Table 1 Allylic transfer reactions of 7 with achiral aldehydesab
°C for 1 h afforded 9 along with the corresponding silyl ether
less than 10%) which was readily desilylated with Bu NF in
THF (over all 71% yield).
In summary, this paper describes a new bifunctional reagent
for the catalytic asymmetric allylic transfer reaction in a very
general and efficient way which promises to be widely
applicable. We believe that the products can serve as synthetic
intermediates for the synthesis of chiral substances by selective
functional group transformations.
Generous financial support of this research by grants from the
Ministry of Education (BSRI 97-3420) and the Korea Science
and Engineering Foundation (KOSEF 97-0501-02-01-3) is
gratefully acknowledged.
(
4
HO
R
H
RCHO 2
Bu3Sn
SiMe3
(S)-BINOL-TiIV
3
Et2BSPri 4, –20 °C
SiMe3
7
8
Entry
R
Solvent
t/h
Yield (%)c
Ee (%)d
1
2
3
4
5
6
7
8
a
PhCH
PhCH
2
CH
CH
2
CH
PhCF
CH Cl
PhCF
CH Cl
PhCF
CH Cl
PhCF
2
Cl
3
2
2
2
2
18
18
18
18
24
24
24
24
62
78
60
83
39
54
50
62
92
97
90
97
84
91
83
88
2
2
C
C
6
H
H
13
2
6
13
3
Ph
Ph
2
Notes and references
3
Me
Me
3
3
SiC·C
SiC·C
2
i
†
Removal of Pr OH under reduced pressure after formation of catalyst
3
resulted in significantly diminished chemical yields. Also, according to the
results of control experiments under identical conditions except for the use
of aldehyde, we did not observe formation of any buta-2,3-dienylstannane
from 1.
‡ Compound 7 was prepared in quantity, purified by distillation, and is
stable to storage, whereas compound 1 could not be distilled and is
somewhat unstable to storage at 220 °C over more than a week.
All reactions were carried out at 220 °C in indicated solvent.
b
i
= 2:1 (10 mol%). c Yields refer to isolated and purified
BINOL:Ti(OPr )
4
d
products.
Ees were determined by preparation of (+)-MTPA ester
1
derivatives, analysis by 500 MHz H NMR spectroscopy, and comparison
with corresponding diastereomers which were prepared from (R)-BINOL-
IV
Ti
.
1
General discussions on chiral Lewis acids: R. Noyori, Asymmetric
Catalysis in Organic Synthesis, Wiley, New York, 1994, pp. 255–297;
K. Maruoka and H. Yamamoto, in Catalytic Asymmetric Synthesis, ed.
I. Ojima, VCH, New York, 1993, pp. 413–440; K. Mikami in Advances
in Catalytic Process, ed. M. P. Doyle, JAI Press, Greenwich, 1995, pp.
results are summarised in Table 1. It is noteworthy that the
formation of bis-allylated diol was not detected. Also, reduced
dosage of chiral catalyst 3 (5 mol%) resulted in diminished
chemical yield and longer reaction time (2, R = PhCH
20 °C, 36 h, 34%).
The absolute configuration of the predominating enantiomer
2 2
CH ,
1
–44.
2
2
C.-M. Yu, H.-S. Choi, W.-H. Jung, H.-J. Kim and J. Shin, Chem.
Commun., 1997, 761; C.-M. Yu, H.-S. Choi, W.-H. Jung and S.-S. Lee,
Tetrahedron Lett., 1996, 37, 7095.
3 C.-M. Yu, S.-K. Yoon, H.-S. Choi and K. Baek, Chem. Commun., 1997,
763; C.-M. Yu, H.-S. Choi, S.-K. Yoon and W.-H. Jung, Synlett, 1997,
889.
of the adducts 8 was unambiguously established after conver-
sion to 6 by comparison of their specific rotations with that of
known alcohols.11 The absolute sense of the asymmetric
induction parallels previous observations on catalytic allyla-
IV
2–4
4 C.-M. Yu, S.-K. Yoon, K. Baek and J.-Y. Lee, Angew. Chem., 1998,
tions that employed the (S)-BINOL–Ti catalyst.
1
10, 2504; Angew. Chem., Int. Ed., 1998, 37, 2392.
For reviews, see: Y. Yamamoto and N. Asao, Chem. Rev., 1993, 93,
207; D. Hoppe, W. R. Roush and E. J. Thomas, in Stereoselective
The adducts 8 are readily amenable to further conversion
with electrophiles to give the useful synthetic intermediates,
dienyl alcohols, with retention of enantiopurity, as described in
Scheme 2. For example, the alcohol 6 was obtained from the
5
2
Synthesis, Vol. 3, ed. G. Helmchen, R. W. Hoffmann, J. Mulzer and E.
Schaumann, Thieme, Stuttgart, 1996, pp. 1357–1602; M. Santell and
J.-M. Pons, Lewis Acids and Selectivity in Organic Chemistry, CRC
Press, New York, 1996, pp. 91–18; J. A. Marshall, Chem. Rev., 1996,
96, 31.
reaction of 8 (R = PhCH
isolated yield (a 4:1 mixture of aqueous HF and HCl at 0 °C in
THF). Treatment of 8 (R = PhCH CH ) with bromine (1.1
equiv.) in the presence of pyridine (5 equiv.) in CH
2 2
CH ) with acidic media in 78%
2
2
2
Cl
2
at 278
6 For example, see: B. M. Trost and H. Urabe, J. Am. Chem. Soc., 1990,
12, 4982.
1
7
H. J. Reich, I. L. Reich, K. E. Yelm, J. E. Holladay and D. Gschneidner,
J. Am. Chem. Soc., 1993, 115, 6625; H. J. Reich, K. E. Yelm and I. L.
Reich, J. Org. Chem., 1984, 49, 3438.
HO
R
H
H
Br
HO
R
H
HO
R
H
i
ii
8 G. E. Keck, K. H. Tarbet and L. S. Geraci, J. Am. Chem. Soc., 1993, 115,
8
2
467; G. E. Keck and D. Krishnamurthy, J. Am. Chem. Soc., 1995, 117,
363; G. E. Keck and D. Krishnamurthy, Org. Synth., 1997, 75, 12.
SiMe3
9
H. Mastalerz, J. Org. Chem., 1984, 49, 4092.
6
8
9
1
0 A. Ogawa and D. P. Curran, J. Org. Chem., 1997, 62, 450.
Scheme 2 Reagents and conditions: i, aq. HF/HCl (4:1), 0 °C, THF (R =
PhCH CH , 78%; R = C 13, 81%; R = Ph, 68%); ii, Br (1.1 equiv.),
pyridine (5 equiv.), 278 °C, 1 h, CH Cl , then TBAF, THF (R
PhCH CH , 71%; R = C 13, 74%).
11 For the dienylboration using stoichiometric homoallenylborane, see: R.
2
2
6
H
2
Soundararajan, G. Li and H. C. Brown, J. Org. Chem., 1996, 61, 100.
2
2
=
2
2
6
H
Communication 8/07940D
2750
Chem. Commun., 1998, 2749–2750