High-pressure enantioselective allylation of aldehydes catalyzed by (salen)chromium(III) complexes

Article abstract of DOI:10.1055/s-2004-836067

The enantioselective addition of allyltributyltin to simple aldehydes (2a-1), catalyzed by chiral (salen)Cr(III) complexes 1, has been studied. The reaction proceeds smoothly with low loading (1-2 mol%) of (salen)Cr(III)BF ₄ (1a) and allyltribu

Full text of DOI:10.1055/s-2004-836067

LETTER
227
High-Pressure Enantioselective Allylation of Aldehydes Catalyzed by
(Salen)Chromium(III) Complexes
H
igh-Pressure
i
E
nanti
o
oselective
A
l
lylatio
r
n of
A
ldehydesKwiatkowski,a Janusz Jurczak*a,b
a
Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland
Department of Chemistry, Warsaw University, Pasteura 1, 02-093 Warsaw, Poland
Fax +48(22)6326681; E-mail: jurczak@icho.edu.pl
b
Received 13 October 2004
butyldimethylsilyloxyacetaldehyde.15 Unfortunately, the
(salen)Cr(III)BF4 complexes, which are weak Lewis acids
compared with typical catalysts used for this type of reac-
tion, do not work well at room temperature, under atmo-
Abstract: The enantioselective addition of allyltributyltin to simple
aldehydes (2a–l), catalyzed by chiral (salen)Cr(III) complexes 1,
has been studied. The reaction proceeds smoothly with low loading
(1–2 mol%) of (salen)Cr(III)BF4 (1a) and allyltributyltin under
high-pressure conditions (10 kbar) in good yield and ee values in the spheric pressure, with simple aldehydes and allyl-
range of 35–79%.
tributyltin (Scheme 1, Figure 2), and afford homoallylic
alcohols usually with low yield. We succeeded, however,
when high-pressure conditions (10 kbar) were applied.16
Over 20 years ago Yamamoto et al.17 found that allylic
stannanes react with aldehydes at room temperature under
high pressure (10 kbar) without any catalyst. This proce-
Key words: aldehydes, allylstannane, asymmetric catalysis, high-
pressure technique, homoallylic alcohols, salen–chromium com-
plexes
Catalytic enantioselective allylation of aldehydes is one of dure is a mild method for the allylation of aldehydes,
the most important methods for preparing enantiomerical- which may be useful for preparation of the labile, thermal-
ly enriched secondary alcohols, and until now, many effi- ly unstable and acid-sensitive compounds. To our knowl-
cient methods for carrying out this reaction have been edge, this high-pressure methodology has not been used
developed,1 often using allylstannanes.2 Lewis acids are for enantioselective allylation. However, we found in the
typically used as chiral catalysts, and the most efficient literature some examples of diastereoselective allylation
are BINOL complexes with Ti(IV),3 and Zr(IV)4 as well of chiral aldehydes,17c,18 e.g. a-amino aldehydes.
as chiral acyloxy boranes derived from tartaric acid,5 BI-
NAP/Ag(I),6 and chiral bisoxazoline ligands with
Rh(III).7 Generally, most of these procedures require high
catalyst loading (10–20 mol%), as well as anhydrous,
sometimes even oxygen-free, reaction conditions.
N
O
N
O
N
O
N
O
Cr
X
Cr
Cl
In this work, we focused our attention on the application
of stable and readily available (salen)metal complexes
for allylation of aldehydes. The first application of
(salen)metal complexes for enantioselective allylation
was reported by Cozzi and Umani–Ronchi8 in the catalyt-
ic Nozaki–Hiyama–Kishi reaction with allylic halides
promoted by (salen)chromium complexes.8,9 Recently, we
published a paper dealing with enantioselective allyla-
tions of reactive aldehydes such as alkyl glyoxylates, us-
ing allyltributyltin, catalyzed by 1–2 mol% of
(salen)Cr(III)BF4 complexes (Figure 1, compound 1a),
leading to 2-hydroxypent-4-enoic acid esters with good
yield and enantioselectivities of 60–76%.10 The
(salen)chromium(III) complexes of type 1, introduced to
enantioselective catalysis by Jacobsen,11 are known to be
efficient catalysts for hetero-Diels–Alder reaction,12 as
well as for ring-opening of epoxides by trimethylsilyl
azide11 and for some other reactions.13 In our research
group, we also used these catalysts for the [4+2] cyclo-
addition of various 1,3-dienes to glyoxylates14 and tert-
1a) X = BF4
1b) X = Cl
1c
Figure 1 The (salen)chromium(III) complexes used
(1R,2R)-(salen)CrX
R
H
R
SnBu3
O
OH
2a–l
3a–l
Scheme 1 Allylation of aldehydes
As a model, we have chosen the reaction of furfural (2a)
with allyltributyltin19 in dichloromethane. The reaction
was very slow under ambient conditions (Table 1, entry 1)
leading, after three days, to the expected product having
56% ee, in ca. 10% yield. In such a situation, we decided
to optimize the reaction conditions. Increasing tempera-
ture up to 60 °C did not improve the yield satisfactory
even when the reaction was carried out without any sol-
vent. Addition of molecular sieves raised the yield up to
SYNLETT 2005, No. 2, pp 0227–0230
0
1.
0
2.
2
0
0
5
Advanced online publication: 10.12.2004
DOI: 10.1055/s-2004-836067; Art ID: G34904ST
© Georg Thieme Verlag Stuttgart · New York

228
P. Kwiatkowski, J. Jurczak
LETTER
Cl
56% to 67% (entries 3 and 4); the best results were ob-
tained in those reactions performed at pressures under 10
kbar.20 Unfortunately, addition of molecular sieves to the
reaction mixture under high-pressure conditions lowered
the ee (entry 5). Contrary to many known enantioselective
procedures, concentration of 2 mol% of catalyst is enough
in this method for effective allylation of furfural to afford
expected homoallylic alcohols in high yield of ca. 90%
(e.g. entry 4). For comparison, we carried out the analo-
gous reaction but without any catalyst, and the yield was
much lower (entry 6). This means that the (salen)CrBF4
complexes, which are rather weak Lewis acids, have a
strong influence on the rate of investigated reaction under
high-pressure conditions.
O
O
O
O
O
Me
O
O
2a
2b
2c
2g
2d
2h
Cl
O2N
O
O
O
O
2e
2f
O
O
O
TritylO
2j
2i
2k
2l
Figure 2 Aldehydes used for allylation
The next stage of our study was an attempt to optimize the
reaction conditions at a pressure of under 10 kbar. We in-
vestigated several factors such as loading of the catalyst,
solvents, additives, concentration of the aldehyde. Load-
46% but the results were still not satisfactory (entry 2). As
already mentioned, we succeeded under high-pressure
conditions. High pressure not only accelerated the reac-
tion rate but also increased the enantioselectivity from
Table 1 Results of the Model Reaction of Furfural (2a) with Allyltributyltina
(1R,2R)-(salen)CrX
SnBu3
O
+
O
O
OH
2a
3a
Entry
Catalyst
Mol% of catalyst Concentration of Pressure (bar)
Solvent
Time (h)
Yield (%)b ee (%)c
2a (mol/L)
1
2
1a
2
1.4
1.4
0.5
0.5
0.5
0.5
0.5
0.5
0.5
1.0
1.5
0.5
0.5
0.5
0.5
0.5
0.5
1
1
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CHCl3
72
72
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
10
46
71
91
95
17
94
82
69
94
89
91
84
56
67
81
92
56
58
62
67
52
0
1a
2 + MS 4 Å
3
1a
2
7000
4
1a
2
10000
10000
10000
10000
10000
10000
10000
10000
10000
10000
10000
10000
10000
10000
5
1a
2 + MS 4 Å
6
No cat.
1a
–
7
5
68
64
61
68
67
66
67
71
66
20
60
8
1a
1
9
1a
0.5
2
10
11
12
13
14
15
16
17d
1a
1a
1
1a
2
1a
2
(CH2Cl)2
i-PrNO2
CH2Cl2
CH2Cl2
CH2Cl2
1a
2
1b
1c
2
2
1a
2
a High-pressure reactions were carried out in a 2 mL Teflon ampoule using 1.1 equiv of allyltributyltin at 20 °C.
b Yield was determined by GC.
c The ee was determined by GC on capillary chiral b-dex 120 column.
d Instead of allyltributyltin, 1.1 equiv of allyltrimethyltin was used.
Synlett 2005, No. 2, 227–230 © Thieme Stuttgart · New York

LETTER
High-Pressure Enantioselective Allylation of Aldehydes
229
ing of the catalyst in a range of 5–0.5 mol% has a slight Table 2 Enantioselective Allylation of Aldehydes Catalyzed by
(1R,2R)-1aa
influence on enantioselectivity (compare entries 4 and 7–
9). What is very promising in this method, even 0.5 mol%
Entry
1
Aldehydeb
Yield (%)c
ee (%)d
67 (R)
61
of 1a gives quite good results (entry 9). Allylation pro-
ceeds, without lowering the ee, at higher concentration of
the aldehyde (entry 10), even when the 2 mL Teflon am-
poule was filled with 3 mmol of 2a, 1 mol% of 1a, 1 mL
of allyltributyltin and made up with CH2Cl2 (entry 11).
The possibility of using concentrated reaction mixtures is
a great advantage because of limitation of the volume of
high-pressure chambers (the average volume is 50 mL).
Unfortunately, the reaction does not work well without
solvent for furfural 2a and other aldehydes, which are
insoluble in allyltributyltin.
2a
2b
2c
2d
2e
2f
89
79
82
81
85
83
52
86
82
70
84
86
2
3
55 (R)
60
4
5
68
6
68
7
2g
2h
2i
75 (S)
68
Besides dichloromethane, of the solvents studied, CHCl3,
1,2-dichloroethane, CH2Cl2–hexane (1:1), and i-PrNO2
also worked well (e.g. entries 12–14). The latter of these
solvents gave the highest ee, but the yield was lower.
8
9
79 (R)
35
10
11
12
2j
We have also tested the applicability of two other chromi-
um complexes for this reaction. The commercially avail-
able complex 1b, with a chloride counter-ion, catalyzed
the reaction practically with the same enantioselectivity
(see entries 4 and 15), but the reaction yield was lower.
We have also checked the chromium chloride complex 1c
having another widely used chiral 1,2-diamines, e.g., 1,2-
diphenylethylenediamine, but the enantioselectivity was
2k
2l
65 (R)
53 (R)
a Conditions: 1 mmol of the aldehyde, 2 mol% of (1R,2R)-
(salen)CrBF4 (1a), 1.1 mmol of allylSnBu3 in CH2Cl2 in 2 mL Teflon
ampoule; 10 kbar at 20 °C for 24 h.
b Structures of aldehydes are shown in Figure 2.
c Isolated yield.
much lower (entry 16). More reactive allyltrimethyltin d The ee was determined by GC on a capillary chiral b-dex 120
can also be used instead of allyltributyltin, however, the
column (see ref.21).
ee was slightly lower (entry 17).
The next stage of the study was an attempt to show useful-
ness of the high-pressure method in reaction with other
aldehydes. Table 2 summarizes the results obtained for
cially available (salen)CrCl (1b) can also be used as an ef-
ficient catalyst. According to our knowledge, this is the
the reactions of a variety of aromatic and aliphatic alde-
first example of enantioselective allylation of aldehydes
hydes with 1.1 equivalent of allyltributyltin, in the pres-
under high-pressure conditions. Even though high-pres-
sure equipment is not common in synthetic laboratories
and rather expensive, our approach constitutes a synthetic
method of choice having some advantages: requires small
amount of readily available stable and recoverable cata-
lyst and can be carried out for concentrated reaction mix-
tures in reagent grade solvents. What is more, the oxygen-
free conditions are not necessary. On the other hand, we
ence of 2 mol% of 1a. The obtained enantiomeric
excesses for aromatic aldehydes 2a–f range from 55–68%
and the yields are 79% and higher. This methodology
works well also for aliphatic aldehydes (e.g. 2g–i), how-
ever, sometimes the yields are lower. The lowest ee was
obtained for a bulky pivalaldehyde 2j (entry 10). With
good yield and moderate ee (65% and 53%, respectively),
the allylation reaction also works for a,b-unsaturated
cinnamaldehyde 2k (entry 11) and the glycolaldehyde
derivative 2l (entry 12).
show how low active catalyst under normal conditions can
be successfully applied for reactions accelerated under
high-pressure conditions. Further studies to improve the
The enantiomeric excess values were determined by GC enantioselectivity, mainly by modification of the structure
employing a capillary chiral b-dex 120 column.21 In some of catalysts, are underway.
cases (Table 2, entries 1, 3, 7, 9, 11, and 12), we con-
firmed the absolute configuration of the obtained homo-
allylic alcohols via measurement of optical rotation and
References
(1) For a recent review, see: Denmark, S. E.; Fu, J. Chem. Rev.
2003, 103, 2763.
(2) Gung, B. W. In Organic Reactions, Vol. 64; J. Wiley and
comparison with the literature data. In all cases when
chromium complex (1R,2R)-1a was used, we observed
the same direction of asymmetric induction.
Sons: New York, 2004, Chap. 1.
In conclusion, we have developed a new and mild method
for enantioselective allylation of aldehydes, catalyzed by
1–2 mol% of readily available (salen)CrBF4 (1a) afford-
ing in good yield homoallylic alcohols having at this stage
of our studies moderate to good ee values. The commer-
(3) (a) Costa, A. L.; Piazza, M. G.; Tagliavini, E.; Trombini, C.;
Umani-Ronchi, A. J. Am. Chem. Soc. 1993, 115, 7001.
(b) Keck, G. E.; Tarbet, K. H.; Geraci, L. S. J. Am. Chem.
Soc. 1993, 115, 8467. (c) Aoki, S.; Mikami, K.; Terada, M.;
Nakai, T. Tetrahedron 1993, 49, 1783.
Synlett 2005, No. 2, 227–230 © Thieme Stuttgart · New York

230
P. Kwiatkowski, J. Jurczak
LETTER
(4) (a) Bedeschi, P.; Casolari, S.; Costa, A. L.; Tagliavini, E.;
Umani-Ronchi, A. Tetrahedron Lett. 1995, 36, 7897.
(b) Casolari, S.; Cozzi, P. G.; Orioli, P. A.; Tagliavini, E.;
Umani-Ronchi, A. Chem.Commun. 1997, 2123.
(c) Hanawa, H.; Kii, S.; Asao, N.; Maruoka, K. Tetrahedron
Lett. 2000, 41, 5543. (d) Kurosu, M.; Lorca, M.
Tetrahedron Lett. 2002, 43, 1765.
(5) Furuta, K.; Mouri, M.; Yamamoto, H. Synlett 1991, 561.
(6) Yanagisawa, A.; Nakashima, H.; Ishiba, A.; Yamamoto, H.
J. Am. Chem. Soc. 1996, 118, 4723.
(15) Malinowska, M.; Kwiatkowski, P.; Jurczak, J. Tetrahedron
Lett. 2004, 45, 7693.
(16) (a) High Pressure Chemical Synthesis; Jurczak, J.;
Baranowski, B., Eds.; Elsevier: New York, 1989.
(b) Organic Synthesis at High Pressure; Matsumato, K.;
Acheson, R. M., Eds.; Wiley: New York, 1991.
(c) Chemistry under Extreme or Non-Classical Conditions;
van Eldik, R.; Hubbard, C. D., Eds.; Wiley: New York,
1997.
(17) (a) Yamamoto, Y.; Maruyama, K.; Matsumoto, K. J. Chem.
Soc., Chem. Commun. 1983, 489. (b) Yamamoto, Y.;
Yatagai, H.; Ishihara, Y.; Maeda, N.; Maruyama, K.
Tetrahedron 1984, 40, 2239. (c) Yamamoto, Y.; Komatsu,
T.; Maruyama, K. J. Organomet. Chem. 1985, 285, 31.
(d) Yamamoto, Y.; Saito, K.-i. J. Chem. Soc., Chem.
Commun. 1989, 1676.
(7) Motoyama, Y.; Narusawa, H.; Nishiyama, H. Chem.
Commun. 1999, 131.
(8) Bandini, M.; Cozzi, P. G.; Melchiorre, P.; Umani-Ronchi, A.
Angew. Chem. Int. Ed. 1999, 38, 3357.
(9) (a) Bandini, M.; Cozzi, P. G.; Umani-Ronchi, A. Angew.
Chem. Int. Ed. 2000, 39, 2327. (b) Bandini, M.; Cozzi, P.
G.; Umani-Ronchi, A. Tetrahedron 2001, 57, 835.
(c) Bandini, M.; Cozzi, P. G.; Melchiorre, P.; Morganti, S.;
Umani-Ronchi, A. Org. Lett. 2001, 3, 1153. (d) Berkessel,
A.; Menche, D.; Sklorz, C. A.; Schröder, M.; Paterson, I.
Angew. Chem. Int. Ed. 2003, 42, 1032. (e) Lombardo, M.;
Licciulli, S.; Morganti, S.; Trombini, C. Chem. Commun.
2003, 1762. (f) Bandini, M.; Cozzi, P. G.; Licciulli, S.;
Umani-Ronchi, A. Synthesis 2004, 409.
(18) Cokley, T. M.; Isaacs, N. S.; McCluskey, A.; Young, D. J.
Main Group Met. Chem. 1997, 20, 581.
(19) Halligan, N. G.; Blaszczak, L. C. Org. Synth. 1990, 68, 104.
(20) General Procedure for the High-Pressure Allylation:
In a 2 mL Teflon ampoule were placed (salen)CrBF4 (2a,
usually 13.7mg, 2 mol%), ca. 1 mL of solvent (usually
CH2Cl2), followed by aldehyde (usually 1 mmol) and
allyltributyltin (1.1 equiv). Finally, the ampoule was made
up with solvent, closed and placed in a high-pressure vessel,
and pressure was slowly increased to 10 kbar at 20 °C. After
stabilization of pressure, the reaction mixture was kept under
these conditions for 24 h. After decompression, the reaction
mixture was diluted with wet Et2O, and dried over MgSO4.
After evaporation of solvents, the residue was
chromatographed on a silica gel column using hexane–
EtOAc. All liquid aldehydes were distilled prior to use.
(21) Enantioselectivity of homoallylic alcohols 3a–l was
determined by GC employing a capillary chiral b-dex 120
column. Alcohols 3c,k were analyzed directly, 3a,b,d–h,j as
their O-trimethylsilyl derivatives, 3i as a trifluoroacetate and
3l as a isopropylidene derivative of pent-4-ene-1,2-diol.
(10) Kwiatkowski, P.; Chaladaj, W.; Jurczak, J. Tetrahedron
Lett. 2004, 45, 5343.
(11) (a) Martínez, L. E.; Leighton, J. L.; Carsten, D. H.; Jacobsen,
E. N. J. Am. Chem. Soc. 1995, 117, 5897. (b) Leighton, J.
L.; Jacobsen, E. N. J. Org. Chem. 1996, 61, 389.
(12) Schaus, S. E.; Brånalt, J.; Jacobsen, E. N. J. Org. Chem.
1998, 63, 403.
(13) For a review of applications of the(salen)Cr complexes in
asymmetric catalysis, see: (a) Bandini, M.; Cozzi, P. G.;
Umani-Ronchi, A. Chem. Commun. 2002, 919. (b) Larrow,
J. F.; Jacobsen, E. N. Top. Organomet. Chem. 2004, 6, 123.
(14) (a) Kwiatkowski, P.; Asztemborska, M.; Caille, J.-C.;
Jurczak, J. Adv. Synth. Catal. 2003, 506. (b) Kwiatkowski,
P.; Asztemborska, M.; Jurczak, J. Synlett 2004, 1755.
(c) Kwiatkowski, P.; Asztemborska, M.; Jurczak, J.
Tetrahedron: Asymmetry 2004, 15, 3189.
Synlett 2005, No. 2, 227–230 © Thieme Stuttgart · New York