Asymmetric Michael addition reactions of 2-silyloxyfurans catalyzed by binaphthyldiimine-Ni(II) complexes

Article abstract of DOI:10.1039/b402826k

N,N′-Bis(2-quinolylmethylene)-1,1′-binaphthyl-2, 2′-diamine-Ni(II) complex and analogous complexes were found to be efficient chiral Lewis acid catalysts for the asymmetric Michael addition reactions between 2-silyloxyfurans and 3-alkenoyl-2-oxazolidinones, for which asymmetric inductions of up to 97% ee were obtained.

Full text of DOI:10.1039/b402826k

Asymmetric Michael addition reactions of 2-silyloxyfurans catalyzed by
binaphthyldiimine–Ni(II) complexes†
Hiroyuki Suga,* Takeo Kitamura, Akikazu Kakehi and Toshihide Baba
Department of Chemistry and Material Engineering, Faculty of Engineering, Shinshu University, Wakasato,
Nagano 380-8553, Japan. E-mail: sugahio@gipwc.shinshu-u.ac.jp
Received (in Cambridge, UK) 24th February 2004, Accepted 15th April 2004
First published as an Advance Article on the web 17th May 2004
N,NA-Bis(2-quinolylmethylene)-1,1A-binaphthyl-2,2A-diamine–
Ni(II) complex and analogous complexes were found to be
efficient chiral Lewis acid catalysts for the asymmetric Michael
addition reactions between 2-silyloxyfurans and 3-alkenoyl-
2-oxazolidinones, for which asymmetric inductions of up to 97%
ee were obtained.
Ni(II) complexes (10 mol%) by stirring chiral BINIMs (BINIM-
DC, BINIM-OH, BINIM-DCOH, BININ-2NAP, or BINIM-2QN;
see Fig. 1) and Ni(ClO4)2·6H2O in CH2Cl2 for 6 h in the presence
of 4Å molecular sieves (MS 4A), the reaction was carried out at
225 °C in the presence of hexafluoro-2-propanol6 (HFIP, 1 equiv.)
for 1–7 h to afford Michael adduct 3a in 75% to quantitative yields
(Table 1, Entries 1–5). Among the BINIMs tested, the result for
(R)-BINIM-2QN was promising in terms of enantioselectivity
(82% ee, Entry 5). Substitution with a methyl or phenyl group at the
4-position on the quinoline rings of BINIM-2QN resulted in slight
increases in the enantioselectivities (Entries 10 and 17). The
investigation of the solvents (Entries 6, 7, and 11) revealed that
Chiral g-butenolides and their derivatives are common structural
subunits in natural products and biologically active compounds.1
Accordingly, the development of an efficient procedure for the
asymmetric synthesis of these compounds is an important objective
in organic syntheses. Recently, MacMillan has reported that an
organic catalyst, such as chiral imidazolidinone, was effective in
affording chiral g-butenolides in the asymmetric Michael addition
reactions between 2-silyloxyfurans and a,b-unsaturated aldehydes
with high syn- and enantioselectivties; the reaction was subse-
quently applied towards the synthesis of spiculisporic acid.2 Chiral
Lewis acids can also be expected to act as effective catalysts for the
synthesis of optically active g-butenolides via nucleophilic addition
reactions of 2-silyloxyfurans. In fact, several Mukaiyama aldol
reactions of 2-silyloxyfurans with carbonyl compounds promoted
by Lewis acids have been reported.3 However, only a few examples
of Michael addition reactions of 2-silyloxyfurans catalyzed by
chiral Lewis acids are known.4 These examples typically employed
3-crotonoyl-2-oxazolidinone as the Michael acceptor, and their
applications to other 2-silyloxyfuran derivatives and 3-alkenoyl-
2-oxazolidinones were not studied in detail. Herein, we report on
the use of Ni(II)-complexes of chiral N,NA-bis(2-quinolylmethy-
lene)-1,1A-binaphthyl-2,2A-diamine (BINIM-2QN) derivatives as
efficient chiral Lewis acid catalysts for the Michael addition
reactions of 2-silyloxyfuran and its derivatives with various
3-alkenoyl-2-oxazolidinones.5
Fig. 1 Structures of (R)-BINIMs.
Table 1 Michael addition reactions of silyloxyfuran 1 with oxazolidinone
2a catalyzed by chiral BINIM-Ni(II) complexesa
Time Temp. Yield eed
Entry BINIM
Additiveb Solvent MSc (h)
(°C)
(%)
(%)
Initially, several chiral binaphthyldiimines (BINIMs), in combi-
nation with Ni(ClO4)2·6H2O, were tested as chiral catalysts for the
reaction between 2-(trimethylsilyloxy)furan (1) and 3-acryloly-
2-oxazolidinone (2a) (Scheme 1). Following the preparation of the
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
DC
HFIP
HFIP
HFIP
HFIP
HFIP
HFIP
HFIP
PFP
CH2Cl2 4A
CH2Cl2 4A
CH2Cl2 4A
CH2Cl2 4A
CH2Cl2 4A
CHCl3 4A
1
7
3
1
1
1
225 75
225 quant
225 90
225 quant
225 94
225 92
225 66
225 84
225 90
225 98
225 82
225 13f
225 15g
225 96
225 87
225 90
225 99
225 93
225 11
225 89
225 87
2
34
210
32
82
84
55
85
89
84
86
22
69
85
83
91
84
91
41
91
91
OHe
DCOH
2NAP
2QN
2QN
2QN
2QN
2QN
4Me-2QN HFIP
4Me-2QN HFIP
4Me-2QN none
Toluene 4A 48
CH2Cl2 4A
CHCl3 4A
CH2Cl2 4A
CHCl3 4A
CH2Cl2 4A
1
2
1
1
2
2
1
1
1
1
1
PFP
4Me-2QN i-PrOH CH2Cl2 4A
4Me-2QN PhOH
4Me-2QN PFP
4Me-2QN PFP
CH2Cl2 4A
CH2Cl2 4A
CHCl3 4A
CH2Cl2 4A
CHCl3 4A
CHCl3 none 96
CHCl3 3A
CHCl3 5A
17h 4Ph-2QN HFIP
18h 4Ph-2QN PFP
19
4Ph-2QN PFP
20h 4Ph-2QN PFP
21h 4Ph-2QN PFP
1
1
a All reactions were carried out in the presence of chiral BINIM-Ni(II
)
Scheme 1 Michael addition reactions of 2-trimethylsilylfurans with
complexes (10 mol%). b One equiv. of the additive was used. c Thirty mg of
molecular sieves per 0.25 mmol of 2a were used. d Determined by HPLC.
e (S)-BINIM was used. f Double Michael addition product 4 was obtained in
49% yield. g Double Michael addition product 4 was obtained in 75% yield.
h The complexes were prepared for 2 h.
3-alkenoyl-2-oxazolidinones catalyzed by chiral BINIM-Ni(II
) com-
plexes.
† Electronic supplementary information (ESI) available: experimental
details. See http://www.rsc.org/suppdata/cc/b4/b402826k/
1414
C h e m . C o m m u n . , 2 0 0 4 , 1 4 1 4 – 1 4 1 5
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4

Table 2 Asymmetric Michael addition reactions of silyloxyfurans 1, 6, 8, and 10 with oxazolidinones 2a, 2b, and 2c.a
BINIM-4X- Additiveb
Time
(h)
Temp
(°C)
Yield
(%)
eec
(%)
Entry
1, 6, 8, 10
2
2QN
/Solvent
anti/syn
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
1
1
1
1
1
1
1
1
1
1
6
6
6
6
6
8
8
2b
2b
2b
2b
2b
2c
2c
2c
2c
2c
2a
2a
2b
2c
2c
2a
2c
2a
4H
4H
4Hd
4Med
4Phd
4H
PFP/CHCl3
HFIP/CHCl3
HFIP/CHCl3
HFIP/CH2Cl2
HFIP/CHCl3
HFIP/CH2Cl2
PFP/CHCl3
PFP/CHCl3
PFP/CHCl3
PFP/CHCl3
PFP/CHCl3
PFP/CHCl3
HFIP/CHCl3
HFIP/CHCl3
HFIP/CHCl3
PFP/CHCl3
HFIP/CHCl3
PFP/CHCl3
168
96
42
20
72
3
15
36
168
15
18
87
87
2
225
225
225
225
225
240
240
240
240
240
225
225
225
225
240
225
240
225
78
93
quant
95
89
98
97
93
80
93
84
75
82
95
97
quant
95
89
98 : 2
98 : 2
98 : 2
95 : 5
99 : 1
> 99 : 1
> 99 : 1
> 99 : 1
> 99 : 1
> 99 : 1
—
70
85
88
86
89
91
93
91
89
88
97
94
93
97
96
88
78
86
4H
4He
4Hf
4Me
4H
4Ph
4H
4H
4H
4H
—
99 : 1
> 99 : 1
> 99 : 1
—
91 : 9
—
2
6
55
21
4H
4H
10
a All reactions were carried out in the presence of chiral BINIM-Ni(II) complexes (10 mol%). b One equiv of the additive was used. c Determined by HPLC.
d Twenty mol% of the catalyst was used. e Five mol% of the catalyst was used. f One mol% of the catalyst was used.
CHCl3 afforded slightly better results in terms of enantioselectivity,
regardless of whether BINIM-2QN or BINIM-4Me-2QN were used
as ligands. Furthermore, in several cases (Entries 9, 12–16, and 18),
the inclusion of pentafluorophenol (PFP) as an additive in
combination with CHCl3 was found to improve enantioselectivities
of up to 91% ee. It is interesting to note that tandem Michael
addition product 4 was produced when the reaction was carried out
in the absence of additives or in the presence of i-PrOH (Entries 12
and 13). These results suggested that an appropriate protonating
agent such as HFIP or PFP is needed for the completion of the
reaction after the Michael addition. And the addition reaction is
probably in equilibrium with the reverse reaction before protona-
tion or tandem addition, in which a protonating agent influences the
enantioselectivity. The type of MS in the reaction did not show any
significant effects on the yield and enantioselectivity (Entries 18,
20, and 21); the absence of MS, however, resulted in unsatisfactory
yields and also in the hydrolysis of silyloxyfuran 1 to 2(5H)-
furanone (5) (Entry 19). The high enantioselectivity in the Ni(II)-
BINIM-catalyzed reaction with 3-acryloly-2-oxazolidinone (2a) is
noteworthy in comparison to the moderate enantioselectivity using
Cu(II)-bis(oxazoline) complex.4b
The optimized catalytic conditions were applied to the reactions
between various 2-silyloxyfurans and 3-alkenoyl-2-oxazolidinones
(Table 2). The BINIM-Ni(II)-catalyzed reaction of 1 with 3-croto-
noyl-2-oxazolidinone (2b) at 225 °C resulted in high anti-
selectivity; although the results were independent of the additives
and ligands (Entries 1–5), the use of HFIP as an additive in
combination with CHCl3 showed better results in terms of
enantioselectivity (Entries 2–5). In contrast, the use of PFP as an
additive required a longer reaction time to complete the reaction
with unsatisfactory results in terms of enantioselectivity (Entry 1).
Reactions of 1 with oxazolidinone 2c under similar conditions in
the presence of the catalyst (10 mol%) proceeded at a lower
temperature (240 °C) to give the corresponding Michael adducts
with high anti-selectivity ( > 99 : 1) and enantioselectivities
(88–93% ee) (Entries 6, 7, and 10). In this case, the use of PFP in
combination with CHCl3 afforded improved results in terms of
enantioselectivity. It is interesting to note that catalyst loading
could be decreased to 1 mol% without significant loss of diastereo-
and enantioselectivities (Entries 8 and 9).
reactions of 5-substituted-2-silyloxyfurans 8 and 10 with 3-alke-
noyl-2-oxazolidinones. Good enantioselectivities were obtained
with oxazolidinene 2a, whereas a slightly decreased enantiose-
lectivity was observed with oxazolidinoe 2c.
In summary, chiral Ni(II) complexes, which are readily prepared
from chiral BINIM-2QN or its derivatives and Ni(ClO4)2·6H2O,
were found to be efficient Lewis acids catalyst in the synthesis of
chiral g-butenolides via Michael addition reactions of 2-silylox-
yfurans with 3-alkenoyl-2-oxazolidinones resulting in high anti-
and enantioselectivities.
Notes and references
1 For examples, see: (a) Y. S. Rao, Chem. Rev., 1976, 78, 625; (b) E.
Fukusaki, S. Senda, Y. Nakazono and T. Omata, Tetrahedron, 1991, 47,
6223; (c) K. Mori, Tetrahedron, 1989, 45, 3233; (d) J. W. Wheeler, G. M.
Happ, J. Araujo and J. M. Pasteels, Tetrahedron Lett., 1972, 46, 4635; (e)
R. Bloch and L. Gilbert, J. Org. Chem., 1987, 52, 4603; (f) L. Thijs, W.
P. Waanders, E. H. M. Stokkingreef and B. Zwanenburg, Recl. Trav.
Chim. Pays-Bas, 1986, 105, 332.
2 S. P. Brown, N. C. Goodwin and D. W. C. MacMillan, J. Am. Chem. Soc.,
2003, 125, 1192.
3 (a) D. A. Evans, C. S. Burgey, M. C. Kozlowski and S. W. Tregay, J. Am.
Chem. Soc., 1999, 121, 686; (b) D. A. Evans, M. C. Kozlowski, J. A.
Murry, C. S. Burgey, K. R. Campos, B. T. Connell and R. J. Stapless, J.
Am. Chem. Soc., 1999, 121, 669; (c) M. Szosek, X. Franck, B. Figadère
and A. Cavé, J. Org. Chem., 1998, 63, 5169; (d) For reviews, see also: G.
Casiraghi, F. Zanardi, G. Appendino and G. Rassu, Chem. Rev., 2000,
100, 1929; (e) G. Casiraghi and G. Rassu, Synthesis, 1995, 607.
4 (a) H. Kitajima and T. Katsuki, Synlett, 1997, 568; (b) H. Kitajima, K. Ito
and T. Katsuki, Tetrahedron, 1997, 53, 17015; (c) G. Desimoni, G. Faita,
S. Filippone, M. Mella, M. G. Zampori and M. Zema, Tetrahedron, 2001,
57, 10203.
5 For reports of asymmetric Diels–Alder reactions between cyclopenta-
diene and 3-alkenoyl-2-oxazolidinones and asymmetric 1,3-dipolar
cycloaddition reactions between nitrones and 3-crotonoyl-2-oxazolidi-
none using the chiral BINIM-Ni(II) catalyst, see: (a) H. Suga, M. Mitsuda
and A. Kakehi, Chem. Lett., 2002, 900; (b) H. Suga, A. Kakehi, S. Ito and
H. Sugimoto, Bull. Chem. Soc. Jpn., 2003, 76, 327.
The reactions of 3-methyl-2-(trimethylsilyloxy)furan (6) with
oxazolidinones 2a–2c at 225 °C or 240 °C in the presence of the
chiral Ni(II) complexes (10 mol%) were carried out to afford the
corresponding products in high yields with extremely high
enantioselectivities (93–97% ee) (Entries 11–15). Furthermore,
high anti-selectivities for the reactions of 2b and 2c were observed.
The chiral Ni(II) catalysts were also applied to the Michael addition
6 For recent examples of asymmetric Mukaiyama Michael reactions using
HFIP as an additive, see: (a) D. A. Evans, M. C. Wills and J. N. Johnston,
Org. Lett., 1999, 1, 865; (b) D. A. Evans, K. A. Scheidt, J. N. Johston and
M. C. Wills, J. Am. Chem. Soc., 2001, 123, 4480.
C h e m . C o m m u n . , 2 0 0 4 , 1 4 1 4 – 1 4 1 5
1415