Moreover, the enantioselectivity was also
affected by the CO pressure, and the reaction under 5 atm of
CO afforded 2a in 64.5% ee (entry 2). Although the origin of
the enantioselectivity has not been fully elucidated, the stereo-
determining step at 5 atm of CO pressure appears to carry the
largest bias of the enantioface differentiation.
The standard set of the reaction conditions (5 atm of CO, in
DME, 60 °C, 6-14 h) was next applied to carbonylation of a
variety of vinylallenes, producing cyclopentenones 2 with
moderate to good enantioselectivity in high isolated yield (Table
2). It is a formidable task to gain stereocontrol over a substrate
lacking directive heteroatom functionalities using transition
metal complexes.7 In this regard, it is noteworthy that a useful
level of asymmetric induction was attained with these substrates,
as listed in Table 2.
(1) Colquhoun, H. M.; Thompson, D. J.; Twigg, M. V. Carbonylation:
Direct Synthesis of Carbonyl Compounds; Plenum: New York, 1991.
(2) (a) Consiglio, G. In Catalytic Asymmetric Synthesis; Ojima, I., Ed.;
VCH: New York, 1993; pp 273-302. (b) Agbossou, F.; Carpentier, J.-F.;
Mortreux, A. Chem. ReV. 1995, 95, 2485-2506. (c) Gladiali, S.; Bayn, J.
C.; Claver, C. Tetrahedron: Asymmetry 1995, 6, 1453-1474.
(3) Hydroformylation: (a) Sakai, N.; Mano, S.; Nozaki, K.; Takaya, H.
J. Am. Chem. Soc. 1993, 115, 7033-7034. (b) Sperrle, M.; Consiglio, G.
J. Am. Chem. Soc. 1995, 117, 12130-12136. Alternating carbonylative
copolymerization: (c) Brookhardt, M.; Wagner, M. I.; Balavoine, G. G.
A.; Haddou, H. A. J. Am. Chem. Soc. 1994, 116, 3641-3642. (d) Bronco,
S.; Consiglio, G.; Hutter, R.; Batistini, A.; Suter, U. W. Macromolecules
1994, 27, 4436-4440. (e) Jiang, Z.; Sen, A. J. Am. Chem. Soc. 1995, 117,
4455-4467. (f) Nozaki, K.; Sato, N.; Takaya, H. J. Am. Chem. Soc. 1995,
117, 9911-9912.
(4) (a) Murakami, M.; Itami, K.; Ito, Y. Angew. Chem., Int. Ed. Engl.
1995, 34, 2691-2693. (b) Murakami, M.; Itami, K.; Ito, Y. J. Am. Chem.
Soc. 1996, 118, 11672-11673.
(5) For asymmetric reactions based on DuPHOS, see: Burk, M. J.; Wang,
Y. M.; Lee, J. R. J. Am. Chem. Soc. 1996, 118, 5142-5143 and references
cited therein.
Finally, carbonylation of vinylallenes (4) bearing an ester
group was examined. The cycloaddition proceeded at lower
temperatures giving remarkably improved selectivities, and
(6) No [4 + 1] cycloadduct potentially arising from 3 was detected, being
suggestive of the superior reactivity of a vinylallene skeleton.
(7) For leading examples, see: (a) Jacobsen, E. N.; Marko´, I.; Mungall,
W. S.; Schro¨der, G.; Sharpless, K. B. J. Am. Chem. Soc. 1988, 110, 1968-
1970. (b) Hayashi, T.; Matsumoto, Y.; Ito, Y. J. Am. Chem. Soc. 1989,
111, 3426-3428. (c) Zhang, W.; Loeback, J. L.; Wilson, S. R.; Jacobsen,
E. N. J. Am. Chem. Soc. 1990, 112, 2801-2803. (d) Uozumi, Y.; Hayashi,
T. J. Am. Chem. Soc. 1991, 113, 9887-9888. (e) Ohta, T.; Ikegami, H.;
Miyake, T.; Takaya, H. J. Organomet. Chem. 1995, 502, 169-176. (f)
Kondakov, D. Y.; Negishi, E. J. Am. Chem. Soc. 1995, 117, 10771-10772.
S0002-7863(96)04259-X CCC: $14.00 © 1997 American Chemical Society

Communications to the Editor
J. Am. Chem. Soc., Vol. 119, No. 12, 1997 2951
Table 2. Asymmetric [4 + 1] Cycloaddition of Vinylallenes (1)
Figure 1.
was determined to be S by the 1H NMR study of the O-methyl
mandelate ester9 derived from 6.
We have found that a vinylallene having a substituent at the
vinylic terminus coordinates to rhodium(I) in a η4-fashion.4 On
the basis of η4-binding, the stereochemical outcome was
explained by assuming the following models for the formation
of a vinylallene-rhodium complex (Figure 1). Model I is
disfavored because of the two major repulsive steric interactions,
one between the methyl group on the phosphorano ring and
the R2 group and the other between another ligand methyl group
and the substrate methyl group at the allenic terminus. Model
II is free from these interactions, with the vinylallene fitting
better to the chiral environment. The coordination depicted in
Model II is consistent with the observed absolute stereochem-
istry of the product.
a Enantioselectivity was determined by chiral HPLC analysis.
Table 3. Asymmetric [4 + 1] Cycloaddition of Vinylallenes (4)
Asymmetric cycloaddition is a powerful tool to construct
complex chiral molecules.10 The asymmetric carbonylative [4
+ 1] cycloaddition documented herein adds a new promising
example which achieves enantioselectivities up to 95% ee. The
optimal selectivity is commensurate with those accomplished
in precedent highly effective systems like chiral Lewis acid-
promoted Diels-Alder type [4+2] cycloaddition.
6
R
yield from 4 (%)
% eea
6a
6b
6c
Et
93
96
94
92.0
91.5
95.0
Bui
CH2Ph
Acknowledgment. Support from Mitsubishi Petrochemical
Research Foundation is gratefully acknowledged.
a Enantioselectivity was determined by chiral HPLC analysis.
particularly, the reaction of the benzyl ester (4c) at 10 °C
provided 5 with the highest enantioselectivity of 95.0% ee (Table
3). Successive treatment of the cyclopentenones (5) with
NaBH4-CeCl38 caused exclusive 1,2-reduction of the carbonyl
group to produce cis-cyclopentenols (6) stereoselectively, prob-
ably via the hydride approach from the less-hindered side, in
high yield based on the starting vinylallenes (4). The absolute
configuration of the major enantiomer given by (R,R)-DuPHOS
Supporting Information Available: Experimental details and
characterization for 2, 3, 5, and 6 (3 pages). See any current masthead
page for ordering and Internet access instructions.
JA964259M
(9) Trost, B. M.; Belletire, J. L.; Godleski, S.; Baldwin, J. J.; Christy,
M. E.; Ponticello, G. S. J. Org. Chem. 1986, 51, 2370-2374. The absolute
configurations of 2a-d also proved to be S according to the analogous
1
derivatization and H NMR studies.
(10) (a) Lautens, M.; Klute, W.; Tam, W. Chem. ReV. 1996, 96, 49-92.
(b) Ojima, I.; Tzamarioudaki, M.; Li, Z.; Donovan, R. J. Chem. ReV. 1996,
96, 635-662.
(8) Gemal, A. L.; Luche, J.-L. J. Am. Chem. Soc. 1981, 103, 5454-
5459.