Rhodium-catalyzed asymmetric 1,4-addition to 1-alkenylphosphonates [13]

Full text of DOI:10.1021/ja993184u

J. Am. Chem. Soc. 1999, 121, 11591-11592
11591
Scheme 1
Rhodium-Catalyzed Asymmetric 1,4-Addition to
1-Alkenylphosphonates
Tamio Hayashi,* Taichi Senda, Yoshiaki Takaya, and
Masamichi Ogasawara
Department of Chemistry, Graduate School of Science
Kyoto UniVersity, Sakyo, Kyoto 606-8502, Japan
ReceiVed September 3, 1999
Optically active phosphonic acid derivatives are important
compounds because of their synthetic utility as chiral building
blocks1 as well as their potential biological activity.2 Asymmetric
1,4-addition of organometallic reagents to R,â-unsaturated com-
pounds is a powerful tool for carbon-carbon bond formation with
simultaneous introduction of a new stereogenic carbon center at
the â-position. Although many papers have appeared on the topic
of catalytic asymmetric 1,4-addition to R,â-unsaturated carbonyl
compounds with high enantioselectivity,3 to our best knowledge
the enantioselective reaction to R,â-unsaturated phosphonates has
not been reported yet,4,5 probably due to their low reactivity
toward the 1,4-addition. Recently, we found asymmetric 1,4-
addition of aryl- and alkenylboronic acids to R,â-unsaturated
ketones which proceeds with high enantioselectivity under
catalysis by a chiral phosphine-rhodium complex.6 Here we
report that the rhodium-catalyzed asymmetric 1,4-addition is
successfully applied to R,â-unsaturated phosphonates7 by use of
triarylcyclotriboroxanes as arylating reagents in place of arylbo-
ronic acids.
We prepared geometrically pure diethyl (E)- and (Z)-1-
propenylphosphonates (1a) by the palladium-catalyzed cross-
coupling type reaction8 of diethyl phosphite with (E)- and (Z)-
1-propenyl bromide, respectively. Treatment of the R,â-unsaturated
phosphonate with phenylboronic acid under the conditions previ-
ously reported6 for R,â-unsaturated ketones gave a poor yield of
diethyl 2-phenylpropylphosphonate (3am, Scheme 1). For ex-
ample, the reaction of (E)-1a with phenylboronic acid in the
presence of 3 mol % of the catalyst generated from Rh(acac)-
(C2H4)2 and (S)-binap in dioxane/H2O (10/1) at 100 °C for 5 h
gave 3am (84% ee) only in 44% yield (entry 1 in Table 1). It
was found that the rhodium catalyst loses its catalytic activity
within 30 min under the conditions described above and that the
presence of a large amount of water as a cosolvent causes the
Table 1. Asymmetric 1,4-Addition of Arylboroxines 2 to
1-Alkenylphosphonates 1 Catalyzed by (S)-binap-Rhodium(I)a
phosphonate
yieldb (%)
[R]20
D
entry
1
(ArBO)3 2
of 3
% eec (c in CHCl3)
1d
2
(E)-1a
(E)-1a
(E)-1a
(E)-1a
(E)-1a
(E)-1a
(E)-1a
(E)-1a
(E)-1a
(E)-1a
(E)-1a
(E)-1b
(E)-1c
(E)-1c
(E)-1d
(Z)-1a
(Z)-1a
(Z)-1a
PhB(OH)2
2m
2m
p-TolB(OH)2 43 (3an) 86
2n
2n
2o
2p
2q
44 (3am) 84 (S)
94 (3am) 96 (S) -19 (0.93)
5 (3am)
3e
4d
5
84 (3an) 95
88 (3an) 96
64 (3ao) 96
61 (3ap) 96
81 (3aq) 95
89 (3ar) 89
92 (3ar) 90
96 (3bm) 94
-23 (0.98)
6f
7
8
9
-25 (0.86)
-24 (0.72)
-21 (0.92)
-21 (1.01)
10
11f
12
13
14f
15
16
17g
18f
2r
2r
2m
2m
2m
2m
2m
2m
2m
-25 (1.07)
95 (3cm) 91 (S) -16 (1.10)
99 (3cm) 94 (S)
39 (3dm) 99
96 (3am) 89 (R) +18 (1.13)
23 (3am) 97 (R)
-10 (1.03)
98 (3am) 92 (R)
a The reaction was carried out with phosphonate 1 (0.20 mmol),
arylboroxine 2 (0.67 mmol), and H2O (2.0 mmol) in dioxane (0.8∼1.0
mL) at 100 °C for 3 h in the presence of 3 mol % of the catalyst
generated from Rh(acac)(C2H4)2 and (S)-binap unless otherwise noted.
b Isolated yield by silica gel chromatography. c Determined by HPLC
analysis with chiral stationary phase columns: Daicel Chiralcel AD
(3am, 3an, 3ao, 3ap, 3aq, 3ar, 3bm) (eluent, hexane/2-propanol )
98/2), OD-H (3cm) (eluent, hexane/2-propanol ) 90/10), and OJ (3dm)
(eluent, hexane/2-propanol ) 98/2). d Reaction of ArB(OH)2 in dioxane/
H2O (10/1). e Reaction without addition of H2O. f As a chiral ligand,
(S)-u-binap was used in place of (S)-binap. g Reaction was stopped at
the reaction period of 3 min.
(1) For a review on the use of phosphonates for alkene synthesis, see: Kelly,
S. E. In ComprehensiVe Organic Synthesis; Trost, B. M., Fleming, I., Eds.;
Pergamon: Oxford, 1991; Vol. 1, Chapter 3.1.
(2) For examples of asymmetric synthesis of biologically active phospho-
nates, see: (a) Blazis, V. J.; Koeller, K. J.; Spilling, C. D. J. Org. Chem.
1995, 60, 931. (b) Arai, T.; Bougauchi, M.; Sasai, H.; Shibasaki, M. J. Org.
Chem. 1996, 61, 2926 and references therein. (c) Nagaoka, Y.; Tomioka, K.
J. Org. Chem. 1998, 63, 6428.
(3) For reviews, see: (a) Schmalz, H.-G. In ComprehensiVe Organic
Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon: Oxford, 1991; Vol. 4,
Chapter 1.5. (b) Rossiter, B. E.; Swingle, N. M. Chem. ReV. 1992, 92, 771.
(c) Noyori, R. Asymmetric Catalysis in Organic Synthesis; John Wiley and
Sons: New York, 1994; pp 207-212. (d) No´gra´di, M. StereoselectiVe
Synthesis; VCH Publishers: New York, 1995; pp 213-224. (e) Seyden-Penne,
J. Chiral Auxiliaries and Ligands in Asymmetric Synthesis; John Wiley and
Sons: New York, 1995.
(4) For a review on 1,4-addition reactions, see: Perlmutter, P. Conjugate
Addition Reactions in Organic Synthesis; Pergamon Press: Oxford, 1992.
(5) For an example of nonasymmetric addition of alkyl- and vinylcopper
reagents to R,â-unsaturated phosphonates, see: Nicotra, F.; Panza, L.; Russo,
G. J. Chem. Soc., Chem. Commun. 1984, 5.
catalyst deactivation. The asymmetric 1,4-addition was greatly
improved by carrying out the reaction with triphenylcyclotri-
boroxane (phenylboroxine, (PhBO)3)9 (2m) in place of phenyl-
boronic acid (entry 2). Thus, the reaction of (E)-1a with
phenylboroxine (2m) and 1 equiv (to boron) of water in dioxane
at 100 °C for 3 h gave 94% yield of 3am ([R]20 -19 (c 0.93,
D
chloroform)), whose enantiomeric purity was determined to be
96% ee by HPLC analysis with a chiral stationary phase column
(entry 2). The absolute configuration of (-)-3am was assigned
to be S by correlation with (+)-(R)-1,3-diphenyl-1-butene (4)10
(6) (a) Takaya, Y.; Ogasawara, M.; Hayashi, T.; Sakai, M.; Miyaura, N. J.
Am. Chem. Soc. 1998, 120, 5579. (b) Takaya, Y.; Ogasawara, M.; Hayashi,
T. Tetrahedron Lett. 1998, 39, 8479.
(7) For a review on vinylphosphonates in organic synthesis, see: Minami,
T.; Motoyoshiya, J. Synthesis 1992, 333.
(8) Hirao, T.; Masunaga, T.; Yamada, N.; Ohshiro, Y.; Agawa, T. Bull.
Chem. Soc. Jpn. 1982, 55, 909.
(9) Arylboroxines are readily obtained by dehydration of arylboronic acids
by azeotropic removal of water from their xylene solution or heating at 300
°C in vacuo. For a pertinent review, see: Lappert, M. F. Chem. ReV. 1956,
56, 959.
10.1021/ja993184u CCC: $18.00 © 1999 American Chemical Society
Published on Web 11/24/1999

11592 J. Am. Chem. Soc., Vol. 121, No. 49, 1999
Communications to the Editor
(vide infra). The addition of 1 equiv of water is essential for the
high yield,11 almost no reaction taking place in the absence of
water (entry 3).
Scheme 2a
Under similar reaction conditions, diethyl (E)-1-propenylphos-
phonate ((E)-1a) underwent asymmetric arylation with some other
arylboroxines (2n-2r) to give the corresponding diethyl 2-aryl-
propylphosphonates (3an-3ar) in good yields with high enan-
tioselectivity (entries 5, and 7-10). Here, again, the yield of 3an
was much lower in the reaction with p-tolylboronic acid than with
p-tolylboroxine (entries 4 and 5). The asymmetric phenylation
was also successful for dimethyl and diphenyl esters of (E)-1-
propenylphosphonate ((E)-1b,c) (entries 12 and 13). The enan-
tioselectivities and chemical yields were slightly higher in the
reaction catalyzed by rhodium complex coordinated with unsym-
metrically substituted binap ligand, (S)-u-binap,12 which has
diphenylphosphino and bis(3,5-dimethyl-4-methoxyphenyl)phos-
phino groups at the 2 and 2′ positions on the 1,1′-binaphthyl
skeleton (entries 6, 11, and 14).
The rhodium-catalyzed asymmetric phenylation of the Z isomer
of diethyl 1-propenylphosphonate (Z)-1a with phenylboroxine 2m
for 3 h gave the R isomer of 3am with 89% ee (entry 16). The
observation of the opposite absolute configuration of 3am for
(E)-1a and (Z)-1a indicates that the dialkoxyphosphinyl moiety
on the 1-alkenylphosphonate plays a key role in the enantioface
selection (Scheme 2). The (S)-binap-rhodium catalyst recognizes
the enantioface of 1-propenylphosphonate by the steric bulkiness
of the phosphinyl group; both (E)-1a and (Z)-1a phenylated on
the rhodium from the 1si face irrespective of the E,Z geometry
of the 1-propenyl moiety.13 The Z isomer (Z)-1a was found to
undergo slow isomerization into the E isomer under these
reactions conditions, resulting in the loss of enantioselectivity.
This was demonstrated by stopping the reaction at the reaction
period of 3 min, which gave 3am of 97% ee (entry 17).
The optically active alkylphosphonates 3, containing the
stereogenic carbon center at the â-position, can be used as chiral
building blocks for the synthesis of optically active alkenes by
the Horner-Emmons type reaction (Scheme 3). The olefination
of carbonyl compounds with diphenyl phosphonates proceeded
without loss of enantiomeric purity. Unfortunately, the elimination
forming alkenes did not take place from the â-hydroxyphospho-
a The binaphthylene moiety in (S)-binap is omitted for clarity.
Scheme 3
nate intermediates in the reaction of diethyl phosphonates,14 but
diethyl esters were readily converted into diphenyl esters by way
of dichlorides.15 For example, the ester substitution of (-)-3am
(91% ee) from ethyl to phenyl followed by treatment of the
resulting diphenyl ester (-)-3cm with tert-butyllithium and
benzaldehyde gave (+)-(R)-(E)-1,3-diphenyl-1-butene (4a)10 of
92% ee,16 together with a minor amount of (Z)-isomer (E/Z )
82/18), indicating that the absolute configuration of 3am and 3cm
is (-)-(S). Similarly, the reaction of (-)-3cm with benzophenone
gave (-)-(R)-1,1,3-triphenyl-1-butene (4b)17 of 91% ee.16
To summarize, we have realized, for the first time, the catalytic
asymmetric 1,4-addition to 1-alkenylphosphonates, forming
2-arylalkylphosphonates in high yields with high enantioselec-
tivity, by use of a new catalytic system consisting of a chiral
phosphine-rhodium catalyst and arylboroxines as arylating
reagents.
(10) Hayashi, T.; Konishi, M.; Fukushima, M.; Mise, T.; Kagotani, M.;
Tajika, M.; Kumada, M. J. Am. Chem. Soc. 1982, 104, 180.
(11) Interestingly, the rhodium-catalyzed reaction of (E)-1a with phenyl-
boronic acid in nonaqueous dioxane, namely, in the absence of water, resulted
in a lower yield (67%) of 3am (88% ee), though a boronic acid is known to
be in equilibrium with a boroxine and water (ref 9). Methanol can also be
used in place of water as a protic additive to phenylboroxine (85% yield of
3am), while the reaction with dimethyl ester (PhB(OMe)2) did not take place
(<2% yield).
Acknowledgment. This work was supported by “Research for the
Future” Program, the Japan Society for the Promotion of Science, and a
Grant-in-Aid for Scientific Research, the Ministry of Education, Japan.
Supporting Information Available: Experimental procedures and
spectroscopic and analytical data for the substrates and products (PDF).
This material is available free of charge via the Internet at http://pubs.acs.org.
(12) The new chiral bisphosphine (S)-u-binap was prepared starting from
(S)-binaphthol ditriflate by a sequence of reactions consisting of palladium-
catalyzed monophosphinylation with bis[(3,5-dimethyl-4-methoxy)phenyl]-
phosphine oxide, reduction of the phosphine oxide with trichlorosilane and
triethylamine, and nickel-catalyzed cross-coupling of the remaining triflate
JA993184U
(14) Corey, E. J.; Kwiatkowski, G. T. J. Am. Chem. Soc. 1966, 88, 5654.
(15) Ando, K. Tetrahedron Lett. 1995, 36, 4105.
with diphenylphosphine in 74% overall yield: [R]20 -103 (c 1.08, chloro-
D
form).
(16) The enantiomeric purities of (E)-4a and -4b were determined by GLC
(13) For the highly skewed structure of transition metal complexes
coordinated with a binap ligand, see: Ozawa, F.; Kubo, A.; Matsumoto, Y.;
Hayashi, T. Organometallics 1993, 12, 4188 and references therein.
analysis with CP-Chirasil-dex CB (25 m).
(17) [R]20 -73 (c 0.52, chloroform). The absolute configuration was
D
assigned by the correlation with the starting (-)-(S)-3cm.