Z-selective horner-wadsworth-emmons-type reaction using a 10-P-5 phosphorane bearing bidentates derived from 1-naphthol

Article abstract of DOI:10.1246/cl.2010.1138

A Horner-Wadsworth-Emmons-type 10-P-5 phosphorane reagent bearing bidentate ligands from 1-naphthol was prepared and examined in the olefination of aldehydes. Z-Selectivity was generally high except for the case of 3-phenylpropanal, and acetophenone was a

Full text of DOI:10.1246/cl.2010.1138

doi:10.1246/cl.2010.1138
1138
Published on the web September 28, 2010
Z-Selective Horner-Wadsworth-Emmons-type Reaction
Using a 10-P-5 Phosphorane Bearing Bidentates Derived from 1-Naphthol
Satoshi Kojima,*1,2 Jun-ya Arimura,1 and Kazumasa Kajiyama3
1Department of Chemistry, Graduate School of Science, Hiroshima University,
1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526
2Center for Quantum Life Sciences, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526
3Department of Chemistry, School of Science, Kitasato University, 1-15-1 Kitasato, Sagamihara, Kanagawa 228-8555
(Received August 13, 2010; CL-100701; E-mail: skojima@sci.hiroshima-u.ac.jp)
A Horner-Wadsworth-Emmons-type 10-P-5 phosphorane
Preparation of the 10-P-5 HWE reagent 4 was carried out by
reacting the known P-H phosphorane 38 with ClCH2CO2Et in
the presence of DBU. The spectroscopic data of 4 was in accord
with expectations for a 10-P-5 compound.9
reagent bearing bidentate ligands from 1-naphthol was prepared
and examined in the olefination of aldehydes. Z-Selectivity was
generally high except for the case of 3-phenylpropanal, and
acetophenone was also found to react with relatively high
selectivity.
O
P
O
P
ClCH2CO2Et, DBU
H
ð1Þ
CH2CO2Et
THF, 0 °C, 3 h
The Wittig reaction and its phosphoryl variant, the Horner-
Wadsworth-Emmons (HWE) reaction are valuable methods for
introducing double bonds with carbon-carbon bond formation.1
For disubstituted alkenes conjugated with an electron-with-
drawing group such as a carbonyl or a cyano group, in order to
prepare the thermodynamically less stable Z-olefin with high
selectivity, the Still reagent2 and the Ando reagent3 have
emerged as highly versatile reagents. Useful variants4 based
upon the Ando reagent along with highly selective Peterson-type
reagents5 have also been disclosed. We6 and Evans7 have
independently found that 10-P-5 phosphoranes 1 and 2,
respectively, could also function as HWE reagents, although
they are already pentacoordinated (Figure 1). This is interesting
in light of the fact that in the ordinary HWE reaction the
tetracoordinated reagent has to increase its valency to a
pentacoordinated state in order to yield the olefinic product.
With our system, which utilizes the Martin ligand, it was also
found that olefins could be obtained with almost exclusive Z-
selectivity when the reagent bore an ester6a or an amide
moiety,6b and moderate selectivity was observed when it had a
cyano group.6b Although the reagents showed high selectivity, a
drawback was that the reactivity of the reagents was rather low
and the reaction temperature could not be lowered below 0 °C
for ester and amide systems. We attributed this low reactivity to
the presence of the bulky trifluoromethyl groups in the bidentate
Martin ligand. Thus, to increase reactivity we decided to
examine a 10-P-5 phosphorane reagent bearing a flat bidentate
generated from 1-naphthol, of which the parent 3 has found
utility in the preparation of unique transition-metal complexes.8
O
O
82%
3
4
The reaction of 4 with n-BuLi at 0 °C followed by
benzaldehyde proceeded to give an olefinic product with 93:7
selectivity in favor of the Z-olefin (Table 1). This reaction was
found to proceed even at ¹78 °C with an increased selectivity of
98:2, although more sluggishly, as the reaction was not complete
after 3 h at this temperature. Nonetheless, it was evident that the
reaction proceeded faster than that of phosphorane 1. With
phosphorane 1, a counter cation effect was observed, and
selectivity was in the order of K+ > Na+ > Li+. Thus, we next
examined the reaction of benzaldehyde using t-BuOK and NaH
as bases. The reaction using t-BuOK turned out to be somewhat
messy, and thus NaH was the optimum base among the three
examined, giving the product with selectivity up to 96:4 at
0 °C.10
Table 1. Reactions of 4 with various aldehydes
Entry RCHO
Base
n-BuLi ¹78 °C, 3 h
n-BuLi ¹78 to 0 °C, 3 h 97:3
Conditionsa
Z:E Yield/%
1
2
3
4
5
6
7
8
9
PhCHO (5a)
98:2
53
73
73
83
61
66
64
70
68
58
89
n-BuLi 0 °C, 3 h
NaH 0 °C, 3 h
t-BuOK 0 °C, 3 h
93:7
96:4
95:5
97:3
99:1
95:5
97:3
96:4
97:3
o-MeOC6H4CHO (5b) NaH
0 °C, 3 h
¹40 °C, 6 h
0 °C, 3 h
¹40 °C, 6 h
0 °C, 3 h
¹40 °C, 6 h
0 °C, 3 h
NaH
m-MeOC6H4CHO (5c) NaH
NaH
O
F3C CF3
O
O
P
10 p-MeOC6H4CHO (5d) NaH
11 NaH
12 PhCH2CH2CHO (5e) NaH
O
CH2CO2Me
P
CH2X
O
O
O
85:15 70
86:14 75
13
NaH
NaH
NaH
NaH
¹78 °C, 12 h
0 °C, 3 h
F3C CF3
O
14 PhMeCHCHO (5f)
15
16 PhMe2CCHO (5g)
97:3
99:1
99:1
68
70
72
X = CO2R, CONR2, CN
¹78 °C, 12 h
0 °C, 6 h
1
2
aAll reactions were carried out in THF.
Figure 1.
Chem. Lett. 2010, 39, 1138-1139
© 2010 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/

1139
Phosphorus Ylides, Wiley-VCH, Weinheim, 1999. j) K.
Ando, J. Synth. Org. Chem., Jpn. 2000, 58, 869. k) M.
Edmonds, A. Abell, in Modern Carbonyl Olefination, ed. by
T. Takeda, Wiley-VCH, Weinheim, 2004, pp. 1-17. l) F.
López-Ortiz, J. G. López, R. A. Manzaneda, I. J. P. Álvarez,
Mini-Rev. Org. Chem. 2004, 1, 65.
W. C. Still, C. Gennari, Tetrahedron Lett. 1983, 24, 4405.
a) K. Ando, Tetrahedron Lett. 1995, 36, 4105. b) K. Ando,
J. Org. Chem. 1997, 62, 1934. c) K. Ando, J. Org. Chem.
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K. Kokin, J. Motoyoshiya, S. Hayashi, H. Aoyama, Synth.
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H. Ohno, T. Ibuka, J. Org. Chem. 2000, 65, 4745.
R
R
1) base
ð2Þ
4
2) RCHO (5)
CO2Et
CO2Et
6-E
6-Z
2
3
To determine the scope of the reaction, o-, m- and p-MeO-
substituted benzaldehydes were reacted similarly with NaH as
the base at 0 °C, and it was found that high Z-selectivity could be
attained regardless of the position of the substituent. Carrying
out the reaction at ¹40 °C led to a slight increase in selectivity
for all three substrates. Noteworthy is that nearly complete
control could be observed for the most sterically hindered o-
substituted substrate. As for aliphatic aldehydes, 3-phenylpro-
panal, 2-phenylpropanal, and 2-methyl-2-phenylpropanal were
examined. High selectivity was observed for the two ¡-branched
aldehydes, whereas selectivity was moderate for unbranched 3-
phenylpropanal. Lowering the temperature led to nearly com-
plete control for 2-phenylpropanal. However, practically no
improvement was observed for 3-phenylpropanal.
In addition to the fact that the reactions could be carried out
at ¹78 °C, the increased reactivity of phosphorane 4 compared
with 1 could be demonstrated by the reaction with acetophenone.
Thus, the reaction proceeded at 0 °C to give the olefinic product
with the relatively high selectivity of 91:9, in favor of the Z-
product. The reaction required less time when it was carried out
at rt, albeit with somewhat lower selectivity. Unfortunately,
bulkier ketones such as alkyl phenyl ketones with higher alkyl
groups were reluctant to react.
4
5
a) F. P. Touchard, N. Capelle, M. Mercier, Adv. Synth. Catal.
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1790.
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2000, 1795. b) S. Kojima, H. Inai, T. Hidaka, T. Fukuzaki, K.
Ohkata, J. Org. Chem. 2002, 67, 4093. c) S. Kojima, T.
Fukuzaki, A. Yamakawa, Y. Murai, Org. Lett. 2004, 6, 3917.
a) S. Kojima, R. Takagi, K.-y. Akiba, J. Am. Chem. Soc. 1997,
119, 5970. b) S. Kojima, K. Kawaguchi, S. Matsukawa, K.
Uchida, K.-y. Akiba, Chem. Lett. 2002, 170. For related
mechanistic studies see: c) S. Kojima, K.-y. Akiba, Tetra-
hedron Lett. 1997, 38, 547. d) S. Kojima, K. Kawaguchi, K.-y.
Akiba, Tetrahedron Lett. 1997, 38, 7753. e) S. Matsukawa, S.
Kojima, K. Kajiyama, Y. Yamamoto, K.-y. Akiba, S. Re, S.
Nagase, J. Am. Chem. Soc. 2002, 124, 13154. f) S. Kojima, K.
Kawaguchi, S. Matsukawa, K.-y. Akiba, Tetrahedron 2003,
59, 255.
6
7
8
M. L. Bojin, S. Barkallah, S. A. Evans, Jr., J. Am. Chem. Soc.
1996, 118, 1549.
a) K. Kajiyama, Y. Hirai, T. Otsuka, H. Yuge, T. K.
Miyamoto, Chem. Lett. 2000, 784. b) K. Kajiyama, H.
Yuge, T. K. Miyamoto, Phosphorus, Sulfur Silicon Relat.
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Miyazawa, T. K. Miyamoto, Chem. Lett. 2003, 32, 332. d) K.
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Miyamoto, Eur. J. Inorg. Chem. 2009, 5516.
Me
Ph
Ph
Me
1) NaH
ð3Þ
4
2) acetophenone
CO2Et
CO2Et
7-E
7-Z
4: Mp 117 °C; 1H NMR (500 MHz, CDCl3): ¤ 8.30 (dd,
J = 12.2, 7.0 Hz, 2H), 7.99 (dd, J = 7.9, 2.7 Hz, 2H), 7.62
(dd, J = 13.7, 6.7 Hz, 2H), 7.47 (dd, J = 8.2, 7.6 Hz, 2H),
7.33 (dd, J = 8.2, 2.2 Hz, 2H), 6.90 (d, J = 7.6 Hz, 2H), 3.92
(dq, J = 10.4, 6.7 Hz, 1H), 3.80 (dq, J = 10.4, 6.7 Hz, 1H),
3.76 (dd, J = 22.7, 14.3 Hz, 1H), 3.72 (dd, J = 22.2, 14.3 Hz,
1H), 0.74 (t, J = 7.3 Hz, 3H); 13C NMR (125 MHz, CDCl3): ¤
166.6 (J = 7 Hz), 155.9 (J = 2 Hz), 134.3 (J = 8 Hz), 131.9
(J = 14 Hz), 131.4 (J = 4 Hz), 129.3 (J = 26 Hz), 129.1,
128.2 (J = 17 Hz), 124.4 (J = 161 Hz), 116.1, 104.0 (J = 2
Hz), 61.0, 43.4 (J = 117 Hz), 13.4; 31P NMR (202 MHz,
CDCl3): ¤ ¹37.5; HRMS(EI+) m/z: calcd for C24H19O4P
402.1021, found 402.1001.
rt, 24 h
0 °C, 48 h
87 : 13
91 : 9
76%
80%
9
In conclusion, we have found that the novel 10-P-5
phosphorane HWE reagent 4 could be utilized as an efficient
reagent for the preparation of Z-olefins from aldehydes and that
acetophenone also reacts with relatively high selectivity. These
results provide valuable insight for the designing of other 10-P-5
type HWE reagents that might be of higher utility.
References and Notes
1
For leading reviews see: a) W. S. Wadsworth, Jr., in Organic
Reactions, ed. by W. G. Dauben, John Wiley & Sons, New
York, 1977, Vol. 25, pp. 73-253. b) J. I. G. Cadogan,
Organophosphorus Reagents in Organic Synthesis, Academic
Press, New York, 1979. c) B. E. Maryanoff, A. B. Reitz,
Chem. Rev. 1989, 89, 863. d) S. E. Kelly, in Comprehensive
Organic Synthesis, ed. by B. M. Trost, I. Fleming, Pergamon
Press, Oxford, 1991, Vol. 1, pp. 730-817. e) A. W. Johnson,
Ylides and Imines of Phosphorus, Wiley-Interscience, New
York, 1993. f) E. Vedejs, M. J. Peterson, Top. Stereochem.
1994, 21, 1. g) E. Vedejs, M. J. Peterson, Adv. Carbanion
Chem. 1996, 2, 1. h) J. Clayden, S. Warren, Angew. Chem.,
Int. Ed. Engl. 1996, 35, 241. i) O. I. Kolodiazhnyi,
10 Representative procedure: To a solution of phosphorane 4
(71.1 mg, 0.177 mmol) in THF (1.0 mL) was added a
suspension of NaH (60% in oil, 7.2 mg, 0.18 mmol) in THF
(1.0 mL) at 0 °C under nitrogen. After stirring for 1 h, PhCHO
(14.9 mg, 0.140 mmol) in THF (1.0 mL) was added, and the
resulting solution was stirred for another 3 h. The reaction
mixture was quenched with aq. NH4Cl, extracted with Et2O,
and the combined organic layer was washed with water
then brine, dried with MgSO4, and then concentrated. The
crude mixture was purified by PTLC (benzene) to give
PhCH=CHCO2Et (20.5 mg, 83%, Z:E = 96:4).
Chem. Lett. 2010, 39, 1138-1139
© 2010 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/