Synthesis of 1,1′-binaphthyl-2,2′-diyl phosphoroselenoic amides and their conversion to optically pure phosphoramidites

Article abstract of DOI:10.1246/cl.2006.1424

Optically pure phosphoroselenoyl chloride was reacted with racemic amines to give phosphoroselenoic amides as two diastereomeric mixtures in high yields. The diastereomeric mixtures were separated by fractional recrystallization or by chromatography. Extr

Full text of DOI:10.1246/cl.2006.1424

1424
Chemistry Letters Vol.35, No.12 (2006)
Synthesis of 1,10-Binaphthyl-2,20-diyl Phosphoroselenoic Amides
and Their Conversion to Optically Pure Phosphoramidites
Toshiaki Murai,ꢀ1 Shinsuke Inaji,1 Ken Morishita,1 Fumitoshi Shibahara,1 Makoto Tokunaga,2
Yasushi Obora,2 and Yasushi Tsuji2
1Department of Chemistry, Faculty of Engineering, Gifu University, Yanagido, Gifu 501-1193
2Catalysis Research Center and Division of Chemistry, Graduate School of Science, Hokkaido University, Sapporo 001-0021
(Received September 27, 2006; CL-061125; E-mail: mtoshi@gifu-u.ac.jp)
Table 1. Synthesis of phosphoroselenoic amides 3 by reacting 1 with
amines 2a
Optically pure phosphoroselenoyl chloride was reacted with
racemic amines to give phosphoroselenoic amides as two dia-
stereomeric mixtures in high yields. The diastereomeric mix-
tures were separated by fractional recrystallization or by chro-
matography. Extrusion of the selenium atom from the separated
amides led to diastereomerically pure phosphoramidites. The
ability of the obtained amidites to act as optically active ligands
was tested in the hydrogenation of an imine.
1
R
R
2
1
N
H
R
1
Se
P
Se
R
R
2
O
O
O
O
+
2
2
P
(Rax)-1
N
R
R
N
R
R
with or without
DMAP
Toluene, reflux
3
3'
b
Entry
Amine 2
Time/h
Yield/%
d
(Rax,S)-3b
(Rax,R)-3b'
35
2b
1-naphthyl
2
2
2
2
1
2
3
4
Phosphoramidites bearing a 1,10-bi-2-naphthoyl group have
been recognized as some of the most powerful ligands in catalyt-
ic asymmetric reactions1 since Feringa and co-workers reported
the first one bearing a N,N-dimethylamino group as a chiral dis-
criminating agent in 1994.2 Their synthesis generally involves
the reaction of chlorophosphites with amines.3 Alternatively,
the amino group substitution reaction of N,N-dimethylamino
phosphoramidites with other amines is used.4 However, only a
few phosphoramidites possessing a chiral center at the amino
group5 have been reported except for those with chiral 1-arylal-
kylamino groups.6
57
H N
2
e
2c
(Rax,S)-3c
(Rax,R)-3c'
46
49
H N
2
2d
2e
e
(Rax,S)-3d
(Rax,R)-3d'
44
H N
2
48
e
(Rax,S)-3e
(Rax,R)-3e'
36
HN
58
f,g
3f
3f'
3f + 3f'
34
44
18
5
34
25
We recently found that phosphoroselenoyl chloride 1 can be
obtained from PCl3, elemental selenium and 1,10-bi-2-naphthol
(Scheme 1).7 The chloride 1 is stable under neutral conditions
but reactive under basic conditions. We report here the reaction
of 1 with primary and secondary amines leading to phosphorose-
lenoic amides, separation of their diastereomers, and conversion
of the separated diastereomers to optically pure phosphorami-
dites.
2f
Ph
N
H
Ph
f
(Rax,S)-3g
(Rax,R)-3g'
3g + 3g'
30
22
36
c
6
2g
Ph
N
H
Ph
f,g
2h
OEt
3h
3h'
3h + 3h'
46
36
5
12
13
7
8
Ph
N
H
1) Et N 0 °C, 3 min
3
O
Se
P
2) (Rax)-1,1'-bi-2-naphthol
0 °C, 3 min
f,g
3i
3i'
3i + 3i'
41
40
14
O
O
O
O
O
O
=
PCl
3
Cl
N
2i
Ph
3) Se, Toluene reflux, 6 h
(Rax)-1 94%
Ph
N
H
Scheme 1.
The reaction of chloride 1 with racemic 1-phenylethylamine
(2a) proceeded smoothly under reflux in toluene (Scheme 2).8
Two diastereomers of phosphoroselenoic amide (Rax,S)-3a and
(Rax,R)-3a09,10 were obtained in a ratio of 39:61.11,15 These dia-
stereomers were separated by fractional crystallization to give
f
(Rax,S)-3j
(Rax,R)-3j'
3j + 3j'
14
c
2
9
OTBDMS
N
7
N
54
H
2j
f
(Rax,S)-3k
(Rax,R)-3k'
3k + 3k'
46
c
2.5
10
N
29
14
H
O
2k
Se
P
Se
P
O
O
aThe chloride 1 was reacted with amine 2 (2 equiv.) under reflux in
toluene unless otherwise noted. bIsolated yield. cAmine 2 (1.2 equiv.) and
DMAP (1.2 equiv.) was used. dDiastereomers were separated by fractional
recrystallization. eDiastereomers were separated by HPLC on silica gel.
fDiastereomers were separated by column chromatography on silica gel.
gThe absolute configuration of diastereomers is not determined.
O
O
+
+
1
H N
Ph
2
N
Ph
N
Ph
36%
Toluene
reflux
2 h
H
H
(2 equiv.)
(Rax,R)-3a'
60%
(Rax,S)-3a
2a
Scheme 2.
Copyright Ó 2006 The Chemical Society of Japan

Chemistry Letters Vol.35, No.12 (2006)
1425
1
1
Ph
Se
Ph
R
R
HN
Ph
N
n-Bu P
H (80 atm)
O
O
3
2
O
O
+
n-Bu P=Se
3
2
2
P
P
N
R
R
N
R
R
toluene
rt, 2 h
Ph
[Ir(cod)) ]BF (1.0 mol %)
*
2
4
3
4
5
100%
6
4 (1.5 mol %)
CH Cl
4g
4f'
4k
1% ee
OTBDMS
rt, 17 h
2
2
53% ee(R)-6
73% ee(S)-6
O
O
P
O
O
P
P
Ph
Ph
88%
N
N
N
*
O
O
Ph
Scheme 4.
Ph
4f' 92%
4g
4k 63%
new types of phosphoramidites, which are not readily accessible
by known synthetic procedures, but which may be important as
optically active ligands.
Scheme 3.
diastereomerically pure 3a and 3a0 in respective yields of 36 and
60%.
This work was supported in part by a Grant-in-Aid for Sci-
entific Research on Priority Area (No. 18037024, ‘‘Advanced
Molecular Transformations of Carbon Resources’’) from the
Ministry of Education, Culture, Sports, Science and Technology,
Japan. AIR WATER INC. kindly provided the optically active
1,10-bi-2-naphthol.
A wide variety of primary and secondary amines are
subjected to the amination reaction of 1. The results are shown
in Table 1. The reaction was carried out with either amines 2
(2 equiv.) (Entries 1–5, 7, and 8) or amines 2 (1.2 equiv.) in
the presence of 4-dimethylaminopyridine (DMAP, 1.2 equiv.)
(Entries 6, 9, and 10). In all cases, the substitution reaction of
1 with amines 2 took place selectively at the phosphorus atom
to give phosphoroselenoic amides 3 as a diastereomeric mixture
in high yields. The reaction rate depends on the substitution pat-
tern around the nitrogen atom of 2. The reaction with primary
amines 2b–2d was complete within 2 h (Entries 1–3), whereas
the reaction with acyclic secondary amines 2f–2i required a
longer reaction time (Entries 5–8). The diastereomers 3b and
3b0 were separated by fractional recrystallization. Other diaster-
eomers 3 were separated either by high performance recycle liq-
uid chromatography on silica gel or by column chromatography
on silica gel. The absolute configuration of the diastereomerical-
ly pure products 3 was determined by comparison to the
31P NMR spectra of authentic samples derived from optically
active amines. Alternatively, stereochemistry was deduced
based on X-ray molecular structure analyses of pure 3.12,15
Extrusion of the selenium atom of 3 was then performed
(Scheme 3). The reaction of 3 with Bu3P went to completion
within 2 h in toluene at room temperature to give the correspond-
ing phosphoramidites 4 along with Bu3P=Se. The complete
conversion of 3 to 4 was clearly confirmed by 31P NMR spectra,
but the phosphoramidites 4 (R = H) derived from primary
amines were not isolated, although their synthesis has already
been reported.13 Phosphoramidites 4 (R = H) are sensitive
toward air to give oxidized products along with several uniden-
tified products. In contrast, phosphoramidites 4 derived from
secondary amines were isolated in good yields, as exemplified
by 4f0, 4g, and 4k.
References and Notes
1
For recent examples: a) A. Zhang, T. V. RajanBabu, J. Am. Chem. Soc.
2006, 128, 5620. b) R. B. C. Jagt, P. Y. Toullec, D. Geerdink, J. G. De
Vries, B. L. Ferringa, A. J. Minnaard, Angew. Chem., Int. Ed. 2006, 45,
2789. c) M. T. Reetz, G. Mehler, O. Bondarev, Chem. Commun. 2006,
2292.
2
3
R. Hulst, N. K. de Vries, B. L. Feringa, Tetrahedron: Asymmetry
1994, 5, 699.
a) A. H. M. de Vries, A. Meetsma, B. L. Feringa, Angew. Chem., Int.
Ed. Engl. 1996, 35, 2374. b) L. A. Arnold, R. Imbos, A. Mandoli,
A. H. M. de Vries, R. Naasz, B. L. Feringa, Tetrahedron 2000, 56,
2865.
4
5
D. Pena, A. J. Minnaard, J. G. de Vries, B. L. Feringa, J. Am. Chem.
Soc. 2002, 124, 14552.
a) G. Francio, F. Faraone, W. Leitner, J. Am. Chem. Soc. 2002, 124,
736. b) R. Kumareswaran, M. Nandi, T. V. RajanBabu, Org. Lett.
2003, 5, 4345. c) T. Watanabe, T. F. Knoepfel, E. M. Carreira, Org.
Lett. 2003, 5, 4557. d) E. Cesarotti, S. Araneo, I. Rimoldi, S. Tassi,
J. Mol. Catal. A: Chem. 2003, 204–205, 211. e) A. Duursma, J.-G.
Boiteau, L. Lefort, J. A. F. Boogers, A. H. M. De Varies, J. G. De
Vries, A. J. Minnaard, B. L. Feringa, J. Org. Chem. 2004, 69, 8045.
For recent examples: a) Q.-H. Zeng, X.-P. Hu, Z.-C. Duan, X.-M.
6
Liang, Z. Zheng, J. Org. Chem. 2006, 71, 393. b) E. P. Kundig,
¨
P. D. Chaudhuri, D. House, G. Bernardinelli, Angew. Chem., Int. Ed.
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Biomol. Chem. 2006, 4, 1278. d) D. Polet, A. Alexakis, K. Tissot-
Croset, C. Corminboeuf, K. Ditrich, Chem. Eur. J. 2006, 12, 3596.
T. Murai, D. Matsuoka, K. Morishita, J. Am. Chem. Soc. 2006, 128,
4584.
A precedent for the reaction of achiral phosphoroselenoyl chlorides
with allylamine has been reported: Y. I. Mel’nik, D. I. Prots, Y. I.
Kolodii, Ukr. Khim. Zh. 1987, 53, 638.
7
8
9
The oxygen isologue of 3a was prepared at room temperature for 36 h
in a manner similar to that in Scheme 1: B.-Q. Gong, W.-Y. Chen,
B.-F. Hu, J. Org. Chem. 1991, 56, 423.
Finally, the ability of phosphoramidites 4 to act as optically
active ligands was tested in the Ir-catalyzed hydrogenation reac-
tion of imine 514 (Scheme 4). A catalytic amount of [Ir(cod)2]-
BF4 efficiently catalyzed the reaction, and the enantiomeric
excess was influenced by the substitution pattern in the phos-
phoramidites 4. The hydrogenation reaction of 5 in the presence
of 4g gave amine 6 in racemic form. The use of 4f0 effected the
asymmetric hydrogenation of 5 to give (R)-6 with 53% ee,
whereas the reaction in the presence of 4k led to (S)-6 with
73% ee.
10 The sulfur isologue of 3a was prepared by reacting phosphoramido-
thioic dichloride with 1,10-bi-2-naphthol: D. Fabbri, G. Delogu, O.
De Lucchi, J. Org. Chem. 1993, 58, 1748.
11 For spectroscopic properties of the new compounds, see the Supporting
Information.
12 For details of X-ray molecular structure analyses, see the Supporting
Information.
13 B. Bartels, C. Garcia-Yebra, G. Helmchen, Eur. J. Org. Chem. 2003,
1097.
14 For recent examples of the asymmetric catalytic hydrogenation of
imines: a) C. Moessner, C. Bolm, Angew. Chem., Int. Ed. 2005, 44,
7564. b) T. Imamoto, N. Iwadate, K. Yoshida, Org. Lett. 2006, 8, 2289.
15 Supporting Information is available electronically on the CSJ Journal
WEB site: http://www.csj.jp/journals/chem-lett/index.html.
In summary, we have demonstrated the highly efficient
synthesis of optically active phosphoroselenoic amides and their
purification in diastereomerically pure form. Extrusion of the
selenium atom of phosphoroselenoic amides with Bu3P provides
Published on the web (Advance View) November 18, 2006; doi:10.1246/cl.2006.1424