New Chiral Bis-Titanium(IV) Catalyst with Dibenzofuran Spacer for Catalytic Asymmetric Allylation of Aldehydes and Aryl Ketones

Full text of DOI:10.1002/1615-4169(20010129)343:1<57::AID-ADSC57>3.0.CO;2-O

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New Chiral Bis-Titanium(IV) Catalyst
with Dibenzofuran Spacer for Catalytic
Asymmetric Allylation of Aldehydes
and Aryl Ketones
a
b
a,b
Hideo Hanawa, Satoshi Kii, Keiji Maruoka *
a
Department of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
Phone and Fax: +81-75-7 53-40 41; e-mail: maruoka@kuchem.kyoto-u.ac.jp
b
Department of Chemistry, Graduate School of Science, Hokkaido University, Sapporo 060-0810, Japan
Received July 5, 2000, Accepted October 14, 2000
Catalytic asymmetric al-
lylation of aldehydes has
been considered as one
of the most fundamental
The requisite spacers,
4,6-bis(tritylamino)di-
benzofuran, 2,2'-bis(trityl-
aminophenyl) ether, and
Keywords: titanium; allylation; asymmetric cata-
lysis; homogeneous catalysis; Lewis acids
and important synthetic operations in asymmetric 4,5-bis(tritylamino)-9,9-dimethylxanthene can be
[
1,2]
synthesis,
and a number of catalytic procedures easily prepared from commercially available diben-
[
3±6]
have recently been elaborated for this purpose.
zofuran, diphenyl ether, and 9,9-dimethylxanthene,
However, previously reported catalytic allylation pro- respectively, by the following sequence: (i) treatment
cesses generally exhibited less satisfactory results in of the diphenyl ether derivatives with BuLi/TMEDA
enantioselectivity (~90% ee) in the case of cinnamal- (3 equiv) in ether/THF and subsequent addition of p-
dehyde. In this context, we were interested in the pos- TsN (60±77%); (ii) reduction of the bis-azides with
3
sibility of introducing a new type of metal catalyst to LiAlH in THF (85±95%); (iii) tritylation of diamines
4
improve the enantioselectivity in the asymmetric with NaH/TrBr (2.4 equiv) in THF (35±94%). Then,
allylation of cinnamaldehyde with allyltributyltin. the series of chiral bis-Ti(IV) catalysts 1±3 is synthe-
Herein we report the design of a new, chiral bis-Ti(IV) sized by mixing of these spacers with Ti(OiPr)4
complex of the type 1, and its utilization for the enan- (20 mol %) in CH Cl at room temperature for 1 h
2
2
tioselective allylation of aldehydes with allyltributyl- and subsequent treatment with (S)-binaphthol
tin as illustrated in Scheme 1. In addition, this catalyst (20 mol %) at room temperature for 10 h. The chiral
is also applicable to the catalytic, enantioselective efficiency of the bis-Ti(IV) catalysts 1±3 thus obtained,
allylation of aryl ketones.
was evaluated by the enantioselective allylation of
cinnamaldehyde, a rather tough substrate for con-
[
3±6]
ventional catalytic procedures.
Thus, reaction of
cinnamaldehyde 4 (R = CH=CHPh) with allyltributyl-
tin (1.1 equiv) under the influence of in situ generated
chiral bis-Ti(IV) catalyst 1 (10 mol %) in CH Cl at
2
2
0
5
°C for 10 h gave rise to 1-phenyl-1,5-hexadien-3-ol
[7,8]
(R = CH=CHPh) in 83% yield with 96% ee.
In a
similar manner, the chiral bis-Ti(IV) catalysts 2 and 3
gave comparable results (85%, 96% ee with 2; 81%,
9
6% ee with 3), as indicated in Table 1. Notably, both
the reaction rate and the enantioselectivity of the ally-
lation are dramatically lowered (e. g., 8% and 85% ee
for cinnamaldehyde) under similar reaction condi-
tions with a chiral mono-Ti(IV) complex 6 derived
from Ti(OiPr) , (S)-binaphthol, and 4-(tritylamino)di-
4
benzofuran as monodentate ligand (each 10 mol %).
The chiral mono-Ti(IV) complex 7 (10 mol %) also
gave less satisfactory result (17% and 92% ee for cin-
namaldehyde).
Scheme 1. Catalytic asymmetric allylation of aldehyde 4
with allyltributyltin in the presence of the chiral bis-Ti(IV)
complexes 1±3 [L = ((S)-binaphthoxy)(OiPr) ]
4 2
Adv. Synth. Catal. 2001, 343, No. 1
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57

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Although the exact reaction mechanism is not clear
at present, one possibility involves the simultaneous
coordination of two Ti atoms to a carbonyl oxygen,
thereby allowing the double activation of the alde-
[
9,10]
hyde carbonyls.
Such a double coordination phe-
nomenon of the bis-Ti(IV) catalyst 1 can probably be
deduced from the difference NOE measurement with
trans-4-methoxy-3-buten-2-one at low temperature
(
±20 °C), where the enone conformation around the
Other selected examples are included in Table 1. The
chiral bis-Ti(IV) catalyst 1 generally exhibits higher
reactivity than the analogues 2 and 3 (entries 4±6 and
single bond can be determined. The free trans-4-
methoxy-3-buten-2-one exists in both s-cis and s-trans
conformations, (A) and (B), since irradiation of the
7±9).
[a]
Table 1. Asymmetric allylation of aldehydes with allyltributyltin catalyzed by chiral bis-Ti(IV) complexes 1±3
[b]
[c]
[d]
entry
aldehyde
catalyst
conditions (°C, h)
0, 10
% yield
83
% ee (config)
1
2
3
4
5
6
7
PhCH=CHCHO
1
2
3
1
2
3
1
96 (S)
96 (S)
96 (S)
98 (S)
97 (S)
97 (S)
º
0, 10
85
º
0, 10
81
PhCHO
0, 2.5
94
º
º
0, 2.5
67
0, 2.5
71
[e]
0, 10
96
99 (S)
[
[
[
e]
e]
f]
8
9
º
º
2
3
1
1
0, 10
0, 10
0, 3
81
84
90
88
98 (S)
98 (S)
97 (S)
96
1
1
0
1
2 2
PhCH CH CHO
0, 8
[
a]
Unless otherwise noted, the reaction of aldehyde and Bu
3
2 2
SnCH CH=CH (1.1 equiv) was carried out in the presence of
1
0 mol % of chiral bis-Ti(IV) catalysts 1±3 in CH Cl under the given reaction conditions.
Isolated yield.
Determined by HPLC analysis using Chiralcel OD and OJ.
Determined by comparison of the sign of optical rotation with reported values. See ref.
Correlated to (S)-5 (R = Ph) (entries 4±6) by debromination of 5 (R = p-bromophenyl) with BuLi in ether.
2 2 2
Correlated to (S)-5 (R = CH=CHPh) (entries 1±3) by the catalytic hydrogenation of 5 (R = CH CH Ph) with Pd/C and H to
2 2
[
[
[
[
[
b]
c]
d]
e]
f]
[4b]
1
5
-phenyl-3-hexanol.
8
Adv. Synth. Catal. 2001, 343, 57±60

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CH C=O protons resulted in moderate NOE to both a-
analytical HPLC analysis [Daicel Chiralcel OD, hexane/
iPrOH = 30 : 1, flow rate = 0.5 mL/min, tR = 21.48 min ((R)-
isomer), tR = 26.21 min ((S)-isomer)] in comparison with
3
and b-methoxyvinyl protons. On complexation with
the mono-Ti(IV) Lewis acid 6, irradiation of the
[4b]
the racemic and authentic samples.
CH C=O protons again resulted in similar NOE to
3
both a- and b-methoxyvinyl protons. This result im-
plies that both s-cis and s-trans conformers, (C) and
(
D) exist in a similar ratio to the free enone in solu- Acknowledgments
tion. In contrast, however, in the bis-Ti(IV) 1/enone
complex, irradiation of the methyl proton of the
enone resulted in moderate NOE to only the b-proton
of the trans-methoxyvinyl group, implying the exist-
ence of the s-trans conformer (E) predominantly be-
cause of the double coordination.
The present approach can be successfully applied
to the catalytic, enantioselective allylation of aryl ke-
tones,
This work was supported by a Grant-in-Aid for Scientific Re-
serarch on Priority Areas (No. 706: Dynamic Control of
Stereochemistry) from the Ministry of Education, Science,
Sports and Culture. H. H. thanks the Japan society for the
Promotion of Science for Young Scientists for Research Fel-
lowships.
[
11]
where we utilized tetraallyltin as a more ef-
fective allylation agent than allyltributyltin. For ex- References
ample, treatment of acetophenone 8 (R = Ph, R' = Me)
with tetraallyltin (1.5 equiv) under the influence
of in situ generated chiral bis-Ti(IV) catalyst 1
[
1] Reviews: (a) R. Noyori, Asymmetric Catalysis in Organ-
ic Synthesis, Wiley, New York, 1993, p 1; (b) K. Maruo-
ka, H. Yamamoto in Catalytic Asymmetric Synthesis
(
30 mol %) in CH Cl at room temperature for 2.5 h
2 2
(Ed.: I. Ojima), VCH, New York, 1993, p 413; (c) K. Mi-
gave rise to (S)-2-phenyl-4-penten-2-ol 9 (R = Ph,
kami in Advance in Catalytic Process (Ed.:
M. P. Doyle), JAI: Greenwich, 1995, p 1; (d) A. H. Ho-
veyda, J. P. Morken, Angew. Chem. Int. Ed. 1996, 35,
[
12,13]
R' = Me) in 95% yield with 90% ee.
Under simi-
lar conditions, methyl b-naphthyl ketone 8 (R = b-Np,
R' = Me) was transformed to (S)-2-b-naphthyl-4-pen-
ten-2-ol 9 (R = b-Np, R' = Me) in 98% yield with
1
262; (e) A. Yanagisawa in Comprehensive Asymmetric
Catalysis (Eds.: E. N. Jacobsen, A. Pfaltz, H. Yamamo-
to), Springer: Berlin, 1999, p 965; (f) S. E. Denmark,
N. G. Almstead in Modern Carbonyl Chemistry (Ed.:
J. Otera), Wiley-VCH: Weinheim, 2000, p 299; (g) S. R.
Chemler, W. R. Roush in Modern Carbonyl Chemistry
[
14]
9
2% ee (Scheme 2).
(
Ed.: J. Otera), Wiley-VCH: Weinheim, 2000, p 403.
2] (a) Y. Yamamoto, N. Asao, Chem. Rev. 1993, 93, 2207;
b) D. Hoppe, W. R. Roush, E. J. Thomas in Stereoselec-
[
(
Scheme 2.
tive Synthesis, Vol. 3 (Eds.: G. Helmchen, R. W. Hoff-
mann, J. Mulzer, E. Schaumann), Thieme, Stuttgart,
1
996, p 1357.
[3] CAB complex: (a) K. Furuta, M. Mouri, H. Yamamoto,
Experimental Section
Synlett 1991, 561; (b) J. A. Marshall, Y. Tang, Synlett
1
992, 653; (c) K. Ishihara, M. Mouri, Q. Gao, T. Maru-
Catalytic Asymmetric Allylation of Benzaldehyde with
Allyltributyltin in the Presence of Bis-Ti(IV) Catalyst 1
A solution of 4,6-bis(tritylamino)dibenzofuran (341.4 mg,
yama, K. Furuta, H. Yamamoto, J. Am. Chem. Soc.
1993, 115, 11490.
[4] BINOL/Ti(IV) complex: (a) S. Aoki, K. Mikami, M. Te-
0
.5 mmol) in CH
then treated with Ti(OiPr)
perature under argon. After 1 h, (S)-BINOL (286.3 mg,
.0 mmol) was added at room temperature, and the mixture
2
Cl
2
(15 mL) was carefully degassed and
rada, T. Nakai, Tetrahedron 1993, 49, 1783; (b) A. L.
(295 lL, 1.0 mmol) at room tem-
Costa,
M. G. Piazza,
E. Tagliavini,
C. Trombini,
4
A. Umani-Ronchi, J. Am. Chem. Soc. 1993, 115, 7001;
(c) G. E. Keck, K. H. Tarbet, L. S. Geraci, J. Am. Chem.
Soc. 1993, 115, 8467; (d) G. E. Keck, L. S. Geraci, Tetra-
hedron Lett. 1993, 34, 7827; (e) G. E. Keck, D. Krishna-
murthy, M. C. Grier, J. Org. Chem. 1993, 58, 6543;
(f) G. E. Keck, D. Krishnamurthy, X. Chen, Tetrahe-
dron Lett. 1994, 35, 8323; (g) J. W. Faller, D. W. Sams,
X. Liu, J. Am. Chem. Soc. 1996, 118, 1217; (h) D. R.
Gauthier, Jr, E. M. Carreira, Angew. Chem. Int. Ed.
1996, 35, 2363; (i) S. Weigand, R. Br uÈ ckner, Chem. Eur.
J. 1996, 2, 1077; (j) C.-M. Yu, H.-S. Choi, W.-H. Jung,
S.-S. Lee, Tetrahedron Lett. 1996, 37, 7095; (k) C.-M.
Yu, H.-S. Choi, W.-H. Jung, H.-J. Kim, J. Shin, Chem.
Commun. 1997, 761; (l) C.-M. Yu, H.-S. Choi, S.-K.
Yoon, W.-H. Jung, Synlett 1997, 889; (m) J. A. Marshall,
Chemtracts 1997, 10, 649; (n) G. E. Keck, T. Yu, Org.
1
was stirred for 10 h. The solution was then cooled to ±15 °C,
and treated sequentially with benzaldehyde (508 lL,
5
The whole mixture was allowed to warm to 0 °C and stirred
for 2.5 h. The reaction mixture was quenched with saturated
NaHCO
were dried over Na
purification of the residue by column chromatography on
silica gel (ether/hexane = 1 : 4) gave (S)-1-phenyl-3-buten-
mmol) and allyltributyltin (1.71 mL, 5.5 mmol) at ±15 °C.
3
, and extracted with CH
2 2
Cl . The organic extracts
2
SO . Evaporation of the solvents and
4
1
4
-ol as a colorless oil; yield: 696.5 mg (94%). (S)-BINOL and
,6-bis(tritylamino)dibenzofuran were recovered in 89%
[
15]
and 74% yields, respectively.
The absolute configuration and enantiomeric purity of 1-
phenyl-3-buten-1-ol were determined to be S and 98% ee by
Adv. Synth. Catal. 2001, 343, 57±60
59

asc.wiley-vch.de
Lett. 1999, 1, 289; (o) E. Brenna, L. Scaramelli, S. Ser-
ra, Synlett 2000, 357.
5] BINAP/AgOTf complex: A. Yanagisawa, H. Nakashima,
A. Ishiba, H. Yamamoto, J. Am. Chem. Soc. 1996, 118,
(c) T. Ooi, A. Saito, K. Maruoka, Tetrahedron Lett.
1998, 39, 3745; (d) T. Ooi, T. Miura, K. Maruoka, An-
gew. Chem. Int. Ed. 1998, 37, 2347.
[
[
1
3
[10] Such activation is also observed by C NMR spectro-
4
723.
scopy using 2,6-dimethyl-c-pyrone as carbonyl sub-
1
3
6] Bis(oxazoline)/Zn(II) or Rh(II) complex: (a) P. G. Coz-
zi, P. Orioli, E. Tagliavini, A. Umani-Ronchi, Tetrahe-
dron Lett. 1997, 38, 145; (b) Y. Motoyama, H. Narusa-
wa, H. Nishiyama, Chem. Commun. 1999, 131.
strate:
C NMR (CDCl
3
at 20 °C): d = 165.41 (free
pyrone b-carbons); 166.31 (pyrone b-carbons of the
1 : 1 2,6-dimethyl-c-pyrone/mono-Ti(IV) 6 complex),
167.46 (pyrone b-carbons of the 1 : 1 2,6-dimethyl-c-
pyrone/bis-Ti(IV) 1 chelation complex), 166.39 (pyr-
one b-carbons of the 2 : 1 2,6-dimethyl-c-pyrone/bis-
Ti(IV) 1 chelation complex).
[
7] The absolute configuration of the homoallylic alcohol
5
(R = CH=CHPh) was determined to be S by correla-
[
4b]
tion to the authentic sample; see ref.
.
[
8] Our initial attempt to use chiral bis-Ti(IV) catalysts of
type 1 (10 mol %) from the parent 4,6-diamino-
dibenzofuran or 4,6-bis(ethylamino)dibenzofuran as
[11] S. Casolari, D. D'Addario, E. Tagliavini, Org. Lett.
1999, 1, 1061.
[12] Attempted allylation of acetophenone
8 (R = Ph,
spacers by combining Ti(OiPr)
naphthol turned out to be less satisfactory [15%
90% ee) or 12% yield (85% ee), respectively, at 0 ëC
4
and chiral (S)-bi-
R' = Me) with allyltributyltin (1.5 equiv) in the pre-
sence of in situ generated chiral bis-Ti(IV) catalyst 1
(30 mol %) in CH Cl gave none of 2-phenyl-4-penten-
2 2
(
for 10 h] in the asymmetric allylation of cinnamalde-
hyde 4 (R = CH=CHPh) with allyltributyltin. Introduc-
tion of bulky silyl moieties on the amino groups in
2-ol 9 (R = Ph, R' = Me) with recovery of most of the
acetophenone under similar conditions.
[13] M. Ishizaki, K. Soai, S. Yokoyama, Chem. Lett. 1987,
341.
4
,6-diaminodibenzofuran in order to make two Ti
atoms closely aligned by their steric repulsion re-
sulted in enhancement of reactivity of the asymmetric
allylation. Indeed, the bis-Ti(IV) catalyst (10 mol %) of
type 1 derived from 4,6-bis(t-butyldiphenylsilylami-
[14] In the asymmetric allylation of ketones with tetraallyl-
tin, the enantioselectivity tends to be lowered by de-
creasing the amount of the bis-Ti(IV) catalyst 1 [e. g.,
90% (30 mol % 1); 76% (20 mol % 1); 66% (10 mol %
1) with acetophenone], probably because of the unde-
sired intervention of the in situ generated, more reac-
tive triallyltin alkoxide (or diallyltin dialkoxide) than
tetraallyltin during the course of the ketone allylation.
[15] 6-Amino-4-(tritylamino)dibenzofuran was also recov-
ered in 17% yield.
no)dibenzofuran, Ti(OiPr)
forded 5 (R = CH=CHPh) in 34% yield (93% ee) (at
°C for 10 h).
4
, and (S)-binaphthol af-
0
[
9] (a) T. Ooi, M. Takahashi, K. Maruoka, J. Am. Chem.
Soc. 1996, 118, 11307; (b) N. Asao, S. Kii, H. Hanawa,
K. Maruoka, Tetrahedron Lett. 1998, 39, 3729;
6
0
Adv. Synth. Catal. 2001, 343, 57±60