Stereoselective synthesis of vinyl-substituted (Z)-stilbenes by rhodium-catalysed addition of arylboronic acids to allenic alcohols

Article abstract of DOI:10.1039/c0ob00163e

Vinyl-substituted (Z)-stilbenes are stereoselectively synthesised on treatment of 4-arylbuta-2,3-dien-1-ols with arylboronic acids in the presence of a rhodium(i) catalyst. The reaction proceeds through the regioselective addition of organorhodium(i) species across the aryl-substituted carbon-carbon double bond of the allene moiety and subsequent δ-elimination of Rh(i)-OH.

Full text of DOI:10.1039/c0ob00163e

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Stereoselective synthesis of vinyl-substituted (Z)-stilbenes by
rhodium-catalysed addition of arylboronic acids to allenic alcohols†
Tomoya Miura, Hiroshi Shimizu, Tomohiro Igarashi and Masahiro Murakami*
Received 23rd May 2010, Accepted 29th June 2010
First published as an Advance Article on the web 26th July 2010
DOI: 10.1039/c0ob00163e
Vinyl-substituted (Z)-stilbenes are stereoselectively synthe-
sised on treatment of 4-arylbuta-2,3-dien-1-ols with aryl-
boronic acids in the presence of a rhodium(I) catalyst. The
reaction proceeds through the regioselective addition of
organorhodium(I) species across the aryl-substituted carbon–
carbon double bond of the allene moiety and subsequent d-
elimination of Rh(I)–OH.
(1)
species A is generated by transmetalation between Rh(I)–OH
and 2a. Regioselective syn addition of A across the phenyl-
substituted carbon–carbon double bond of 1a occurs from the
less-hindered side (a-side) to give the alkylrhodium(I) intermediate
B.11 We assume that attachment of rhodium(I) to the benzylic
position is favoured for the carborhodation of A, as with the
case of the rhodium-catalysed hydroarylation of styrene.12 Then,
intramolecular coordination of the hydroxy group to rhodium(I)
forms a six-membered ring rhodium(I) intermediate, for which two
half-chair conformations (C and D) are available. The intermediate
C having the phenyl substituent at the pseudo-equatorial position
is more stable than the other conformer D. The more stable
conformer C undergoes d-elimination of Rh(I)–OH with a double
bond shift to afford (Z)-isomer 3aa together with the catalytically
active Rh(I)–OH species.
Rhodium-catalysed addition reactions of organoboronic acids to
unsaturated functionalities have rapidly expanded as a powerful
tool for the construction of carbon–carbon bonds.1 Mechanis-
tically, an organorhodium(I) species is generated by transmet-
alation between Rh(I)–OR species (OR = hydroxy or alkoxy)
and organoboronic acids. It undergoes intermolecular addition
to various unsaturated organic compounds and, for the next part
of the catalytic cycle, the Rh(I)–OR species is regenerated typically
by two types of termination steps. One is protodemetalation with
H2O or ROH,2 and the other is b-elimination with an OR group
located b to rhodium(I) of an organorhodium(I) intermediate.3
We have developed a variety of rhodium-catalysed reactions
which proceed through a sequential addition/b-OR elimination
pathway.4 For example, the addition reaction of arylboroxines
onto cis-allylic diols gave 2-arylalk-3-en-1-ols.5 Herein, we report a
new addition reaction of organoboronic acids to allenic alcohols,
in which d-elimination of an Rh(I)–OH species occurs with an
organorhodium(I) adduct to give vinyl-substituted (Z)-stilbenes
stereoselectively.6,7
A solution of 4-phenylbuta-2,3-dien-1-ol (1a), o-tolylboronic
acid (2a, 1.0 equiv.) and a catalytic amount of [Rh(OH)(cod)]2
(5 mol% Rh, cod = cycloocta-1,5-diene) in MeOH (0.1 M) was
stirred for 3 h at room temperature. The allenic alcohol 1a was
consumed and chromatographic isolation afforded (Z)-vinyl-(2¢-
methyl)stilbene (3aa) in 61% yield with high stereoselectivity (Z/E
= 99 : 1, eqn (1)). The stereochemistry of the double bond was
confirmed by a difference NOE study. When the reaction was
carried out in the presence of ten equivalents of B(OH)3 as an
additive,8 the yield of 3aa was improved to 71%.‡ It is of interest
that the stereochemical outcome is opposite to that of the reaction
of 1a with 2a using a palladium catalyst; (E)-isomer 3aa was
selectively produced in the presence of Pd(PPh3)4.9
Scheme 1 Proposed reaction pathway
A variety of aryl- and alkenylboronic acids 2 were subjected to
the addition reaction to 1a (Table 1). The two other isomeric
tolylboronic acids 2b and 2c both afforded the corresponding
vinylstilbenes 3ab–3ac with high stereoselectivities (Z/E = >95 : 5,
entries 1 and 2). Not only electron-donating and -withdrawing
arylboronic acids 2e–2h but also heteroarylboronic acids 2i
and 2j were suitably reactive (entries 4–9). In addition, even
alkenylboronic acids 2k and 2l could participate in the addition
reaction (entries 10 and 11).
The stereoselective formation of (Z)-isomer 3aa can be ex-
plained by assuming a reaction pathway involving d-elimination of
Rh(I)–OH, as depicted in Scheme 1.10 Initially, o-tolylrhodium(I)
Department of Synthetic Chemistry and Biological Chemistry, Kyoto Uni-
versity, Katsura, Kyoto 615-8510, Japan. E-mail: murakami@sbchem.kyoto-
u.ac; Fax: +81 75 383 2748; Tel: +81 75 383 2747
† Electronic supplementary information (ESI) available: General experi-
mental information and spectral data. See DOI: 10.1039/c0ob00163e
4074 | Org. Biomol. Chem., 2010, 8, 4074–4076
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than to the cyclohexyl- or n-butyl-substituted double bond.13
Syn addition of A across the hydroxymethyl-substituted carbon–
carbon double bond occurs from the less-hindered side (d-side)
and b-elimination of Rh(I)–OH immediately follows to give (E)-5.
Table 1 Rh(I)-catalysed addition of aryl- and alkenylboronic acids 2 to
1aa
Entry
2
R
3
Yield/%b
Z/Ec
1
2
3
4
5
6
7
8
2b
2c
2d
2e
2f
2g
2h
2i
m-Tol
3ab
3ac
3ad
3ae
3af
3ag
3ah
3ai
68
77
68
76
68
71
73
61
71
52
68
>95 : 5
>95 : 5
95 : 5
>95 : 5
92 : 8
>95 : 5
>95 : 5
93 : 7d
94 : 6d
89 : 11
90 : 10
p-Tol
(2)
Ph
o-MeO–C6H4
p-MeO–C6H4
p-Br–C6H4
p-MeO2C–C6H4
2-thienyl
3-thienyl
b-styryl
9
10
11
2j
3aj
2k
2l
3ak
3al
In summary, we have developed a rhodium-catalysed addition
reaction of arylboronic acids to allenic alcohols, allowing the
stereoselective formation of vinyl-substituted (Z)-stilbenes. This
catalytic process presents a rare example of d-elimination of Rh(I)–
OH.
(E)-hexenyl
a Reactions conducted on a 0.2 mmol scale. b Isolated yield. c Determined
by 1H NMR. d In the absence of B(OH)3.
Table 2 Rh(I)-catalysed addition of o-tolylboronic acid (2a) to a-allenols
1a
Acknowledgements
Yield/%b Z/Ec
This work was supported in part by a Grant-in-Aid for Scientific
Research on Priority Areas “Chemistry of Concerto Catalysis”
No. 20037032 form MEXT, Japan.
Entry
1
1
3
46
62
>95 : 5d
Notes and references
‡ Typical procedure: An oven-dried flask was charged with 2a (27.1 mg,
0.20 mmol), B(OH)3 (123.6 mg, 2.0 mmol) and a solution of 1a (29.4 mg,
0.20 mmol) in MeOH (2.0 mL). Then, [Rh(OH)(cod)]2 (2.3 mg, 5.0 mmol)
was added and the flask was flushed with argon. After stirring at room
temperature for 3 h, the reaction mixture was diluted with ethyl acetate (10
mL) and passed through a pad of basic silica gel (Fuji Silysia Chemical
Ltd., NH-DM1020). The filtrate was concentrated under reduced pressure
and the residue was purified by preparative thin-layer chromatography
(hexane–ethyl acetate 50 : 1) to give the product 3aa as a colorless oil
(31.6 mg, 0.14 mmol, 71%, Z/E = 98 : 2).
2
91 : 9d
3
4
1d Ar = p-Cl–C6H4
1e Ar = p-MeO–C6H4 3ea
3da
68
61
>95 : 5
86 : 14
1 For reviews, see: (a) K. Fagnou and M. Lautens, Chem. Rev., 2003, 103,
169; (b) T. Hayashi and K. Yamasaki, Chem. Rev., 2003, 103, 2829; (c) T.
Miura and M. Murakami, Chem. Commun., 2007, 217; (d) S. W. Youn,
Eur. J. Org. Chem., 2009, 2597.
2 (a) T. Hayashi, M. Takahashi, Y. Takaya and M. Ogasawara, J. Am.
Chem. Soc., 2002, 124, 5052; (b) P. Zhao, C. D. Incarvito and J. F.
Hartwig, J. Am. Chem. Soc., 2007, 129, 1876.
a The reaction conditions were the same as those in Table 1. b Isolated yield.
c Determined by 1H NMR. d Using 2.5 equiv. of PhB(OH)2 for 24 h.
The use of other allenic alcohols 1 was also examined in
the rhodium-catalysed addition reaction of 2a (Table 2). Trisub-
stituted allenic alcohol 1b reacted to produce 3ba with high
stereoselectivity, albeit in low yield (Z/E = >95 : 5, entry 1).
Dimethyl-substituted substrate 1c was also converted to the
product 3ca in 62% yield (Z/E = 91 : 9, entry 2). Both chloro
and methoxy substituents were tolerated on the aryl substituent
of 1 (entries 3 and 4). The chloro-substituted allenic alcohol 1d
exhibited a higher stereoselectivity than the methoxy-substituted
allenic alcohol 1e.
For comparison, the reaction was carried out using alkyl-
substituted allenic alcohols 4. Much to our surprise, (E)-isomers 5
having the opposite stereochemistry were predominantly formed
(eqn (2)). The inversion of the stereochemistry is explained by
assuming that o-tolylrhodium(I) species A prefers addition to
the hydroxymethyl-substituted carbon–carbon double bond rather
3 (a) M. Lautens, C. Dockendorff, K. Fagnou and A. Malicki, Org.
Lett., 2002, 4, 1311; (b) L. Navarre, S. Darses and J.-P. Geneˆt, Chem.
Commun., 2004, 1108; (c) L. Dong, Y.-J. Xu, L.-F. Cun, X. Cui, A.-Q.
Mi, Y.-Z. Jiang and L.-Z. Gong, Org. Lett., 2005, 7, 4285; (d) B. P.
Machin, M. Ballantine, J. Mandel, N. Blanchard and W. Tam, J. Org.
Chem., 2009, 74, 7261.
4 (a) M. Murakami and H. Igawa, Helv. Chim. Acta, 2002, 85, 4182; (b) T.
Miura, M. Shimada and M. Murakami, J. Am. Chem. Soc., 2005, 127,
1094; (c) T. Miura, T. Sasaki, H. Nakazawa and M. Murakami, J. Am.
Chem. Soc., 2005, 127, 1390; (d) T. Miura, T. Sasaki, T. Harumashi and
M. Murakami, J. Am. Chem. Soc., 2006, 128, 2516; (e) T. Miura, M.
Shimada, S. Ku, T. Tamai and M. Murakami, Angew. Chem., Int. Ed.,
2007, 46, 7101.
5 T. Miura, Y. Takahashi and M. Murakami, Chem. Commun., 2007,
595.
6 For other synthetic methods of vinyl-substituted (Z)-stilbenes, see:
(a) K. K. Wang, C. Liu, Y. G. Gu, F. N. Burnett and P. D. Sattsangi,
J. Org. Chem., 1991, 56, 1914; (b) N. Chinkov, S. Majumdar and I.
Marek, J. Am. Chem. Soc., 2003, 125, 13258; (c) L. Shao and M. Shi,
Org. Biomol. Chem., 2005, 3, 1828.
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7 For synthetic applications of vinyl-substituted (Z)-stilbenes, see: (a) P.
Haeussinger and G. Kresze, Tetrahedron, 1978, 34, 689; (b) Y. Tamaru,
H. Satomi, O. Kitao and Z. Yoshida, Tetrahedron Lett., 1984, 25, 2561;
(c) C. S. Yi, Z. He and D. W. Lee, Organometallics, 2001, 20, 802.
8 (a) C. G. Frost, S. D. Penrose, K. Lambshead, P. R. Raithby, J. E.
Warren and R. Gleave, Org. Lett., 2007, 9, 2119; (b) H. Shimizu and
M. Murakami, Chem. Commun., 2007, 2855.
9 M. Yoshida, T. Gotou and M. Ihara, Chem. Commun., 2004, 1124.
10 An alternative mechanism involving allylic 1,3-migration of rhodium
with the intermediate B and subsequent b-elimination of Rh(I)–OH is
also conceivable. However, it is difficult to rationalise the stereoselective
formation of (Z)-isomer with this alternative mechanism.
11 For regioselective carbopalladation onto an allene moiety from the
less-hindered side, see: C. H. Oh, T. W. Ahn and R. Reddy, V., Chem.
Commun., 2003, 2622.
12 (a) M. Lautens, A. Roy, K. Fukuoka, K. Fagnou and B. Mart´ın-
Matute, J. Am. Chem. Soc., 2001, 123, 5358; (b) T. Miura, Y. Ito and
M. Murakami, Chem. Lett., 2008, 37, 1006.
13 For regiocontrolled addition to allenes depending on the transition
metal catalyst, see: (a) Y. Yamamoto, R. Fujikawa, A. Yamada and N.
Miyaura, Chem. Lett., 1999, 1069; (b) S. Onozawa, Y. Hatanaka and
M. Tanaka, Chem. Commun., 1999, 1863; (c) M. Yoshida, K. Matsuda,
Y. Shoji, T. Gotou, M. Ihara and K. Shishido, Org. Lett., 2008, 10,
5183.
4076 | Org. Biomol. Chem., 2010, 8, 4074–4076
This journal is
The Royal Society of Chemistry 2010
©