Organo[2-(hydroxymethyl)phenyl]dimethylsilanes as mild and reproducible agents for rhodium-catalyzed 1,4-addition reactions

Article abstract of DOI:10.1021/ja071969r

Stable and reusable tetraorganosilicon reagents, alkenyl-, aryl-, and silyl[2-(hydroxymethyl)phenyl]-dimethylsilanes, undergo 1,4-addition reactions to α,β-unsaturated carbonyl acceptors under mild rhodium-catalysis. The reaction tolerates a diverse range of functional groups and is applicable to gram-scale synthesis. Use of a chiral diene ligand allows the achievement of the corresponding enantioselective transformations using the tetraorganosilicon reagents, providing the silicon-based approach to optically active ketones and substituted piperidones that serve as synthetic intermediates of pharmaceuticals. A rhodium alkoxide species is suggested to be responsible for a transmetalation step on the basis of the observed kinetic resolution of a racemic chiral phenylsilane in the enantioselective 1,4-addition reaction under the rhodium-chiral diene catalysis.

Full text of DOI:10.1021/ja071969r

Published on Web 06/30/2007
Organo[2-(hydroxymethyl)phenyl]dimethylsilanes as Mild and
Reproducible Agents for Rhodium-Catalyzed 1,4-Addition
Reactions
Yoshiaki Nakao,*,† Jinshui Chen,† Hidekazu Imanaka,† Tamejiro Hiyama,*,†
Yoshitaka Ichikawa,‡ Wei-Liang Duan,‡ Ryo Shintani,‡ and Tamio Hayashi*,‡
Contribution from the Department of Material Chemistry, Graduate School of Engineering,
Kyoto UniVersity, Kyoto 615-8510, Japan, and Department of Chemistry, Graduate School of
Science, Kyoto UniVersity, Kyoto 606-8502, Japan
Received March 20, 2007; E-mail: nakao@npc05.kuic.kyoto-u.ac.jp; thiyama@npc05.kuic.kyoto-u.ac.jp; thayashi@kuchem.kyoto-u.ac.jp
Abstract: Stable and reusable tetraorganosilicon reagents, alkenyl-, aryl-, and silyl[2-(hydroxymethyl)phenyl]-
dimethylsilanes, undergo 1,4-addition reactions to R,â-unsaturated carbonyl acceptors under mild rhodium-
catalysis. The reaction tolerates a diverse range of functional groups and is applicable to gram-scale
synthesis. Use of a chiral diene ligand allows the achievement of the corresponding enantioselective
transformations using the tetraorganosilicon reagents, providing the silicon-based approach to optically
active ketones and substituted piperidones that serve as synthetic intermediates of pharmaceuticals. A
rhodium alkoxide species is suggested to be responsible for a transmetalation step on the basis of the
observed kinetic resolution of a racemic chiral phenylsilane in the enantioselective 1,4-addition reaction
under the rhodium-chiral diene catalysis.
Introduction
silanes, organosilanediols, and chlorosilanes in excess under
relatively harsh conditions. Furthermore, use of highly nucleo-
philic activators including metal fluorides in a stoichiometric
amount is essential in some cases3f,5f,h,l,m to activate the silicon
reagents to be reactive enough and undergo transmetalation to
rhodium(I) or palladium(II) species. Thus, the development of
new silicon reagents that are highly stable but reactive enough
at the same time have remained elusive.
Transition metal-catalyzed addition reactions of organome-
tallic reagents to electron-deficient olefins have attracted much
attention and have been developed extensively in the past
decade. Especially, since the landmark report by Miyaura and
co-workers in 1997,1 use of organoboron reagents has found
many synthetic applications including asymmetric synthesis
because of their tolerance toward many functional groups as
well as easy handling and ready availability.2-4 Alternative
organometallic reagents have also been developed including
silicon,3d,f,5 titanium,6 zinc,7 zirconium,8 indium,9 tin,10 lead,11
and bismuth.12 Among these, organosilicon reagents should have
significant importance in view of stability and nontoxicity as
well as natural abundance of silicon element. Nevertheless,
reported examples of such silicon-based reactions rely on the
use of acid-, base-, and/or moisture-sensitive organotri(alkoxy)-
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Lett. 2003, 5, 97. (d) Otomaru, Y.; Hayashi, T. Tetrahedron: Asymmetry
2004, 15, 2647. (e) Oi, S.; Taira, A.; Honma, Y.; Sato, T.; Inoue, Y.
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T.-S.; Li, C.-J. Chem. Commun. 2001, 2348. Organosilicones: (j) Koike,
T.; Du, X.; Mori, A.; Osakada, K. Synlett 2002, 301. For palladium-
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Chem. Commun. 2007, 710. See also ref 3d and ref 3f.
† Graduate School of Engineering.
‡ Graduate School of Science.
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9
10.1021/ja071969r CCC: $37.00 © 2007 American Chemical Society
J. AM. CHEM. SOC. 2007, 129, 9137-9143
9137

A R T I C L E S
Nakao et al.
Of many types of organosilicon compounds, tetraorganosi-
lanes should be ideal in view of their high stability. As is the
case with ubiquitous triorganosilyl protecting groups, alkenyl-
and aryltriorganosilanes survive many synthetic transformations,
allowing their installation at even an early stage of complex
natural product syntheses.13 A wide range of (E)-, (Z)-, and
R-substituted triorgano(vinyl)silanes are readily available by
virtue of recent progress in transition metal-catalyzed hydro-
silylation of alkynes.14 Whereas a classical strategy involving
transmetalation between aryl-Grignard or -lithium reagents with
triorganosilyl halides still serves as a convenient access to simple
aryltriorganosilanes, the metal-catalyzed cross-coupling reactions
of aryl halides with disilanes15 or hydrosilanes16 and direct
silylation of Ar-H bonds17 have gained significant synthetic
value as highly chemoselective and atom economical alternatives
to classical syntheses of arylsilanes. In light of the growing
importance of silicon-based transformations, we have recently
disclosed that organo[2-(hydroxymethyl)phenyl]dimethylsilanes
(1) behave as a new class of silicon reagents for the palladium-
catalyzed cross-coupling reaction.18 The reagents allow chemi-
cally stable tetraorganosilicon compounds19 to participate in the
cross-coupling chemistry under fluoride-free conditions for the
first time with excellent chemoselectivities. The proximal
hydroxyl group is supposed to coordinate to the nearby silicon
atom upon treatment with a mild base, such as K2CO3, to
produce a requisite five-membered pentacoordinated silicate
species.18 With the given success of the silicon reagents 1 in
the cross-coupling chemistry, we envisioned the use of 1 as a
Figure 1. Conversion vs time for the reactions of a phenylmetal reagent
([Ph-M]0 ) 67 mM) with methyl vinyl ketone ([2a]0 ) 201 mM) in the
presence of a rhodium catalyst ([Rh]total ) 2.7 mM) at 30 or 50 °C: (a)
PhB(OH)2 as the nucleophile and [Rh(OH)(cod)]2 as the catalyst in 1,4-
dioxane/H2O (10/1) at 30 °C in the presence of [B(OH)3]0 ) 536 mM (for
the reaction conditions, see ref 21); (b) 1a as the nucleophile and [Rh-
(OH)(cod)]2 as the catalyst in 1,4-dioxane at 50 °C; (c) 1a as the nucleophile
and [Rh(OH)(cod)]2 as the catalyst in THF at 30 °C; (d) PhSi(OMe)3 as
the nucleophile and [Rh(cod)(MeCN)2]BF4 as the catalyst in 1,4-dioxane/
H2O (10/1) at 50 °C.
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Chem. Soc. 2005, 127, 6952. (b) Nakao, Y.; Sahoo, A. K.; Yada, A.; Chen,
J.; Hiyama, T. Sci. Technol. AdV. Mater. 2006, 7, 536. (c) Nakao, Y.;
Imanaka, H.; Chen, J.; Yada, A.; Hiyama, T. J. Organomet. Chem. 2007,
692, 585. (d) Nakao, Y.; Ebata, S.; Chen, J.; Imanaka, H.; Hiyama, T.
Chem. Lett. 2007, 606. For use of these reagents for allylation of aldehydes,
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new entry to silicon-based rhodium-catalyzed 1,4-addition
reactions. We report herein full details of the rhodium-catalyzed
transformations using 1 under mild conditions without any
activators to produce a wide range of adducts in good yields
with excellent chemoselectivities. Enantioselective 1,4-addition
reactions are also demonstrated by the aid of rhodium/chiral
diene catalysis.
Results and Discussion
Rhodium-Catalyzed 1,4-Addition Reactions of Organo-
[2-(hydroxymethyl)phenyl]dimethylsilanes. At the onset, we
assessed the reactivity of 1 by the reaction of phenyl[2-
(hydroxymethyl)phenyl]dimethylsilane (1a) with an excess
amount of methyl vinyl ketone (2a) in the presence of [Rh-
(OH)(cod)]2 as a catalyst (eq 1). The reaction was carried out
in 1,4-dioxane at 30 °C and monitored in a reaction calorimetry
(Omnical SuperCRC).20 Almost quantitative conversion of 1a
was observed after 3 h (curve c, Figure 1), whereas the reaction
trimethoxy(phenyl)silane, a representative silicon reagent fre-
quently used for rhodium-catalyzed transformations,5a-g in the
presence of cationic Rh(cod)(MeCN)2BF4 as a catalyst in 1,4-
dioxane/H2O (10/1)5a showed less than 10% yield of 1,4-adduct
(20) For a review on kinetic studies using calorimetry, see: Blackmond, D. G.
Angew. Chem., Int. Ed. 2005, 44, 4302.
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9138 J. AM. CHEM. SOC. VOL. 129, NO. 29, 2007

Organo[2-(hydroxymethyl)phenyl]dimethylsilanes
A R T I C L E S
1
3aa by H NMR analysis even at 50 °C (curve d), and no
hydroxyl, giving various 3-alkenylcyclohexanones in good yields
(entries 6-12). Conjugated 1,3-dienylsilane 1p, (E)-styrylsilane
1q, and (Z)-propenylsilane 1r added to 2b with retention of the
olefinic configuration (entries 13-15). (Z)-Styrylsilane (1s) also
gave 3sb as a major product (∼95%) albeit being contaminated
by a small amount (∼5%) of its stereoisomer 3qb (entry 16).22
Ethenylsilanes having substituent(s) like 1-methyl, 1-phenyl, 2,2-
dimethyl, and (E)-1,2-dipropyl participated in the reaction with
2b with perfect regio- and stereospecificities in good yields
(entries 17-20). Especially, successful addition of R-substituted
vinylsilanes, 1t and 1u, is worth noting, because the corre-
sponding vinylboronic acids are relatively unstable thermally23
and, thus, have rarely been employed in the rhodium-catalyzed
transformations.
We also applied the present protocol to 1,4-addition of a silyl
group to enones.24 Disilane reagent 5 was prepared by the
reaction of cyclic silyl ether 4 with dimethylphenylsilyllithium
and was subjected to the reaction with 2b using 1,3-bis-
(diphenylphosphino)propane (dppp) as a ligand (eq 2).24a Desired
adduct 6 was obtained in 66% yield, although extra loading of
5 (3.5 molar equiv to 2b) was necessary because of competitive
protonolysis of the dimethylphenylsilyl group of 5 leading to
dimethylphenylsilane as a byproduct. The formation (88% yield)
of silicon residue 4 was confirmed by GC analysis of the crude
mixture.
reaction was observed by the use of [Rh(OH)(cod)]2 as a
catalyst. We further found that the rate of the reaction using 1a
at 50 °C was comparable with that using phenylboronic acid21
at 30 °C (curve a vs curve b). Apparently, these results indicated
an enhanced reactivity of organo[2-(hydroxymethyl)phenyl]-
dimethylsilanes as alternatives of organoboronic acids, compared
with conventional silicon reagents such as trialkoxy(organo)-
silanes.
Indeed, the equimolar reaction of 1a with 2a with a 1.0 mmol
scale in the presence of [Rh(OH)(cod)]2 (1.0 mol % Rh) in THF
at 35 °C gave 3aa in 94% yield after 4 h (entry 1 of Table 1
using). The observed excellent reactivity of the silicon reagent
under mild conditions prompted us to further investigate the
scope of both silicon reagents and electrophiles. The addition
of 1a across 2-cyclohexen-1-one (2b) also took place smoothly
under the identical conditions to give 3-phenylcyclohexanone
(3ab) in 90% yield (entry 2). The same reaction on a gram-
scale (10 mmol scale) allowed us to isolate cyclic silyl ether 4,
a silicon residue of the reaction, in 92% yield by distillation of
the crude product and 3ab in 92% yield by flash chromatography
on silica gel of the residue (entry 3). As we have already
demonstrated that 4 serves as a silylating agent of various aryl-
Grignard reagents to give the arylsilane reagents employed in
this study,18a,b the metal residue of the 1,4-addition reaction is
demonstrated to be reproducible for the first time. Reactions of
1a met success not only with cyclic or acyclic enones (entries
4-6) but also with various R,â-unsaturated esters, amides, and
nitrile in good yields (entries 7-14). Phenylsilanes having
methoxy (1b), fluoro (1c), bromo (1d), cyano (1e), and
pinacolatoboryl (1f) at the para position all reacted with 2b,
these functional groups being intact during the reactions (entries
15-19). Sterically highly demanding 2,4,6-trimethylphenylsi-
lane (1g) gave the corresponding adduct 3gb in 85% yield
although extra loading of the arylsilane reagent (total 1.5 equiv)
was necessary (entry 20). In sharp contrast to the transmetalation
of arylsilanes 1 to a palladium(II) complex which requires the
use of a copper(I) cocatalyst for the success of cross-
coupling,18a,b it should be noted that transmetalation to rhodium-
(I) proceeds very efficiently without the aid of other metal
cocatalyst.
We then examined the 1,4-addition reaction using alkenyl-
silanes (Table 2). The stoichiometric reaction (1.0 mmol scale)
of (E)-[2-(hydroxymethyl)phenyl]dimethyl(1-octenyl)silane (1h)
with 2a in the presence of [Rh(OH)(cod)]2 (1.0 mol % Rh) in
THF at 35 °C gave the corresponding adduct 3ha in 67% yield
after 4 h (entry 1 of Table 2). The reaction of 1h with 2b
proceeded successfully irrespective of its reaction scale (entries
2 and 3), and cyclic silyl ether 4 was again recovered in 80%
yield (entry 3). Reusability of 4 for preparation of the alkenyl-
silane reagents has been demonstrated previously.18a,c Cyclic
enones, 2c and 2d, also underwent the 1,4-addition reaction of
1h to give the corresponding adducts in good yields (entries 4
and 5). We then surveyed the scope of alkenylsilanes, which
were obtained readily by platinum-catalyzed hydrosilylation of
the corresponding alkynes.18a,c Excellent chemoselectivity was
observed with (E)-alkenylsilanes having a functional group, such
as cyano, ester, chloro, siloxy, malonate, phthalimide, or free
Enantioselective 1,4-Addition Reactions of Organo[2-
(hydroxymethyl)phenyl]dimethylsilanes. The success with the
1,4-addition reactions of the silicon reagents under mild reaction
conditions encouraged us to turn our attention to the application
of 1 to asymmetric synthesis. The recent innovation in the highly
reactive and enantioselective rhodium-catalysis with chiral diene
ligands25-27 prompted us to utilize this chemistry for the
asymmetric transformations using 1. Thus, the equimolar
reaction of phenylsilane 1a with 2b in the presence of [RhCl-
(C2H4)]2 (3.0 mol % Rh), (1R,4R)-2,5-diphenylbicyclo[2.2.2]-
(22) The isomer would be derived from partial isomerization of (Z)-styrylrhodium
intermediate via a plausible rhodium carbene species. For a related
isomerization in the rhodium-catalyzed hydrosilylation of alkynes, see:
Ojima, I.; Clos, N.; Donovan, R. J.; Ingallina, P. Organometallics 1990, 9,
3127.
(23) Peyroux, E.; Berthiol, F.; Doucet, H.; Santelli, M. Eur. J. Org. Chem. 2004,
1075.
(24) Recently, Oestreich and coworkers have reported rhodium-catalyzed
1,4-addition reactions of silylboranes, see: (a) Walter, C.; Auer, G.;
Oestreich, M. Angew. Chem., Int. Ed. 2006, 45, 5675. For 1,4-addition
reactions of disilanes across R,â-unsaturated compounds using palladium
or copper catalysts, see: (b) Hayashi, T.; Matsumoto, Y.; Ito, Y.
Tetrahedron Lett. 1988, 29, 4147. (c) Hayashi, T.; Matsumoto, Y.; Ito, Y.
J. Am. Chem. Soc. 1988, 110, 5579. (d) Matsumoto, Y.; Hayashi, T.; Ito,
Y. Tetrahedron 1994, 50, 335. (e) Ito, H.; Ishizuka, T.; Tateiwa, J.-i.;
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2004, 126, 84.
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A R T I C L E S
Nakao et al.
Table 1. Rhodium-Catalyzed 1,4-Addition Reactions of Aryl[2-(hydroxymethyl)phenyl]dimethylsilanes to Electron-Deficient Olefinsa
a Unless otherwise noted, the reaction was carried out in THF (0.5 mL) using an arylsilane (1.0 mmol) and an electrophile (1.0 mmol) in the presence of
[Rh(OH)(cod)]2 (1.0 mol % Rh) at 35 °C. b Isolated yields. c The reaction was carried out on a 10 mmol scale. d Cyclic silyl ether 4 was also isolated in 92%
yield. e The reaction was carried out using [Rh(OH)(cod)]2 (3.0 mol % Rh) at 50 °C. f The reaction was carried out using 1.2 mmol of 1a. g The reaction was
carried out using 1.3 mmol of 1a at 60 °C. h The reaction was carried out using 1.5 mmol of 1g.
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Organo[2-(hydroxymethyl)phenyl]dimethylsilanes
A R T I C L E S
Table 2. Rhodium-Catalyzed 1,4-Addition Reactions of Alkenyl[2-(hydroxymethyl)phenyl]dimethylsilanes to Cyclic Enonesa
a Unless otherwise noted, the reaction was carried out in THF (0.5 mL) using an alkenylsilane (1.0 mmol) and an enone (1.0 mmol) in the presence of
[Rh(OH)(cod)]2 (1.0 mol % Rh) at 35 °C. b Isolated yields. c The reaction was carried out on a 10 mmol scale. d Cyclic silyl ether 4 was also isolated in 80%
yield. e Contaminated by 5% of 3qb.
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A R T I C L E S
Nakao et al.
Table 3. Rhodium-Catalyzed Enantioselective 1,4-Addition Reactions of Organo[2-(hydroxymethyl)phenyl]dimethylsilanesa
a
Unless otherwise noted, the reaction was carried out in THF (0.30 mL) using an organosilane (0.30 mmol) and an electrophile (0.30 mmol) in the
presence of [RhCl(C2H4)]2 (3.0 mol % Rh), a diene ligand (3.3 mol %), and 1.0 M KOH aq (15 mol %) at 40 °C. b Isolated yields. c Determined by chiral
HPLC with hexane/2-propanol. d The reaction was carried out at 50 °C using [RhCl(C2H4)]2 (5.0 mol % Rh) and 1.5 equiv of 1c. e The reaction was carried
out at 50 °C using 1.5 equiv of 1x. f The reaction was carried out using 1.5 equiv of 1t. g The reaction was carried out using 5.0 mol % Rh. h Determined
by converting it to an acetal of (R,R)-1,2-diphenylethanediol.
octa-2,5-diene [(R,R)-Ph-bod*] (3.3 mol %),26 and a 1.0 M
aqueous solution of KOH (15 mol %) in THF at 40 °C for 10
h gave (R)-3ab of 97% ee in 93% yield (entry 1 of Table 3).
The enantioselective addition of 1a to 2c was also achieved
under the identical conditions, affording (R)-3ac with 99% ee
(entry 2). Employing (1R,4R)-2,5-dibenzylbicyclo[2.2.2]octa-
2,5-diene [(R,R)-Bn-bod*] as a ligand instead of (R,R)-Ph-bod*,
acyclic enones 2n and 2o underwent the 1,4-addition of 1a to
give the corresponding adducts (R)-3an and (S)-3ao with
excellent enantioselectivities (entries 3 and 4). Furthermore, the
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9142 J. AM. CHEM. SOC. VOL. 129, NO. 29, 2007

Organo[2-(hydroxymethyl)phenyl]dimethylsilanes
A R T I C L E S
Scheme 1. Plausible Mechanism
give Michael adduct 3 and rhodium alkoxide D. Transmetalation
of R from silicon to rhodium would take place by the aid of
the proximal hydroxyl group to regenerate B to complete the
cycle. To gain a mechanistic insight into the transmetalation
step, we examined the enantioselective addition of 2.0 molar
equiv of racemic chiral phenylsilane reagent 1z to 2b using Rh/
(R,R)-Bn-bod* to give the corresponding adduct (R)-3ab of 95%
ee in 87% yield, and unreacted (R)-1z of 52% ee was recovered
in 54% yield based on the amount of loaded 1z (eq 3).31 The
observed kinetic resolution of 1z clearly supports that rhodium
alkoxide species D would be responsible for the transmetalation
step, recognizing the chirality of 1z effectively by the optically
pure diene ligand. Intermolecular transfer of the R group via
pentacoordinated silicate intermediate E appears to be less
plausible in this particular transformation.32
reactions of arylsilane 1c or 1x with nitrogen-containing
substrates 2p or 2q provided a silicon-based approach to
optically-active substituted piperidones, (R)-3cp28 or (R)-3xq,7
respectively (entries 5 and 6). (R)-3cp is the synthetic intermedi-
ate of (-)-paroxetine, whereas (R)-3xq serves as that of a
tachykinin antagonist developed by Glaxo Group Ltd., U.K.
Alkenylsilanes, 1p, 1t, and 1w, also underwent the enantiose-
lective addition across 2b under the Rh/chiral diene catalysis
to afford the corresponding 3-alkenylcyclohexanones of high
% ee (entries 7-9). In addition, even an unsubstituted vinyl
group was successfully installed by the use of vinylsilane 1y to
give 1,4-adduct 3yb in 94% ee (entry 10).5c,29 The success is
remarkable in view that conjugate addition of vinyl groups with
the corresponding vinylboronic acids often encounter the
problem of the reagent instability.23
Conclusion
In summary, we have demonstrated that organo[2-(hy-
droxymethyl)phenyl]dimethylsilanes serve as efficient reagents
for the rhodium-catalyzed 1,4-addition reactions. All the reac-
tions proceed with high chemoselectivity under mild conditions
in good yields using equimolar amounts of the silane reagents
in most cases. The ready accessibility and high stability toward
acid, base, and moisture of the present tetraorganosilicon
compounds as compared to conventional ones definitely present
the characteristic features of the silane reagents as an attractive
alternative to organoboron reagents. Other catalytic and non-
catalytic transformations of the silane reagents are currently
under investigations in our laboratory.
Reaction Mechanism. The catalytic cycle of the present
reaction should be initiated by the reaction of rhodium hydroxide
A with silane reagent 1 to give organorhodium intermediate B
(Scheme 1). Michael addition of R in B to an enone gives
rhodium enolate C,30 which acts as a base to react with 1 to
Acknowledgment. We highly acknowledge Prof. Michinori
Suginome and Dr. Toshimichi Ohmura (Kyoto University) for
kind assistance in chiral HPLC analysis. This work has been
supported financially by Grant-in-Aids for Creative Scientific
Research, No. 16GS0209, Scientific Research on Priority Areas
“Reaction Control of Dynamic Complex” and “Synergy of
Elements”, and COE Research on “United Approach to New
Material Science” from MEXT. This paper is dedicated to the
memory of the late Professor Emeritus Yoshihiko Ito.
(26) (a) Tokunaga, N.; Otomaru, Y.; Okamoto, K.; Ueyama, K.; Shintani, R.;
Hayashi, T. J. Am. Chem. Soc. 2004, 126, 13584. (b) Otomaru, Y.;
Okamoto, K.; Shintani, R.; Hayashi, T. J. Org. Chem. 2005, 70, 2503. (c)
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W.-L.; Hayashi, T. J. Am. Chem. Soc. 2006, 128, 5628.
(27) (a) Fischer, C.; Defieber, C.; Suzuki, T.; Carreira, E. M. J. Am. Chem.
Soc. 2004, 126, 1628. (b) Defieber, C.; Paquin, J.-F.; Serna, S.; Carreira,
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C. R. J.; Carreira, E. M. J. Am. Chem. Soc. 2005, 127, 10850. (d) Paquin,
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tallics 2005, 24, 2997. (f) Grundl, M. A.; Kennedy-Smith, J. J.; Trauner,
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(28) (a) Yu, M. S.; Lantos, I.; Peng, Z.-Q.; Yu, J.; Cacchio, T. Tetrahedron
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(29) The use of potassium vinylfluoroborate has been reported: (a) Pucheault,
M.; Darses, S.; Geneˆt, J.-P. Eur. J. Org. Chem. 2002, 3552. (b) Duursma,
A.; Boiteau, J.-G.; Lefort, L.; Boogers, J. A. F.; de Vries, A. H. M.; de
Vries, J. G.; Minnaard, A. J.; Feringa, B. L. J. Org. Chem. 2004, 69, 8045.
(30) Hayashi, T.; Takahashi, M.; Takaya, Y.; Ogasawara, M. J. Am. Chem. Soc.
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Supporting Information Available: Detailed experimental
procedures including spectroscopic and analytical data. This
material is available free of charge via the Internet at
http://pubs.acs.org.
JA071969R
(31) The absolute configuration has been determined based on the optical rotation
compared with that of authentic (S)-1z, [R]20 -52.6 (c 0.98, CHCl3),
D
synthesized from commercially available (S)-2-bromo-R-methylbenzyl
alcohol.
(32) For related mechanism of the transmetalation of arylboronic acids to
rhodium(I) via rhodium arylboronate, see: Zhao, P.; Incarvito, C. D.;
Hartwig, J. F. J. Am. Chem. Soc. 2007, 129, 1876.
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