Synthesis of functionalized benzylsilanes from arylzinc compounds and (iodomethyl)trimethylsilane by means of a novel Rh catalysis

Article abstract of DOI:10.1021/jo0520994

The catalytic activity of a Rh complex in cross-coupling between ArZnI and TMSCH₂l was examined in which the Rh complex, generated in situ from [RhCl(1,5-cyclooctadiene)]₂ and 1,1′-bis(diphenylphosphino)- ferrocene, exhibited excellent catalytic activity for the production of various functionalized benzylsilanes in good yields. From ³¹P NMR studies of various solutions containing several of the reaction components, confirmation of the rapid and quantitative transfer of aryl groups from ArZnI to the Rh complex to form arylrhodium species was ascertained. A catalytic cycle, commencing with the transmetalation, was thus proposed for the reaction.

Full text of DOI:10.1021/jo0520994

Synthesis of Functionalized Benzylsilanes from Arylzinc Compounds
and (Iodomethyl)trimethylsilane by Means of a Novel Rh Catalysis
Hideki Takahashi, Kabir M. Hossain, Yasushi Nishihara, Takanori Shibata, and
Kentaro Takagi*
Department of Chemistry, Faculty of Science, Okayama UniVersity, Tsushima, Okayama 700-8530, Japan
takagi@cc.okayama-u.ac.jp
ReceiVed October 7, 2005
The catalytic activity of a Rh complex in cross-coupling between ArZnI and TMSCH
which the Rh complex, generated in situ from [RhCl(1,5-cyclooctadiene)] and 1,1′-bis(diphenylphosphino)-
ferrocene, exhibited excellent catalytic activity for the production of various functionalized benzylsilanes
2
I was examined in
2
31
in good yields. From P NMR studies of various solutions containing several of the reaction components,
confirmation of the rapid and quantitative transfer of aryl groups from ArZnI to the Rh complex to form
arylrhodium species was ascertained. A catalytic cycle, commencing with the transmetalation, was thus
proposed for the reaction.
Introduction
Pd- or Ni-catalyzed cross-coupling of carbon electrophiles
been realized recently in other types of cross-coupling of R+
from carbonyl compounds or conjugated enones with arylme-
tallic compounds of B, Si, Bi, Ti, or Zn, where transmetalation
has been known to be an essential step in the catalytic cycle.5
From consideration of this phenomenon, it was envisaged that
certain reactions, hitherto unsatisfactory results with Pd or Ni
+
R from aryl, alkenyl, or alkynyl halides with organometallic
compounds of B, Si, Sn, Zn, and so on, is one of the most useful
methods for constructing carbon-carbon bonds in organic
1
synthesis. In contrast to the thoroughly investigated Pd or Ni
2
catalysis, may be affected by making use of a Rh catalyst when
catalysis, the catalytic activity of other transition metals,
+
3
R
and/or organometallic compounds are appropriate for the
including Rh, has been explored to a far less extent. The
reaction via path A. Among such reactions, the cross-coupling
of arylzinc compounds with silylmethyl halides attracted our
attention (Figure 2), as arylzinc compounds are prepared readily
peculiar nature of Rh-complex catalysis, from the context that
not only the common catalytic cycle commencing with oxidative
addition but also one commencing with transmetalation are
allowed, does deem it noteworthy (path A vs path B of Figure
6
from aryl iodides and zinc powder with 100% atom efficiency,
3
b,4
and of which some are known to form Rh-Ar complexes.7
Silylmethyl halides exhibit enhanced reactivity to Rh in oxida-
tive addition, probably through a nucleophilic displacement
1).
Furthermore, the excellent catalytic activity of Rh has
(
1) For review, see: (a) Metal-Catalyzed Cross-Coupling Reactions;
Diederich, F., Stang, P. J., Eds.; Wiley-VCH: Weinheim, Germany, 1998.
b) Handbook of Organopalladium Chemistry for Organic Synthesis;
(
Negishi, E., Ed.; John Wiley & Sons: New York, 2002. (c) Tsuji, J.
Palladium Reagents and Catalysis: InnoVation in Organic Synthesis; John
Wiley & Sons: New York, 1995.
(4) (a) Schwartz, J.; Hart, D. W.; Holden, J. L. J. Am. Chem. Soc. 1972,
94, 9269-9271. (b) Semmelhack, M. F.; Ryono, L. Tetrahedron Lett. 1973,
14, 2967-2970. (c) Hegedus, L. S.; Kendall, P. M.; Lo, S. M.; Sheats, J.
R. J. Am. Chem. Soc. 1975, 97, 5448-5452. (d) Fanizzi, F. P.; Sunley, G.
J.; Maitlis, P. M. J. Organomet. Chem. 1987, 330, C31-C32.
(5) For review, see: (a) Fagnou, K.; Lautens, M. Chem. ReV. 2003, 103,
169-196. (b) Hayashi, T.; Yamasaki, K. Chem. ReV. 2003, 103, 2829-
2844.
(6) For our synthesis of arylzinc compounds, see: (a) Takagi, K. Chem.
Lett. 1993, 469-472. (b) Ogawa, Y.; Saiga, A.; Mori, M.; Shibata, T.;
Takagi, K. J. Org. Chem. 2000, 65, 1031-1036. (c) Ikegami, R.; Koresawa,
A.; Shibata, T.; Takagi, K. J. Org. Chem. 2003, 68, 2195-2199. Except
for Zn, simple substances of other metals such as B, Si, Sn, Bi, or Ti are
not applicable to the synthesis of arylmetal compounds from aryl halides
as metallic sources.
(
2) For review, see: (a) Shinokubo, H.; Oshima, K. Eur. J. Org. Chem.
2
004, 2081-2091. (b) Beletskaya, I. P.; Cheprakov, A. V. Coord. Chem.
ReV. 2004, 248, 2337-2364. (c) Fuerstner, A.; Martin, R. Chem. Lett. 2005,
3
4, 624-629.
3) (a) Larock, R. C.; Hershberger, S. S. J. Organomet. Chem. 1982,
25, 31-41. (b) Larock, R. C.; Narayanan, K.; Hershberger, S. S. J. Org.
(
2
Chem. 1983, 48, 4377-4380. (c) Andrianome, M.; Delmond, B. J. Org.
Chem. 1988, 53, 542-545. (d) Andrianome, M.; Haberle, K.; Delmond, B.
Tetrahedron 1989, 45, 1079-1088. (e) Hossain, K. M.; Takagi, K. Chem.
Lett. 1999, 1241-1242. (f) Ueura, K.; Satoh, T.; Miura, M. Org. Lett. 2005,
7, 2229-2231. (g) Evans, P. A.; Uraguchi, D. J. Am. Chem. Soc. 2003,
125, 7158-7159. (h) Evans, P. A.; Leahy, D. K. J. Am. Chem. Soc. 2003,
125, 8974-8975.
(7) Krug, C.; Hartwig, J. F. J. Am. Chem. Soc. 2002, 124, 1674-1679.
1
0.1021/jo0520994 CCC: $33.50 © 2006 American Chemical Society
Published on Web 12/14/2005
J. Org. Chem. 2006, 71, 671-675
671

Takahashi et al.
FIGURE 1. Two catalytic cycles for transition-metal-catalyzed cross-coupling.
TABLE 1. Catalytic Synthesis of Benzylsilane 3aa
b
entry
catalyst
temp (°C)
yield (%)
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1:2 [RhCl(cod)]2/dppf
1:2 [RhCl(cod)]2/dppf
1:2 [RhCl(cod)]2/PPh3
1:2 [RhCl(cod)]2/ttmppc
40
rt
93
86
<5
13
67
59
20
37
<5
74
10
6
FIGURE 2. New entry in a synthetic method of functionalized
benzylsilanes.
40
40
40
40
40
40
rt
40
40
rt
1:2 [RhCl(cod)]2/P(t-Bu)3
mechanism,8,9 owing to the presence of a Si substituent at the
R position, and lack undesirable side reactions such as the â
elimination of the resulting oxidative adducts.
1:2 [RhCl(cod)]2/dtbpbd
1:2 [RhCl(cod)] /dppp
2
1:2 [RhCl(cod)]2/BINAP
RhCl(PPh3)3
e
f
0
1
2
3
4
1:2 [RhCl(cod)]2/dppf
1:2 [RhCl(cod)]2/dppf
Pd(PPh3)4
Results and Discussion
A reaction solution composed of phenylzinc iodide (1a; 1.2
equiv), (iodomethyl)trimethylsilane (2; 1.0 equiv), and a Rh
catalyst (5-10 mol %) in N,N,N′,N′-tetramethylurea (TMU) was
stirred at 40 °C for 6 h under nitrogen (Table 1). Throughout
this study, Rh catalysts were prepared in situ from [RhCl(cod)]2
Pd(dba)2/P(t-Bu)3
rt
rt
rt
<5
<5
<5
g
PdCl2(PhCN)2/dppf
15
NiBr2/dppfg
a
1
a (1.2 mmol), 2 (1.0 mmol), catalyst (0.05 mmol), and TMU (0.6
mL) were employed for all entries except entry 2, where 0.1 mmol of catalyst
was used. GLC yield. c ttmpp ) tris(2,4,6-trimethoxyphenyl)phosphine.
b
(cod ) 1,5-cyclooctadiene) and various phosphorus ligands
(Rh/P ) 1:2), among which Rh-dppf [dppf ) 1,1′-bis-
(diphenylphosphino)ferrocene] exhibited excellent catalytic
d
f
e
dtbpb ) 2-(di-tert-butylphosphino)biphenylg. DMF was used as solvent.
2
-Methoxyethyl ether was used as solvent. With Zn (0.2 mmol).
activity in the reaction, giving the desired coupling product 3a
in high yield (entry 1). Under the catalysis by Rh-dppf, the
reaction also took place smoothly at ambient temperature,
requiring 10 mol % of the catalyst (entry 2). Phosphorus ligands
such as P(t-Bu)3 and 2-(di-tert-butylphosphino)biphenyl gave
the reactive Rh catalyst, but the selectivity was inferior to that
of Rh-dppf, as biphenyl was produced in 31 and 40% yields,
respectively, along with the desired product (entries 5 and 6).
Other Rh catalysts, including the Wilkinson complex, were less
effective, and the desired reaction took place slowly, if at all
CO2R, COPh, CON(CH3)2, Cl, OCH3, N(C2H5)2, or CH2OAc
at the ortho, meta, or para position, 1b-m, underwent catalysis
by Rh-dppf in the reactions with 2 to afford the corresponding
coupling products 3b-m efficiently and in good to excellent
yields, as shown in Table 2. Heteroaromatic compound 1n was
also tolerated in the reaction (entry 13).
In principle, there exist four kinds of cross-coupling reactions
leading to benzylsilanes, with respect to the position of bond
formation, CH -Si or Ar-CH , and the formal electronic charge
2
2
+
-
-
+
(entries 3, 4, and 7-9). Moreover, neither Pd nor Ni complexes,
of coupling partners, for example, CH + Si or CH2 + Si
2
1
0-13
even ones containing dppf or P(t-Bu)3, showed catalytic activity
for this reaction (entries 12-15). As the reaction solvent, DMF
was also suitable (entry 10), but 2-methoxyethyl ether was less
effective than TMU (entry 11). (Chloromethyl)trimethylsilane
could not replace 2 under the examined conditions. Various
arylzinc compounds containing such functional groups as CN,
(Figure 3).
Among these, the present combination is the
1
3
least-studied one; therefore, the reaction reported herein
featuring a novel catalysis by Rh, the utility of readily available
starting materials 1 and 2, and a high degree of functional group
tolerance provides a novel and useful synthetic method for the
production of benzylsilanes, which are diversely employed as
valuable synthetic intermediates in organic synthesis.14
(8) Concerning the accelerating effect of R-silyl substituents on the
Next, the catalytic efficiency of Rh-dppf toward other alkyl
reactivity of alkyl electrophiles for nucleophilic substitution reactions, see
for example: (a) Oh, H. K.; Shin, C. H.; Lee, I. J. Chem. Soc., Perkin
Trans. 2 1993, 2411-2414. (b) Apeloig, Y.; Biton, R.; Abu-Freih, A. J.
Am. Chem. Soc. 1993, 115, 2522-2523.
1
5
halides such as tributyl(iodomethyl)stannane (4) or 3-iodo-
2,2-dimethylpropane (5) was examined. Though both bear a
structural resemblance to 2 with respect to the lack of a
(9) Concerning the SN2 mechanism for oxidative addition of alkyl
electrophiles to Rh(I), see for example: (a) Chauby, V.; Daran, J.-C.; Serra-
Le Berre, C.; Malbosc, F.; Kalck, P.; Gonzalez, O. D.; Haslam, C. E.;
Haynes, A. Inorg. Chem. 2002, 41, 3280-3290. (b) Ellis, P. R.; Pearson,
J. M.; Haynes, A.; Adams, H.; Bailey, N. A.; Maitlis, P. M. Organometallics
(10) K: (a) Corriu, R. J. P.; Guerin, C. J. Chem. Soc., Chem. Commun.
1980, 168-169. Li: (b) Sekiguchi, A.; Nanjo, M.; Kabuto, C.; Sakurai, H.
Organometallics 1995, 14, 2630-2632. Si/Pd: (c) Eaborn, C.; Griffiths,
R. W.; Pidcock, A. J. Organomet. Chem. 1982, 225, 331-341.
1
994, 13, 3215-3226.
672 J. Org. Chem., Vol. 71, No. 2, 2006

Synthesis of Functionalized Benzylsilanes
â-hydrogen, their reactivity toward 1 was not necessarily similar
to that of 2, where the former afforded the desired products in
moderate to good yields,16 but the latter did not participate in
any reactions (Scheme 1). Furthermore, iodoethane gave the
protodezincation product of 1b selectively under similar condi-
tions. These results suggest that the presence of metallic
substituents at the R carbon of the alkyl halides is beneficial
for the Rh-dppf catalyzed cross-coupling of the halides with
8
,9,17
1.
During the course of this study, we observed that the reddish
brown color of Rh-dppf in TMU rapidly changed to dark green
when 1, for example 1b, was added to the solution, which
possibly indicates transmetalation between Rh-dppf and 1. To
(
11) Li: (a) Hultzsch, K. C.; Bonitatebus, P. J.; Jernelius, J.; Schrock,
R. R.; Hoveyda, A. H. Organometallics 2001, 20, 4705-4712. (b) Kyushin,
S.; Ikarugi, M.; Tsunakawa, S.; Izumi, Y.; Miyake, M.; Sato, M.;
Matsumoto, H.; Goto, M. J. Organomet. Chem. 1994, 473, 19-27. (c)
Kanda, T.; Kato, S.; Sugino, T.; Kambe, N.; Sonoda, N. J. Organomet.
Chem. 1994, 473, 71-83. (d) Engelhardt, L. M.; Leung, W. P.; Raston, C.
L.; Salem, G.; Twiss, P.; White, A. H. J. Chem. Soc., Dalton Trans. 1988,
31
gain accurate knowledge on the reaction, a preliminary P NMR
study was attempted using various solutions containing several
of the reaction components prepared at room temperature (Figure
18
31
4
). Initially, the P NMR of Rh-dppf, [RhCl(cod)]2 and dppf,
2
403-2409. (e) Carpenter, T. A.; Evans, G. E.; Leeper, F. J.; Staunton, J.;
in TMU/CH3CN-d3 was measured to reveal that the Rh-dppf
is composed of several species in the solution, including [RhCl-
(dppf)]2 as a major component. The subsequent addition of
Wilkinson, M. R. J. Chem. Soc., Perkin Trans. 1 1984, 1043-1051. (f)
Musker, W. K.; Scholl, R. L. J. Organomet. Chem. 1971, 27, 37-43. Mg:
1
9
(
2
g) Allen, J. M.; Aprahamian, S. L.; Sans, E. A.; Shechter, H. J. Org. Chem.
002, 67, 3561-3574. (h) De Boer, H. J. R.; Akkerman, O. S.; Bickelhaupt,
1
1
.0 equiv of 1b to the solution of Rh-dppf to give Rh-dppf-
F. J. Organomet. Chem. 1987, 321, 291-306. (i) Coughlin, D. J.; Salomon,
3
1
b afforded the completely different P NMR spectrum from
R. G. J. Org. Chem. 1979, 44, 3784-3790.
(12) Al/Pd: (a) Saulnier, M. G.; Kadow, J. F.; Tun, M. M.; Langley, D.
that of Rh-dppf, which was too complex to assign. Fortunately,
R.; Vyas, D. M. J. Am. Chem. Soc. 1989, 111, 8320-8321. B/Pd: (b)
Molander, G. A.; Yun, C.-S.; Ribagorda, M.; Biolatto, B. J. Org. Chem.
003, 68, 5534-5539. (c) Zou, G.; Reddy, Y. K.; Falck, J. R. Tetrahedron
31
the P NMR spectrum of Rh-dppf-1b in the copresence of
1
.0 equiv of PPh3 to give Rh-dppf-PPh3-1b in TMU/CH3-
2
2
1
22
Lett. 2001, 42, 7213-7215. (d) Soderquist, J. A.; Santiago, B.; Rivera, I.
Tetrahedron Lett. 1990, 31, 4981-4984. Cu: (e) Lappert, M. F.; Pearce,
R. J. Chem. Soc., Chem. Commun. 1973, 24-25. In/Pd: (f) Perez, I.; Sestelo,
J. P.; Sarandeses, L. A. J. Am. Chem. Soc. 2001, 123, 4155-4160. Mg/Ni:
CN-d3 or Rh-dppf-1b in DMSO-d6 showed the doublet
of triplets or the doublet of doublet signals with JRh-P ) 121
or 124 Hz, respectively, in accord with the formation of a Rh-
Ar bond. Simultaneously, the signals of Rh-dppf disappeared
completely. Alternatively, the addition of 20 equiv of 2 to the
TMU/CH3CN-d3 solution of Rh-dppf at 40 °C, in contrast, did
23
(
g) Organ, M. G.; Murray, A. P. J. Org. Chem. 1997, 62, 1523-1526. (h)
Brondani, D. J.; Corriu, R. J. P.; El Ayoubi, S.; Moreau, J. J. E.; Man, M.
W. C. Tetrahedron Lett. 1993, 34, 2111-2114. (i) Sengupta, S.; Leite, M.;
Raslan, D. S.; Quesnelle, C.; Snieckus, V. J. Org. Chem. 1992, 57, 4066-
31
not change the P NMR spectrum from that of Rh-dppf. These
results suggest that the reaction of 1 with Rh-dppf takes place
quantitatively at room temperature with only a stoichiometric
amount of 1, while the reaction of 2 with Rh-dppf, even at 40
4
068. (j) Kitching, W.; Olszowy, H. A.; Schott, I.; Adcock, W.; Cox, D. P.
J. Organomet. Chem. 1986, 310, 269-284. (k) Tamao, K.; Ishida, N.;
Kumada, M. J. Org. Chem. 1983, 48, 2120-2122. (l) Hayashi, T.; Katsuro,
Y.; Okamoto, Y.; Kumada, M. Tetrahedron Lett. 1981, 22, 4449-4452.
(
m) Tamao, K.; Sumitani, K.; Kiso, Y.; Zembayashi, M.; Fujioka, A.;
°
C with an excess amount of 2, does not.
Kodama, S.; Nakajima, I.; Minato, A.; Kumada, M. Bull. Chem. Soc. Jpn.
976, 49, 1958-1969. Mg/Pd: (n) Negishi, E.; Luo, F.-T.; Rand, C. L.
1
Therefore, under catalytic conditions (Rh-dppf/1/2 ) 0.05-
.1:1:1 from room temperature to 40 °C), the former reaction
Tetrahedron Lett. 1982, 23, 27-30. Sn/Pd: (o) Itami, K.; Mineno, M.;
Kamei, T.; Yoshida, J. Org. Lett. 2002, 4, 3635-3638. (p) Itami, K.; Kamei,
T.; Yoshida, J. J. Am. Chem. Soc. 2001, 123, 8773-8779. Zn/Pd: (q)
Abarbri, M.; Parrain, J.-L.; Kitamura, M.; Noyori, R.; Duchene, A. J. Org.
Chem. 2000, 65, 7475-7478. Reference 12k.
0
must overwhelmingly precede the latter reaction. Thus, the Rh-
Ar species generated possess higher reactivity toward 2 in an
4c
SN-type oxidative addition compared with that of Rh-dppf,
(
13) Cu: Majetich, G.; Leigh, A. J. Tetrahedron Lett. 1991, 32, 609-
10. Mg/Cu: Reference 11g.
14) Concerning the utility of 3 as the synthetic equivalent of benzyl
anions, see for example: (a) Chan, T. H.; Pellon, P. J. Am. Chem. Soc.
989, 111, 8737-8738. (b) Askari, S.; Lee, S.; Perkins, R. R.; Scheffer, J.
which probably enables the alkyl substrates, 2, which are
inactive coupling partners in path B, to be incorporated into
the catalytic reaction taking path A (Figure 1).
6
(
1
R. Can. J. Chem. 1985, 63, 3526-3529. (c) Aono, M.; Terao, Y.; Achiwa,
K. Chem. Lett. 1985, 339-340. (d) Kanemasa, S.; Tanaka, J.; Nagahama,
H.; Tsuge, O. Chem. Lett. 1985, 1223-1226. (e) Bennetau, B.; Dunogues,
J. Tetrahedron Lett. 1983, 24, 4217-4218. (f) Ito, Y.; Nakatsuka, M.;
Saegusa, T. J. Am. Chem. Soc. 1982, 104, 7609-7622. Reference 12p.
Concerning the utility of 3 as the precursor of benzyl alcohols, benzalde-
hydes, bibenzyls, or 4-alkylidenecyclohexenes, see for example: (g)
Cermenati, L.; Fagnoni, M.; Albini, A. Can. J. Chem. 2003, 81, 560-566.
In conclusion, the synthesis of benzylsilanes from the hitherto
least employed combination of coupling partners, ArM + XCH2-
(17) Nevertheless, both halides 2 and 4 are less reactive than iodomethane
3
e
as a coupling partner with 1 under the catalysis by Rh-dppf.
(18) 31P NMR spectra are summarized in Supporting Information.
(19) Major signals that appeared at δ 52.2 (d, JRh-P ) 202 Hz) could be
assigned to [RhCl(dppf)]2. The numerical value is close to that of [RhCl-
(
h) Hirao, T.; Morimoto, C.; Takada, T.; Sakurai, H. Tetrahedron 2001,
20
5
3
2
7, 5073-5079. (i) Fujii, T.; Hirao, T.; Ohshiro, Y. Tetrahedron Lett. 1993,
4, 5601-5604. (j) Yoshida, J.; Murata, T.; Isoe, S. Tetrahedron Lett. 1986,
7, 3373-3376. References 11i and 12k.
(P(i-Pr)3)2]2 δ 60.64 (d, JRh-P ) 197.2 Hz) or of [RhCl((S)-binap)]2 δ
23
49.7 (d, JRh-P ) 197 Hz). The second signals that appeared at δ 52.4
(dd, JRh-P ) 182 Hz) and δ 47.2 (dd, JRh-P ) 182 Hz, JP-P ) 43 Hz)
could be tentatively assigned to RhCl(L)(dppf), L ) cod or solvent, where
the former is partly overlapped with the major ones.
(
15) Seyferth, D.; Andrews, S. B. J. Organomet. Chem. 1971, 30, 151-
1
66.
16) Three kinds of cross-couplings have been applied to the synthesis
(
(20) Binger, P.; Haas, J.; Glasser, G.; Goddard, R.; Krueger, C. Chem.
Ber. 1994, 127, 1927-1929.
of benzylstannanes, ArCH2Sn. For the combination of ArCH2M (M ) Li,
Mg, or Zn) + XSn, see for example: (a) Labadie, J. W.; Stille, J. K. J.
Am. Chem. Soc. 1983, 105, 6129-6137. (b) Berk, S. C.; Yeh, M. C. P.;
Jeong, N.; Knochel, P. Organometallics 1990, 9, 3053-3064. (c) Marton,
D.; Russo, U.; Stivanello, D.; Tagliavini, G.; Ganis, P.; Valle, G. C.
Organometallics 1996, 15, 1645-1650. (d) Zhu, X.; Blough, B. E.; Carroll,
F. I. Tetrahedron Lett. 2000, 41, 9219-9222. For the combination of SnM
(21) The major signals that appeared at δ 43.3 (ddd, JP-P ) 308 Hz,
JRh-P ) 177 Hz, JP-P ) 31.7 Hz), 34.4 (dt, JRh-P ) 121 Hz, JP-P ) 33.1
Hz), and 27.5 (ddd, JP-P ) 308 Hz, JRh-P ) 173 Hz, JP-P ) 34.8 Hz)
could be assigned to RhAr(PPh3)(dppf). The numerical value is similar to
that of RhPh(PPh3)[(S)-binap] δ 35.4 (ddd, JRh-P ) 121 Hz, JP-P ) 39 Hz,
JP-P ) 30 Hz), 32.8 (ddd, JP-P ) 375 Hz, JRh-P ) 144 Hz, JP-P ) 43 Hz),
2
3
(
M ) K, Li, or Sn/Pd) + XCH2Ar, see: (e) Corriu, R. J. P.; Guerin, C. J.
and 29.6 (ddd, JP-P ) 375 Hz, JRh-P ) 143 Hz, JP-P ) 36 Hz).
Organomet. Chem. 1980, 197, C19-C21. (f) Tius, M. A.; Gomez-Galeno,
J. Tetrahedron Lett. 1986, 27, 2571-2574. (g) Azarian, D.; Dua, S. S.;
Eaborn, C.; Walton, D. R. M. J. Organomet. Chem. 1976, 117, C55-C57.
Reference 16a. For the combination of SnCH2M (M ) Mg/Ni or Zn/Pd) +
XAr, see: (h) Sato, T.; Kawase, A.; Hirose, T. Synlett 1992, 891-892.
Reference 12j. However, to our knowledge, the combination of ArM +
XCH2Sn has not been applied to the synthesis yet.
(22) The major signals that appeared at δ 42.3 (dd, JRh-P ) 183 Hz,
JP-P ) 29 Hz) and δ 30.2 (dd, JRh-P ) 124 Hz, JP-P ) 29 Hz) could be
tentatively assigned to RhAr(L)(dppf), L ) cod or solvent. For DMSO as
a ligand for Rh, see for example: Dorta, R.; Rozenberg, H.; Shimon, L. J.
W.; Milstein, D. Chem.sEur. J. 2003, 9, 5237-5249.
(23) Hayashi, T.; Takahashi, M.; Takaya, Y.; Ogasawara, M. J. Am.
Chem. Soc. 2002, 124, 5052-5058.
J. Org. Chem, Vol. 71, No. 2, 2006 673

Takahashi et al.
TABLE 2. Synthesis of Functionalized Benzylsilanesa
a
1
b-n (0.44 mmol), 2 (0.4 mmol), and TMU (0.25 mL) were employed in all entries. In entries 1, 3, 4, 6, and 7, 0.01 mmol of [RhCl(cod)]2 and 0.02
mmol of dppf were used, whereas 0.02 mmol of [RhCl(cod)]2 and 0.04 mmol of dppf were used in entries 2, 5, and 8-13. The reaction time was 12 h for
entries 1, 4, 9, and 12, 6 h for entries 3, 5-7, 10, 11, and 13, 24 h for entry 2, and 72 h for entry 8. b Isolated yield.
Si, has been accomplished, taking advantage of the novel
catalytic nature of the Rh complex. Characteristics of the
reaction such as the utility of readily available starting materials,
the great degree of functional group tolerance, and the simplicity
of the employed procedure make the reaction useful for
synthesizing benzylsilanes as valuable intermediates in organic
synthesis.
Experimental Section
All reactions were performed under an atmosphere of nitrogen
in oven-dried glassware. TMU was distilled under nitrogen and
stored over 4-Å molecular sieves. Phenyl(4-iodophenyl)metha-
2
4
24
none, phenyl(2-iodophenyl)methanone, (4-iodophenyl)methyl
acetate,25 (2-iodophenyl)methyl acetate, N,N-diethyl-4-iodoben-
25
FIGURE 3. Cross-coupling routes to 3.
674 J. Org. Chem., Vol. 71, No. 2, 2006

Synthesis of Functionalized Benzylsilanes
N,N-Dimethyl-4-[(trimethylsilyl)methyl]benzamide (3d): oil;
-
1 1
IR (neat) 1638, 1392, 1249, 853 cm ; H NMR δ -0.04 (s, 9H),
2
(
.08 (s, 2H), 2.98 (s, 3H), 3.04 (s, 3H), 6.98 (d, J ) 8.0 Hz), 7.26
d, J ) 8.0 Hz); 13C NMR δ -2.1, 27.2, 35.3, 39.6, 127.1, 127.6,
131.6, 142.5, 172.0; HRMS calcd for C13
H21NOSi, 235.1392; found,
+
2
35.1400 (M ).
Methyl 3-[(Trimethylsilyl)methyl]benzoate (3e): oil; IR (neat)
-
1 1
1
3
7
5
725, 1284, 851 cm ; H NMR δ -0.01 (s, 9H), 2.13 (s, 2H),
.89 (s, 2H), 7.19 (d, J ) 7.5 Hz, 1H), 7.28 (t, J ) 7.5 Hz, 1H),
.68 (s, 1H), 7.75 (d, J ) 7.5 Hz, 1H); 13C NMR δ -2.0, 26.9,
2.0, 125.2, 128.1, 128.9, 129.9, 132.5, 140.9, 167.4; HRMS calcd
+
for C12
H18SiO
2
, 222.1076; found, 222.1079 (M ).
4
-[(Trimethylsilyl)methyl]phenyl Acetate (3f): oil; IR (neat)
-
1
1
1
2
7
1
2
744, 1249, 1021, 851 cm ; H NMR δ 0.00 (s, 9H), 2.09 (s,
H), 2.09 (s, 3H), 5.06 (s, 2H), 7.00 (d, J ) 7.8 Hz), 7.22 (d, J )
.8 Hz); 13C NMR δ -2.0, 21.0, 26.8, 66.3, 128.1, 128.3, 131.2,
40.7, 170.9; HRMS calcd for C13
36.1234 (M ).
H
20
2
O Si, 236.1233; found,
+
N,N-Diethyl-4-[(trimethylsilyl)methyl]benzenamine (3g): oil;
-
1 1
IR (neat) 1615, 1518, 1263, 845 cm ; H NMR δ 0.02 (s, 9H),
1
6
.16 (t, J ) 7.2 Hz, 3H), 1.98 (s, 2H), 3.32 (q, J ) 7.2 Hz, 2H),
13
.64 (d, J ) 8.7 Hz, 2H), 6.88 (d, J ) 8.7 Hz, 2H); C NMR δ
1.9, 12.6, 25.2, 44.5, 112.9, 127.5, 128.8, 144.9; HRMS calcd
-
+
for C14
Phenyl{2-[(trimethylsilyl)methyl]phenyl}methanone (3j): oil;
H25NSi, 235.1756; found, 235.1759 (M ).
FIGURE 4. 31P NMR of Rh-phosphine complexes.
-
1 1
IR (neat) 1663, 1265, 849, 702 cm ; H NMR δ -0.05 (s, 9H),
.35 (s, 2H), 7.12-7.16 (m, 2H), 7.30-7.36 (m, 2H), 7.42-7.47
m, 2H), 7.54-7.56 (m, 1H), 7.78-7.82 (m, 2H); 13C NMR δ -1.1,
2
(
SCHEME 1
2
1
2
4.5, 123.5, 123.5, 128.5, 130.2, 130.5, 131.5, 133.0, 136.6, 138.5,
41.3, 198.7; HRMS calcd for C17
68.1285 (M ).
H20OSi, 268.1283; found,
+
Ethyl 4-[(Tributylstannyl)methyl]benzoate (7b): oil; IR (neat)
-
1
1
1
1
4
8
717, 1276, 1106, 772 cm ; H NMR δ 0.79-0.91 (m, 15H),
.20-1.32 (m, 6H), 1.36-1.48 (m, 9H), 2.37 (t, J ) 28.2 Hz, 2H),
.34 (q, J ) 7.2 Hz, 6H), 7.01 (d, J ) 8.3 Hz, 2H), 7.85 (d, J )
.3 Hz, 2H); 13C δ 9.4, 13.7, 14.4, 19.3, 27.3, 28.9, 60.5, 124.9,
zenamine,26 2-iodobenzonitrile,24 and 415 were prepared following
the literature methods. Other compounds including Zn powder were
purchased from a commercial supplier and used without further
126.6, 129.7, 150.4, 166.9; HRMS calcd for C22
H
38
O
2
Sn, 454.1894;
+
found, 454.1873 (M ).
2-Chloro[(trimethylsilyl)methyl]benzene (3l):27 1H NMR δ
0.03 (s, 9H), 2.28 (s, 2H), 6.98-7.13 (m, 3H), 7.29 (d, J ) 7.8
Hz, 1H); C NMR δ -1.5, 24.3, 125.2, 126.3, 129.3, 129.7, 132.6,
3
purification. The NMR spectra were recorded in CDCl at 300 MHz
1
13
13
for H or 75.5 MHz for C with TMS or chloroform-d
1
as the
internal standard, respectively.
138.8.
Benzyltrimethylsilane (3a). See ref 28.28
Phenyl{4-[(trimethylsilyl)methyl]}methanone (3c). See ref
29.29
Preparation of Ethyl 4-[(Trimethylsilyl)methyl]benzoate
3b): Representative Procedure. To [RhCl(cod)] (6.2 mg, 0.013
(
2
mmol) and dppf (13.9 mg, 0.025 mmol) was added a TMU solution
of arylzinc iodide 1b (0.32 mL, 0.55 mmol) with stirring for 30
min at room temperature. (Iodomethyl)trimethylsilane (2; 0.074 mL,
4-Methoxy[(trimethylsilyl)methyl]benzene (3h). See ref 11j.
2-[(Trimethylsilyl)methyl]benzonitrile (3i). See ref 12b.
Methyl 2-[(trimethylsilyl)methyl]benzoate (3k). See ref 14e.
2-[(Trimethylsilyl)methyl]phenyl acetate (3m). See ref 12d.
0.5 mmol) was added to the solution and stirred for 12 h at 40 °C.
The resulting mixture was quenched by the addition of aqueous
HCl. The work up, extracting with ether, washing with aqueous
HCl, drying over MgSO , and evaporating the solvent, afforded a
4
3
0
2-[(Trimethylsilyl)methyl]thiophene (3n). See ref 30.
Benzyltributylstannane (7a). See ref 31.31
crude product, which was chromatographed on silica gel with a
hexane/ethyl acetate (10:1) eluent to afford 102.8 mg of 3b
Supporting Information Available: General procedure for the
1
synthesis of arylzinc compounds, Figures S3-S25 of H NMR or
-
1
1
(
87%): oil; IR (neat) 1717, 1278, 1108, 855 cm ; H NMR δ
13
C NMR spectra of compounds 3a-n, 7a, and 7b, and Figures
-
0.01 (s, 9H), 1.38 (t, J ) 7.0 Hz, 3H), 2.16 (s, 2H), 4.35 (q, J )
31
S26-S33 of P NMR spectra of Rh complexes. This material is
7
.0 Hz, 2H), 7.04 (d, J ) 8.3 Hz, 2H), 7.90 (d, J ) 8.3 Hz, 2H);
available free of charge via the Internet at http://pubs.acs.org.
1
3
C NMR δ -2.0, 14.3, 27.9, 60.6, 126.2, 127.8, 129.5, 146.6,
1
(
66.8; HRMS calcd for C13
M ).
H O
20 2
Si, 236.1233; found, 236.1236
JO0520994
+
(
27) Eaborn, C.; Parker, S. H. J. Chem. Soc. 1954, 939-941.
(28) Guijarro, D.; Mancheno, B.; Yus, M. Tetrahedron 1994, 50, 8551-
(
24) Klapars, A.; Buchwald, S. L. J. Am. Chem. Soc. 2002, 124, 14844-
8558.
1
1
4845.
(
677-1682.
(29) Fuerstner, A.; Seidel, G. Tetrahedron 1995, 51, 11165-11176.
25) Miles, J. A.; Grabiak, R. C.; Cummins, C. J. Org. Chem. 1982, 47,
(30) Tamao, K.; Kodama, S.; Nakajima, I.; Kumada, M.; Minato, A.;
Suzuki, K. Tetrahedron 1982, 38, 3347-3354.
(31) Soundararajan, N.; Plutz, M. S. Tetrahedron Lett. 1987, 28, 2813-
2816.
(26) Adimurthy, S.; Ramachandraiah, G.; Ghosh, P. K.; Bedekar, A. V.
Tetrahedron Lett. 2003, 44, 5099-5101.
J. Org. Chem, Vol. 71, No. 2, 2006 675