Copper-catalyzed asymmetric allylation of chiral N-tert-butanesulfinyl imines: Dual stereocontrol with nearly perfect diastereoselectivity

Article abstract of DOI:10.1039/c5ob00322a

Copper-catalyzed asymmetric allylation of chiral N-tert-butanesulfinyl imines has been described. Dual stereocontrol, through the combination of a chiral auxiliary and a chiral copper complex, has played an important role in achieving the nearly perfect d

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Copper-catalyzed asymmetric allylation of chiral N-
tert-butanesulfinyl imines: Dual stereocontrol with
nearly perfect diastereoselectivity
Cite this: DOI: 10.1039/x0xx00000x
YiꢀShuang Zhao,a,b Qiang Liu,b Ping Tian,*b JingꢀChao Tao*a and GuoꢀQiang Linb
Received 00th January 2015,
Accepted 00th January 2015
DOI: 10.1039/x0xx00000x
www.rsc.org/
found excellent applicability due to its feasibility of preparing
both enantiomers in large scale and readily removing the chiral
auxiliary under acidic conditions. In the last decade, Yus,8 our
group9 and other research groups10 established several efficient
methods using Znꢀ or Inꢀmediated asymmetric allylation of N-
tertꢀbutanesulfinyl imines to obtain enantioenriched homoalꢀ
lylic amines (Scheme 1a). In this case, the chiral imine subꢀ
strates determined the stereochemistry outcome. An alternative
powerful allylation was to react with achiral imines using chiral
ligandꢀmediated asymmetric transformation (Scheme 1b). Up to
now, Cu,11 Zn,12 In,13 Rh,14 and small organic molecules15 were
Copper-catalyzed asymmetric allylation of chiral N-tert
-
butanesulfinyl imines has been described. Dual stereocontrol,
through the combination of chiral auxiliary and chiral copper
complex, has played an important role in achieving the nearly
perfect diastereoselectivities (all d.r. > 99:1), especially for
ketimine substrates.
Chiral homoallylic amines not only serve as extremely significant
synthetic intermediates in organic synthesis, particularly for alkaloid
synthesis,1 but also exist in a wide range of naturallyꢀoccurring comꢀ
pounds and chiral drugs, for instance, (−)ꢀAlbine,2 ORG 34167,3 (−)ꢀ successfully applied in such enantioselective processes between
16
Histrionicotoxin 259A,4 NNZ 2591,5 (−)ꢀQuinolizidine 207I,6 and 3ꢀ
(2ꢀpropenyl)ꢀYohimbanꢀ17ꢀone7 (Fig. 1). Such importance has stimꢀ
ulated numerous research activities toward their enantioselective
synthesis. Among various methods, N-tertꢀbutylsulfinyl imines have
various imines and allylic boron compounds.
However,
homoallylic amines with extremely high optical purity (> 98%
ee) are generally rather difficult to achieve. To this end, the
dual stereocontrol process,17 through the combination of chiral
auxiliary and chiral copper complex, was developed and preꢀ
sented herein (Scheme 1c). Nearly perfect diastereoselectivities
(all d.r. > 99:1) were successfully reached, especially for
ketimine substrates.
Fig. 1 Chiralꢀhomoallylicꢀamineꢀcontaining natural products and drugs
aCollege of Chemistry and Molecular Engineering, Zhengzhou University, 75
Daxue Road, Zhengzhou, Henan 450052, China. Tel.: +86-371-67767200
E-mail: jctao@zzu.edu.cn.
bCAS Key Laboratory of Synthetic Chemistry of Natural Substances, Shang-
hai Institute of Organic Chemistry, Chinese Academy of Sciences, 345 Ling-
ling Road, Shanghai 200032, China. Tel.: +86-21-54925081
E-mail: tianping@sioc.ac.cn.
Scheme 1 Dual stereocontrol in Cuꢀcatalyzed asymmetric allylation
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With this challenge in mind, a set of representative phosꢀ
With the optimal reaction conditions identified, various N-
phorus ligands were evaluated for Cuꢀcatalyzed asymmetric tertꢀbutanesulfinyl aldimines were investigated, and the results
allylation of chiral N-tertꢀbutanesulfinyl aldimine 1a, and the are summarized in Table 2. All substituted phenyl aldimine
results are summarized in Table 1. Initially, poor diastereoseꢀ substrates, regardless of the electronꢀdonating or electronꢀ
lectivity (d.r. = 1.9:1) was obtained when no ligand was applied withdrawing property of the substituent at the phenyl ring, afꢀ
in this reaction (Table 1, entry 1). Using the simple triꢀ forded the corresponding chiral homoallylic amine products in
phenylphosphine (L1) as ligand, the d.r. value was greatly inꢀ
creased to 19:1 (Table 1, entry 2). Three bisphosphine ligands,
excellent yields (90
ties (all d.r. > 99:1, Table 2, entries 1
dimine substrates, the allylation reaction also proceeded
smoothly and the reaction yields and diastereoselectivities still
maintained at an excellent level (Table 2, entries 11−13).
−
99%) and nearly perfect diastereoselectiviꢀ
−
10). As for the alkyl alꢀ
L2
desired product was observed, along with only partial decomꢀ
position of starting material (Table 1, entries 3 5). Thus we
turned our attention back to monophosphine ligand. The d.r.
value was further raised to 35:1 with ( )ꢀMonoPhos (L5) as
ligand (Table 1, entry 6). To our delight, bulky phosphoꢀ Table 2 Substrate scope of various aldimines.a
ramidite ligand (
)ꢀL618 could dramatically improve the reacꢀ
−L4, were subsequently investigated, however almost no
−
R
S
tion yield and diastereoselectivity up to 80% and >99:1 d.r.
value, respectively (Table 1, entry 7). Utilizing racemic L6 as
ligand had little impact on the outstanding diastereoselectivity
(99:1 d.r.) and only the yield decreased to 65% (Table 1, entry
8), which revealed that the chiral bulky phosphoramidite ligand
L6 only acted as a large coordination group. Increasing the
Entry
1
2
3
4
5
6
7
8
1
1a
1b
1c
1d
1e
1f
1g
1h
1i
R
C6H5
t (h)
40
40
40
40
40
40
40
40
40
40
10
20
40
3
3a
3b
3c
3d
3e
3f
3g
3h
3i
Yield (%)b
d.r.c
97
99
93
99
98
99
92
90
91
94
99
90
91
>99:1
>99:1
>99:1
>99:1
>99:1
>99:1
>99:1
>99:1
>99:1
>99:1
>99:1d
>99:1
>99:1d
allylboronic acid pinacol ester (
in considerable improvement of yield (Table 1, entry 9). Using
)ꢀL6 as ligand, the nearly perfect diastereoselectivity had no
2) loading to 2.0 equiv resulted
4ꢀMeꢀC6H4
4ꢀClꢀC6H4
4ꢀCF3ꢀC6H4
4ꢀMeOꢀC6H4
3ꢀMeꢀC6H4
3ꢀClꢀC6H4
2ꢀMeꢀC6H4
2ꢀClꢀC6H4
βꢀnaphthyl
ethyl
(
R
change and only the yield reduced slightly to 89% (Table 1,
entry 10).
Table 1 Initial evaluation of various ligandsa
9
10
11
12
13
1j
3j
1k
1m
1n
3k
3m
3n
isopropyl
phenethyl
aThe reaction was carried out with
1
(0.2 mmol), allylboronic acid pinaꢀ
, 0.4 mmol, 2.0 equiv), CuCl (5 mol%), ( )ꢀL6 (6 mol%),
Bu (6 mol%) and anhydrous MeOH (32 L, 4.0 equiv) in THF
(2.0 mL) at room temperature under Ar atmosphere. Yield of the isoꢀ
lated product. cd.r. = (RS , Determined by 1H NMR analyꢀ
)ꢀ : (RS )ꢀ
sis. dd.r. = (RS
)ꢀ : (RS )ꢀ
col ester (
2
S
NaO
t
ꢀ
b
,R
3
,S 3
,S
3
,R 3.
The absolute configuration and d.r. values of homoallylic
1
amines
3 were determined on the basis of their H NMR analyꢀ
sis and chemical correlation with the known compounds.9 The
nearly perfect d.r. value of 3a was further confirmed by the
HPLC analysis of its acetyl derivative 4a 19
, which ensured the
accuracy of 1H NMR analysis (Scheme 2).
Entry
L
Conversion (%)b
Yield (%)c
45
49
1.2
trace
trace
68
d.r.d
1.9:1
19:1
2.6:1
−
1
2
3
4
5
6
7
8
9e
48
61
24
25
23
83
81
71
100
−
L1 (PPh3)
L2
L3
L4
L5
(S)ꢀL6
racꢀL6
(S)ꢀL6
−
35:1
>99:1
99:1
>99:1
80
65
93
89
10e
(R)ꢀL6
100
>99:1
aThe reaction was carried out with 1a (0.2 mmol), allylboronic acid
Scheme 2 Determining the absolute configuration and d.r. value of 3a.
pinacol ester (2, 0.3 mmol, 1.5 equiv), CuCl (5 mol%), chiral ligand
(
L
*, 6 mol%), NaO
t
Bu (6 mol%) and anhydrous MeOH (32 L, 4.0
ꢀ
equiv) in THF (2.0 mL) at room temperature under Ar atmosphere.
Given the highly diastereoselective nature of this allylation
reaction, ketimine substrates were also examined. At the outset,
bBased on the isolated and recovered 1a. cYield of the isolated product.
dd.r. = (RS
,R)ꢀ3a: (RS
,S
)ꢀ3a, Determined by H NMR analysis. e2 (2.0
1
(
RS)ꢀ5a was subjected to this reaction, only 11.8:1 d.r. value
was observed, which probably suggested that the chiral ligand
)ꢀL6 mismatched the enantioenriched substrate (RS)ꢀ5a
equiv) was used. Bpin = (pinacolato)boron.
(
S
(Scheme 3). To verify this hypothesis, (SS)ꢀ5a was used in this
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reaction. As we expected, > 99:1 d.r. value was achieved,
With the known matching pattern of the enantioenriched
which clearly suggested that the chiral ligand ( )ꢀL6 matched imine substrate and chiral ligand, various N-tertꢀbutanesulfinyl
S
the enantioenriched substrate (SS)ꢀ5a. The dual stereocontrol, ketimines were subsequently tested, and the results are summaꢀ
with the combination of chiral auxiliary and chiral copper comꢀ rized in Table 3. With a substituent, regardless of its electronꢀ
plex, pushed the diastereoselectivity to a nearly perfect level. It donating or electronꢀwithdrawing property, at the phenyl ring,
should be noted that 5 equivalent of allylboronic acid pinacol the reaction could readily provide the corresponding quaternary
ester (2) must be used to ensure the full conversion of 5a. The
allylic amine (Table 3, entries 1−10). It is worth mentioning
absolute configuration and d.r. values of quaternary homoalꢀ
that excellent yield and d.r. value were both achieved for the
sterically hindered 2ꢀsubstituted phenyl substrate 5d (Table 3,
entry 4).
1
lylic amine 6a were determined on the basis of their H NMR
analysis and chemical correlation with the known compounds,
and further confirmed by HPLC analysis of its acetyl derivative
The different stereocontrol outcome between aldimine and
ketimine might be mainly attributed to their conformation difꢀ
ference. In N-tertꢀbutanesulfinyl aldimine 1c, the C=N bond is
pseudoꢀcis to the S=O bond, whereas a pseudoꢀtrans conforꢀ
7a 20
.
mation is observed in ketimine 5f 9a
. The common Zimmermanꢀ
CuCl (5 mol%)
(S)-L6 (6 mol%)
Traxler chairꢀlike transition states should be firstly excluded
from the attack pathway because of the steric congestion imꢀ
posed by the bulky ligand (S)ꢀL6 bonding to copper. Due to the
steric hindrance induced by tertiary butyl group and its inherent
pseudoꢀcis conformation between C=N bond and S=O bond,
allylcopper attacked the less hindered reꢀface of aldimine (RS)ꢀ
Bpin
(5.0 equiv)
2
S
S
S
+
+
N
O
HN
O
HN
O
t-BuONa (6 mol%)
MeOH ( 4 equiv)
THF, RT, 40 h
Me
Ph
Me
Ph
S
R
Ph
Me
5a (RS)
6a (RS,S)
6a (RS,R)
80% yield
d.r. [(RS,S):(RS,R)] = 11.8:1
Determined by 1H NMR analysis
(1) HCl, MeOH, RT
(2) Ac2O, Et3N, DCM, RT
quant.
1a to offer (
trast, the allylic addition took place at the reꢀface of ketimine
SS)ꢀ5a to afford ( )ꢀhomoallylic amine 7a, owing to its intrinꢀ
R)ꢀhomoallylic amine 3a (Scheme 4, TS I). In conꢀ
24
NHAc
Found: [
(R)-7a, Lit.: [
]
= 31.0 (c = 0.5, CHCl3)
Me
Ph
D
(
R
]
22 = +65.4 (c = 1.2, CHCl3)[20]
S
D
sic pseudoꢀtrans conformation between C=N bond and S=O
bond (Scheme 4, TS II).
7a (S)
Determined by HPLC
84.1% ee
CuCl (5 mol%)
(S)-L6 (6 mol%)
Bpin
(5.0 equiv)
2
S
N
S
S
+
+
O
HN
O
HN
Me
O
t-BuONa (6 mol%)
MeOH ( 4 equiv)
THF, RT, 40 h
Me
Ph
R
S
Ph
Me
Ph
5a (SS)
6a (SS,R)
91% yield
d.r. [(SS,R):(SS,S)] = >99:1
6a (SS,S)
Determined by 1H NMR analysis
(1) HCl, MeOH, RT
(2) Ac2O, Et3N, DCM, RT
quant.
NHAc
Found: [
(R)-7a, Lit.: [
]
24 = +39.5 (c = 0.5, CHCl3)
D
Me
Ph
]
22 = +65.4 (c = 1.2, CHCl3)[20]
R
D
7a (R)
98.9% ee
Determined by HPLC
Scheme 3 Investigation of matching/mismatching ketimine substrate.
Table 3 Substrate scope of various ketimines.a
Scheme 4 Mechanistic proposals relating to the allylation stereocontrol.
Conclusions
Entry
1
2
3
4
5
6
7
8
5
Ar
C6H5
t (h)
40
70
70
70
70
70
70
70
70
70
6
Yield (%)b
d.r.c
In summary, copperꢀcatalyzed asymmetric allylation of chiral
Nꢀtertꢀbutanesulfinyl imines, including aldimines and
ketimines, has been successfully established. This reaction proꢀ
ceeded smoothly at room temperature, affording optically acꢀ
tive homoallylic amines with excellent yields (90−99%) and
diastereoselectivities (all d.r. > 99:1). Notably, ketimine subꢀ
strates, through the matched dual stereocontrol from chiral auxꢀ
iliary and chiral copper complex, could also provide nearly
perfect diastereoselectivity. Further studies on the applications
of homoallylic amines are in progress in our laboratories.
5a
5b
5c
5d
5e
5f
5g
5h
5i
6a
6b
6c
6d
6e
6f
6g
6h
6i
91
93
93
91
92
92
91
93
90
91
>99:1
>99:1
>99:1
>99:1
>99:1
>99:1
>99:1
>99:1
>99:1
>99:1
4ꢀMeꢀC6H4
3ꢀMeꢀC6H4
2ꢀBrꢀC6H4
4ꢀFꢀC6H4
4ꢀClꢀC6H4
4ꢀBrꢀC6H4
4ꢀMeOꢀC6H4
4ꢀCF3ꢀC6H4
3ꢀClꢀC6H4
9
10
5j
6j
aThe reaction was carried out with
4
(0.2 mmol), allylboronic acid pinaꢀ
, 1.0 mmol, 5.0 equiv), CuCl (5 mol%), ( )ꢀL6 (6 mol%),
Bu (6 mol%) and anhydrous MeOH (32 L, 4.0 equiv) in THF (2.0
col ester (
2
S
NaO
t
ꢀ
Acknowledgments
b
mL) at room temperature under Ar atmosphere. Yield of the isolated
product. cDetermined by 1H NMR analysis.
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Financial support for this work was generously provided by the
973 Program (2015CB856600), the National Natural Science
Foundation of China (NSFC 21372243, 21232009, 21102161),
the Shanghai Municipal Committee of Science and Technology
(13JC1406900), the Collaborative Innovation Center of Chemiꢀ
cal Science and Engineering (Tianjin), and the State Key Laꢀ
boratory of Bioorganic and Natural Products Chemistry
(SIOC). We thank Dr. Hanqing Dong (Arvinas Inc.) for helpful
discussion.
11 (a) R. Wada, T. Shibuguchi, S. Makino, K. Oisaki, M. Kanai and M.
Shibasaki, J. Am. Chem. Soc., 2006, 128, 7687; (b) E. M. Vieira, M.
L. Snapper and A. H. Hoveyda, J. Am. Chem. Soc., 2011, 133, 3332.
12 M. Fujita, T. Nagano, U. Schneider, T. Hamada, C. Ogawa and S.
Kobayashi, J. Am. Chem. Soc., 2008, 130, 2914.
13 A. Chakrabarti, H. Konishi, M. Yamaguchi, U. Schneider and S.
Kobayashi, Angew. Chem. Int. Ed., 2010, 49, 1838.
14 (a) Y. Luo, H. B. Hepburn, N. Chotsaeng and H. W. Lam, Angew.
Chem. Int. Ed., 2012, 51, 8309; (b) H. B. Hepburn and H. W. Lam,
Angew. Chem. Int. Ed., 2014, 53, 11605.
Notes and references
15 (a) D. L. Silverio, S. Torker, T. Pilyugina, E. M.Vieira, M. L. Snapꢀ
per, F. Haeffner and A. H. Hoveyda, Nature, 2013, 494, 216; (b) S.
1
For recent reviews, see: (a) T. R. Ramadhar and R. A. Batey, Synthe-
sis, 2011, 1321; (b) G.ꢀQ. Lin, M.ꢀH. Xu, Y.ꢀW. Zhong and X.ꢀW.
Sun, Acc. Chem. Res., 2008, 41, 831; (c) P. V. Ramachandran and T.
E. Burghardt, Pure Appl. Chem., 2006, 78, 1397; (d) C. O. Puentes
and V. Kouznetsov, J. Heterocyclic Chem., 2002, 39, 595.
Lou, P. N. Moquist and S. E. Schaus, J. Am. Chem. Soc., 2007, 129
,
15398.
16 For recent reviews, see: H.ꢀX. Huo, J. R. Duvall, M.ꢀY. Huang and R.
Hong, Org. Chem. Front., 2014,
Chem., 2008, 80, 913.
1, 303; (b) D. G. Hall, Pure Appl.
2
(a) W. Wysocka and T. Brukwicki, Tetrahedron, 2003, 59, 8597; (b)
17 Selected examples: (a) R. Doran, M. P. Carroll, R. Akula, B. F. Hoꢀ
gan, M. Martins, S. Fanning and P. J. Guiry, Chem. Eur. J., 2014,
T. Schmeller, M. Sauerwein, F. Sporer and M. Wink, J. Nat. Prod.
,
−
1994, 57, 1316; (c) M. Wink, C. Mei
try, 1995, 38, 139.
βner and L. Witte, Phytochemis-
20, 15354; (b) M. Vlatković, L. Bernardi, E. Otten and B. L. Feringa,
Chem. Commun., 2014, 50, 7773; (c) Z. Liu and M. Shi, Tetrahe-
dron: Asymmetry, 2009, 20, 119.
3
4
5
J. Kelder, P. D. J. Grootenhuis, D. M. Bayada, L. P. C. Delbressine
and J.ꢀP. Ploemen, Pharm. Res., 1999, 16, 1514.
18 C. Defieber, M. A. Ariger, P. Moriel and E. M. Carreira, Angew.
Chem. Int. Ed., 2007, 46, 3139.
(a) C. J. Smith, A. B. Holmes and N. J. Press, Chem. Commun., 2002,
1214; (b) J. W. Daly and T. F. Spande, J. Nat. Prod., 1986, 49, 265.
(a) J. Guan, R. Zhang, L. DaleꢀGandar, S. Hodgkinson and M. H.
Vickers, Behav. Brain Res., 2010, 210, 221; (b) J. Guan, S. Mathai,
P. Harris, J.ꢀY. Wen, R. Zhang, M. Brimble and P. Gluckman, Neu-
ropharmacology, 2007, 53, 749.
19 (a) A. Hietanen, T. Saloranta, S. Rosenberg, E. Laitinen, R. Leino
and L. T. Kanerva, Eur. J. Org. Chem., 2010, 909; (b) T. Kohara, Y.
Hashimoto and K. Saigo, Tetrahedron, 1999, 55, 6453.
20 D. H. Hua, S. W. Miao, J. S. Chen and S. Iguchi, J. Org. Chem.
1991, 56, 4.
,
6
(a) N. Toyooka and H. Nemoto, Tetrahedron Lett., 2003, 44, 569; (b)
P. Jain, H. M. Garraffo, H. J. C. Yeh, T. F. Spande and J. W. Daly, J.
Nat. Prod., 1996, 59, 1174.
7
8
P. C. Unangst, L. D. Bratton, D. T. Connor, B. D. Roth, J. R. Rubin
and B. K. Trivedi, J. Heterocyclic Chem., 2000, 37, 1081.
Selected examples: (a) J. A. Sirvent, F. Foubelo and M. Yus, Eur. J.
Org. Chem., 2013, 2461; (b) J. A. Sirvent, F. Foubelo and M. Yus,
Chem. Commun., 2012, 48, 2543; (c) J. C. GonzálezꢀGómez, M. Meꢀ
djahdi, F. Foubelo and M. Yus, J. Org. Chem., 2010, 75, 6308; (d) F.
Foubelo and M. Yus, Tetrahedron: Asymmetry, 2004, 15, 3823.
Selected examples: (a) T. Guo, R. Song, B.ꢀH. Yuan, X.ꢀY. Chen, X.ꢀ
W. Sun and G.ꢀQ. Lin, Chem. Commun., 2013, 49, 5402; (b) A. Shen,
Z.ꢀT. He, H.ꢀJ. Yu, Y. Fukui, P. Tian and G.ꢀQ. Lin, Synlett, 2013,
1649; (c) A. Shen, M. Liu,Z.ꢀS. Jia, M.ꢀH. Xu and G.ꢀQ. Lin, Org.
Lett., 2010, 12, 5154; (d) M. Liu, A. Shen, X.ꢀW. Sun, F. Deng, M.ꢀ
H. Xu and G.ꢀQ. Lin, Chem. Commun., 2010, 46, 8460; (e) M. Liu,
9
X.ꢀW. Sun, M.ꢀH. Xu and G.ꢀQ. Lin, Chem.
−
Eur. J., 2009, 15
,
,
,
10217; (f) X.ꢀW. Sun, M. Liu, M.ꢀH. Xu and G.ꢀQ. Lin, Org. Lett.
2008, 10, 1259; (g) X.ꢀW. Sun, M.ꢀH. Xu and G.ꢀQ. Lin, Org. Lett.
2006, 8, 4979.
10 Selected examples: (a) G. Lemonnier, N. Van Hijfte, T. Poisson, S.
CouveꢀBonnaire and X. Pannecoucke, J. Org. Chem. 2014, 79, 2916;
(b) S. Fustero, R. Lázaro, L. Herrera, E. Rodríguez, N. Mateu and P.
Barrio, Org. Lett., 2013, 15, 3770; (c) D. Chen and M.ꢀH. Xu, Chem.
Commun., 2013, 49, 1327; (d) M. L. Schulte and C. W. Lindsley,
Org. Lett., 2011, 13, 5684; (e) L. R. Reddy, B. Hu, M. Prashad and
K. Prasad, Org. Lett., 2008, 10, 3109.
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