(S)-3,3'-dimethyl-2,2'-biquinoline N,N'-dioxide as an efficient catalyst for enantioselective addition of allyltrichlorosilanes to aldehydes [10]

Full text of DOI:10.1021/ja981091r

J. Am. Chem. Soc. 1998, 120, 6419-6420
6419
(
S)-3,3′-Dimethyl-2,2′-biquinoline N,N′-Dioxide as an
lective allylation of aldehydes with allyltrichlorosilanes that
exploits (S)-3,3′-dimethyl-2,2′-biquinoline N,N′-dioxide ((S)-2) as
a catalyst, which affords homoallylic alcohols in high enantiose-
lectivities of up to 92% ee.
Efficient Catalyst for Enantioselective Addition of
Allyltrichlorosilanes to Aldehydes
†
Makoto Nakajima,* Makoto Saito, Motoo Shiro, and
Shun-ichi Hashimoto
At the outset, we examined addition of allyltrichlorosilane to
benzaldehyde using 10 mol % of isoquinoline N-oxide as a
catalyst. As expected, the reaction in dichloromethane proceeded
smoothly at 23 °C for 12 h to afford the corresponding
homoallylic alcohol in 76% yield. Encouraged by this finding,
we undertook asymmetric allylation, employing 10 mol % of (S)-
Graduate School of Pharmaceutical Sciences
Hokkaido UniVersity, Sapporo 060-0812, Japan
X-ray Research Laboratory, Rigaku Corporation
Akishima 196-0003, Japan
1
,1′-biisoquinoline N,N′-dioxide ((S)-1),12 which was patterned
ReceiVed April 1, 1998
after (S)-1,1′-binaphthalene-2,2′-diol. However, the optical yield
obtained here (23 °C, 2 h) was found to be less satisfactory (82%
yield, 52% ee). To improve the enantioselectivity, we then
The rational design and synthesis of novel chiral ligands
directed toward catalytic, asymmetric reactions is currently the
3
a
focus of attention in synthetic organic chemistry.1 Given that
adopted (S)-3,3′-dimethyl-2,2′-biquinoline N,N′-dioxide ((S)-2)
amine N-oxides possess a notable electron-pair donor property
2,3
to form complexes with a variety of metals, the development
of chiral amine N-oxides as chiral ligands or catalysts should be
a significant addition to the field of asymmetric synthesis;
however, there have been reported only a few attempts to use
chiral amine N-oxides for this purpose.4 In this context, of
5
particular interest are the recent findings of Kobayashi and
6
Denmark that DMF or HMPA coordinates to the silicon atom
of allyltrichlorosilanes to form hypervalent silicates,7 which in
turn react with aldehydes via cyclic chairlike transition states to
afford the corresponding homoallylic alcohols in a regio- and
diastereospecific manner. As a logical extension of this reaction,
Denmark has reported the first example of the catalytic, asym-
,8
as a chiral catalyst, wherein the N-oxide moieties were embedded
within a chiral pocket created by the walls of the biaryl unit.
metric version by the use of chiral phosphoramide derivatives as
1
3
Lewis bases, albeit with modest levels of enantioselectivity.6,9,10
Indeed, we were gratified to find that the allylation reaction (23
°C, 2 h) under the influence of (S)-2 (10 mol %) gave the (R)-
enriched homoallylic alcohol in 90% yield and 71% ee. After
considerable experimentation based on (S)-2,14 we were very
surprised to find that the allylation was notably accelerated by
the addition of 5 equiv of diisopropylethylamine (23 °C, 10 min)
and virtually the same enantioselectivity as above was obtained
Since amine N-oxides are known to exhibit a significant nucleo-
philicity toward the silicon atom,11 we were intrigued by the
feasibility of this catalytic, asymmetric process based on chiral
amine N-oxide. Herein we describe a new catalytic, enantiose-
*
Address correspondence to this author at Hokkaido University.
Rigaku Corporation.
†
(
1) (a) Ojima, I., Ed. Catalytic Asymmetric Synthesis, VCH: New York,
(90% yield, 71% ee). The beneficial effect of diisopropylethyl-
1
993. (b) Noyori, R. Asymmetric Catalysis in Organic Synthesis; Wiley: New
York, 1994.
amine on the reaction rate made it possible to conduct the reaction
(
2) For a review on amine N-oxide complexes, see: Karayannis, N. M.;
at -78 °C, thereby enhancing the enantioselectivity up to 88%
Pytlewski, L. L.; Mikulski, C. M. Coord. Chem. ReV. 1973, 11, 93-159.
15-17
ee.
It is noteworthy that this remarkable activation is obtained
(3) Studies on bipyridine N,N′-dioxide derivatives by our group: (a)
Nakajima, M.; Sasaki, Y.; Shiro, M.; Hashimoto, S. Tetrahedron: Asymmetry
997, 8, 341-344. (b) Nakajima, M.; Sasaki, Y.; Iwamoto, H.; Hashimoto,
S. Tetrahedron Lett. 1998, 39, 87-88.
specifically with diisopropylethylamine, whereas other amines
1
(12) Homochiral 1 has been prepared via optical resolution with chiral
stationary phase column (Fujii, M.; Honda, A. J. Heterocycl. Chem. 1992,
29, 931-933). We successfully resolved the racemic dioxide via hydrogen-
bonding complex with (R)-binaphthol (see: ref 3a and Toda, F.; Mori, K.;
Stein, Z.; Goldberg, I. Tetrahedron Lett. 1989, 30, 1841-1844). Absolute
configuration was determined by X-ray crystallography of the hydrogen-
bonding complex. See the Supporting Information for the crystallographic
data.
(13) On the basis of the same concept, Wulff has prepared homochiral
3,3′-diphenyl-2,2′-binaphthalene-1,1′-diol, which exhibited better enantiose-
lectivity than 1,1′-binaphthalene-2,2′-diol in asymmetric Diels-Alder reaction.
See: Bao, J.; Wulff, W. D.; Rheingold, A. L. J. Am. Chem. Soc. 1993, 115,
3814-3815.
(14) Dichloromethane has been proven to be the solvent of choice at room
temperature. Solvent (% yield, ee): propionitrile (82, 61); tetrahydrofuran
(58, 34); ethyl acetate (45, 33); toluene (12, 27).
(
4) (a) Diana, M. B.; Marchetti, M.; Melloni, G. Tetrahedron: Asymmetry
1
995, 6, 1175-1179. (b) O’Neil, I. A.; Turner, C. D.; Kalindjian, S. B. Synlett
1
997, 777-780.
(
5) (a) Kobayashi, S.; Nishio, K. Tetrahedron Lett. 1993, 34, 3453-3456.
(
b) Kobayashi, S.; Nishio, K. J. Org. Chem. 1994, 59, 6620-6628.
6) Denmark, S. E.; Coe, D. M.; Pratt, N. E.; Griedel, B. D. J. Org. Chem.
994, 59, 6161-6163.
7) For recent reviews on hypervalent silicates, see: (a) Sakurai, H. Synlett
(
1
(
1
1
989, 1-8. (b) Chuit, C.; Corriu, R. J. P.; Reye, C.; Young, J. C. Chem. ReV.
993, 93, 1371-1448.
(8) For Lewis base promoted reactions based on hypervalent silicates other
than allylation, see: (a) Denmark, S. E.; Barsanti, P. A.; Wong, K.-T.;
Stavenger, R. A. J. Org. Chem. 1998, 63, 2428-2429. (b) Denmark, S. E.;
Wong, K.-T.; Stavenger, R. A. J. Am. Chem. Soc. 1997, 119, 2333-2334. (c)
Denmark, S. E.; Winter, S. B. D.; Su, X.; Wong, K.-T. J. Am. Chem. Soc.
1
1
4
5
996, 118, 7404-7405. (d) Kobayashi, S.; Nishio, K. J. Am. Chem. Soc. 1995,
17, 6392-6393. (e) Kobayashi, S.; Yasuda, M.; Hachiya, I. Chem. Lett. 1996,
07-408. (f) Kobayashi, S.; Tsuchiya, Y.; Mukaiyama, T. Chem. Lett. 1991,
37-540.
(15) General procedure of enantioselective allylation is as follows. To a
solution of (S)-2 (0.16 mmol), diisopropylethylamine (8.0 mmol), and
benzaldehyde (1.6 mmol) in dichloromethane (1.5 mL) was added allyltrichlo-
rosilane (1.9 mmol) at -78 °C. The mixture was stirred at the same temperature
for 6 h. Aqueous workup followed by silica gel column chromatography
afforded (R)-enriched R-(2-propenyl)benzenemethanol, the enantiomeric excess
of which was determined by HPLC. Amine N-oxide (S)-2 was recovered from
the column quantitatively without any loss of optical purity.
(16) The allylation promoted by dimethylformamide or triphenylphosphine
oxide has recently been reported to be accelerated by the addition of
tetraalkylammonium halide. See: Short, J. D.; Attenoux, S.; Berrisford, D. J.
Tetrahedron Lett. 1997, 38, 2351-2354.
(17) Allylation employing stoichiometric amount of (S)-2 without diiso-
propylethylamine at -78 °C for 24 h afforded the homoallylic alcohol of
88% ee in 90% yield.
(
9) Iseki and Kobayashi have recently improved the enantioselectivity by
employing a proline-based phosphoramide derivative as a chiral Lewis base.
See: (a) Iseki, K.; Kuroki, Y.; Takahashi, M.; Kobayashi, Y. Tetrahedron
Lett. 1996, 37, 5149-5150. (b) Iseki, K.; Kuroki, Y.; Takahashi, M.;
Kishimoto, S.; Kobayashi, Y. Tetrahedron 1997, 53, 3513-3526.
(10) For a review on chiral Lewis acid catalyzed allylation of aldehydes,
see: Cozzi, P. G.; Tagliavini, E.; Umani-Ronchi, A. Gazz. Chim. Ital. 1997,
27, 247-254.
1
(11) Trimethylamine N-oxide is known to cleave carbon-silicon bond via
hypervalent silicate intermediate. See: Sato, K.; Kira, M.; Sakurai, H.
Tetrahedron Lett. 1989, 30, 4375-4378.
S0002-7863(98)01091-9 CCC: $15.00 © 1998 American Chemical Society
Published on Web 06/14/1998

6420 J. Am. Chem. Soc., Vol. 120, No. 25, 1998
Communications to the Editor
Table 1. Enantioselective Allylation of Aldehydes with
Allyltrichlorosilane Catalyzed by (S)-2
Table 2. Enantioselective Allylation of Benzaldehyde with
Allyltrichlorosilanes Catalyzed by (S)-2
yield, ee,
yield, ee,
a
b
(config)b
[R] c
entry
R
%
%
D
R1
R2
R3
a
b
(config)b
c
entry
%
%
[R]
D
1
6
9
9a
1
2
3
4
5
6
7
8
9
Ph
4-MeOC
4-CF
2-MeC
1-naphthyl
(E)-C
(E)-PhCHdCH
85
91
71
70
68
88
92
71
90
88
81
80
7
(R)
(R)
(R)
+38.5 (C
+45.1 (C
+24.6 (C
6
6
6
H
H
H
6
6
6
)
)
)
d
68f
64
52
70
19d
19d
19e
1
2
H
CH
H
CH
H
3
H
H
H
CH
86 (1R,2R) +94.6 (CHCl
84 (1R,2S) +22.6 (CHCl
78 (R)
49 (R)
3
3
3
)
)
)
6
H
4
e
g
CH
CH
H
3
d
3
C
6
6
H
4
3
4
3
3
+46.4 (CHCl
+24.0 (C H )
6 6
d
6
H
4
(R)
+39.2 (EtOH)
19a
1
9b
3
(R)
(R)
(R)
(S)
(S)
+84.7 (C
6 6
H )
e
f
19c
a
Isolated yield. b Determined by HPLC analysis employing a Daicel
Chiralcel OD, OJ, or Chiralpak AD. Configuration assignment by
7
H
15CHdCH 74
+3.2 (CHCl )
3
19a
87
30
27
-11.3 (Et
2
O)
1
9a
c
Ph(CH
c-Hex
2
)
2
-2.5 (CHCl
3
)
comparison to literature values of optical rotations. Observed optical
g
19c
rotations and literatures. E:Z ) 97:3. e E:Z ) 1:99. syn:anti ) 3:97.
d
f
28
-3.5 (EtOH)
g
syn:anti ) 99:1.
a
Isolated yield. b Determined by HPLC analysis employing a Daicel
allyltrichlorosilane. These results suggest that the allylations of
aromatic and unsaturated aldehydes mediated by (S)-2 proceed
via cyclic chairlike transition structures 3, involving hypervalent
silicates where one of a pair of N-oxide moieties occupies an
axial position. In this respect, it is of interest to note that the
Chiralcel OD, OJ, or Chiralpak AD. Configuration assignment by
c
comparison to literature values of optical rotations. Observed rotations
d
e
and literatures. Assignment by analogy. The reaction was carried
f
out with 20 mol % of (S)-2. Determined by HPLC analysis of the
corresponding 4-nitrobenzoate. Determined by HPLC analysis of the
g
corresponding 3,5-dinitrobenzoate.
such as triethylamine, pyridine, and diaza[2.2.2]bicyclooctane
showed the relatively modest effects. While the role of diiso-
propylethylamine is presently unclear, it may be reasonable to
assume that the amine promotes a dissociation of (S)-2 from
silicon atom in the product by ligand exchange to regenerate (S)-2
because the addition of the amine does not influence the sense
and extent of the enantioselection.
The results obtained for the reaction of a variety of aldehydes
with allyltrichlorosilane are summarized in Table 1. Allylation
of aromatic aldehydes gave results similar to those with benzal-
dehyde, except in the case of 4-(trifluoromethyl)benzaldehyde
bearing an electron-withdrawing group (entry 3). It is worthy of
note that the enantioselectivity (92% ee) observed with anisal-
dehyde is the highest reported to date for enantioselective
allylations of aldehydes with allyltrichlorosilane catalyzed by a
chiral Lewis base (entry 2). While the present protocol could be
extended to R,â-unsaturated aldehydes (entries 6 and 7), aliphatic
aldehydes (entries 8 and 9) proved to be unsuitable substrates in
terms of both chemical yield and enantioselectivity.
allylation using sterically congested prenyltrichlorosilane still
maintained good enantioselectivity in accord with a general trend
(entry 3), whereas a dramatic drop in enantioselectivity was
observed with methallyltrichlorosilane (entry 4). On the basis
of the above hypothesis, the latter result may also be rationalized
by assessing the 1,3-diaxial-type steric repulsion between the
methyl group and the wall of the biaryl unit.
In summary, we have demonstrated the effectiveness of (S)-
3,3′-dimethyl-2,2′-biquinoline N,N′-dioxide ((S)-2) as a catalyst
To establish the mechanistic profile of the amine N-oxide-
for enantioselective addition of allyltrichlorosilanes to aldehydes,
wherein the use of diisopropylethylamine as an additive has
proven to be crucial for the acceleration of the catalytic cycle.
Studies on the mechanism as well as the design of chiral amine
N-oxides to further enhance enantioselectivity are currently in
progress.
promoted process, we then examined allylations of benzaldehyde
with (E)- and (Z)-crotyltrichlorosilanes.18 As shown in Table 2,
γ-allylated anti-homoallylic alcohol was obtained from (E)-
crotyltrichlorosilane (entry 1) while corresponding syn-alcohol
was produced from (Z)-crotyltrichlorosilane (entry 2), both in
virtually complete regio- and diastereoselectivities. In each case,
the consistent sense and magnitude of the asymmetric induction
at the hydroxy center was observed as in the case of the parent
Acknowledgment. This research was supported in part by the Special
Coordination Funds of the Science and Technology Agency of the
Japanese Government.
(
18) For preparation of allyltrichlorosilanes, see: (a) Furuya, N.; Sukawa,
T. J. Organomet. Chem. 1975, 96, C1-C3. (b) Kira, M.; Hino, T.; Sakurai,
Supporting Information Available: Preparation of (S)-1, X-ray
crystallographic data of (S)-1‚(R)-binaphthol complex, procedure of
H. Tetrahedron Lett. 1989, 30, 1099-1102.
(
19) (a) Minowa, N.; Mukaiyama, T. Bull. Chem. Soc. Jpn. 1987, 60, 3697-
1
13
enantioselective allylation, and H, C NMR, HPLC data of all
homoallylic alcohols are provided (15 pages, print/PDF). See any current
masthead page for ordering information and Web access instructions.
3
2
704. (b) Sugimoto, K.; Aoyagi, S.; Kibayashi, C. J. Org. Chem. 1997, 62,
322-2323. (c) Roush, W. R.; Hoong, L. K.; Palmer, M. A. J.; Park, J. C. J.
Org. Chem. 1990, 55, 4109-4117. (d) Roush, W. R.; Ando, K.; Powers, D.
B.; Palkowiz, A. D.; Halterman, R. L. J. Am. Chem. Soc. 1990, 112, 6339-
6
348. (e) Manabe, S. Chem. Commun. 1997, 737-738.
JA981091R