Construction of Chiral Tetraorganosilicons by Tandem Desymmetrization of Silacyclobutanes/Intermolecular Dehydrogenative Silylation

Article abstract of DOI:10.1002/anie.201609022

We report a method to construct chiral tetraorganosilicons by tandem silacyclobutane (SCB) desymmetrization–dehydrogenative silylations. A wide array of dibenzosiloles with stereogenic quaternary silicon centers were obtained in good yields and enantioselectivities up to 93 % ee. Chiral TMS-segphos was found to be a superior ligand in terms of reactivity and enantioselectivity.

Full text of DOI:10.1002/anie.201609022

Angewandte
Communications
Chemie
International Edition: DOI: 10.1002/anie.201609022
German Edition: DOI: 10.1002/ange.201609022
Asymmetric Catalysis
Construction of Chiral Tetraorganosilicons by Tandem
Desymmetrization of Silacyclobutanes/Intermolecular
Dehydrogenative Silylation
Qing-Wei Zhang+, Kun An+, Li-Chuan Liu, Qi Zhang, Huifang Guo, and Wei He*
Abstract: We report a method to construct chiral tetraorgano-
silicons by tandem silacyclobutane (SCB) desymmetrization–
dehydrogenative silylations. A wide array of dibenzosiloles
with stereogenic quaternary silicon centers were obtained in
good yields and enantioselectivities up to 93% ee. Chiral TMS-
segphos was found to be a superior ligand in terms of reactivity
and enantioselectivity.
intramolecular dehydrogenative silylation reactions between
À
À
Si H and C H have also been reported, with some intriguing
mechanistic aspects unveiled very recently.[13] Other desym-
metrization reactions that did not involve silicon atom in the
bond formation, such as the [2+2+2] cycloaddition,[14] C H
À
bond activation,[15] and b-elimination of silacyclopentene
oxides,[16] were also developed.
[17]
À
The advent of catalytic activation of inert Si C bonds
Organosilicon compounds have found wide applications in
provides a conceptually new strategy to access stereogenic
functional materials and pharmaceuticals.[1] Construction of
silicon stereogenic centers has been a long-sought topic and is
currently underdeveloped compared to chiral carbon cen-
ters.[2–4] A significant challenge in controlling the chirality of
silicon resides in its tendency to form penta-covalent inter-
mediates. While such intermediates can often lead to
racemization via Berry pseudorotation,[5] they have also
been cleverly exploited to construct silicon stereogenic
centers via nucleophilic substitution by stoichiometric chiral
reagents.[4]
silicon from Si C precursors. Rh- or Ni-catalyzed desymmet-
À
rization of Si-aryl,[18] Si-alkynyl,[19] and Si-methyl bonds[20]
were developed recently. Shintani, Hayashi, and co-workers
have reported intriguing Pd-catalyzed desymmetric cyclo-
additions between silacyclobutane (SCB) and alkynes in both
intra- and intermolecular fashions (Scheme 1a).[21] Herein,
Aside from the different bonding behavior of silicon, the
general lack of strategies to construct silicon stereogenic
centers could be understood by the fact that chiral carbon
centers are often accessed by asymmetric addition to sp2-
hybridized carbons, whereas sp2-hybridized silicons are not
stable.[6] This simple fact has a very clear conceptual
consequence: stereogenic silicons must come from tetrasub-
stituted silicon precursors. It is therefore not surprising that
the catalytic construction of chiral silicons exclusively
depends on desymmetrization of prochiral silicons. In this
context, a number of prochiral silicons have been explored.
Dihydrosilanes are the most common precursors owing to
their versatile reactivity and wide availability. Desymmetri-
zation based on the signature hydrosilylation reaction of
alkynes,[7] ketones,[8] and alkenes[9] has been reported. Car-
bene insertion[10] and alcoholysis[11] are also very efficient and
highly enantioselective. The more challenging cross-coupling
reaction with aryl iodide has been described.[12] Asymmetric
Scheme 1. Desymmetrization of SCB.
construction of chiral tetraorganosilicons via Rh-catalyzed
tandem SCB desymmetrization/C H silylation and intermo-
À
lecular dehydrogenative silylation processes is reported
(Scheme 1b).[22] This method produced a wide array of
dibenzosiloles with silicon stereogenic centers in good yield
and high enantioselectivity. Of note, benzosiloles have been
extensively studied owing to their promising optoelectronic
properties.[1] However, to our knowledge, only three exam-
ples have been reported for the synthesis of dibenzosiloles
with silicon stereogenic centers.[13–15]
[*] Dr. Q.-W. Zhang,[+] K. An,[+] L.-C. Liu, Q. Zhang, Dr. H. Guo,
Prof. Dr. W. He
We commenced our study by using SCB[23,24] 1a and 2-
chlorothiophene 2a as the model substrates under the
catalysis of Rh(cod)Cl (10 mol%) (Table 1). No reaction
took place in the absence of a ligand (entry 1). Because
School of Pharmaceutical Sciences, Tsinghua University
Beijing, 100084 (China)
E-mail: whe@mail.tsinghua.edu.cn
Homepage: http://www.sps.tsinghua.edu.cn/en/team/team/2016/
0814/45.html
À
[+] These authors contributed equally to this work.
a pronounced ligand effect on the C H silylation was
observed in our earlier work,[25] a panel of ligands were
screened (for ligand structures, see Figure S1 in the Support-
ing Information). When (S)-DTBM-BINAP was used, prod-
Supporting information and the ORCID identification number(s) for
the author(s) of this article can be found under
http://dx.doi.org/10.1002/anie.201609022.
Angew. Chem. Int. Ed. 2016, 55, 1 – 6
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1
These are not the final page numbers!

Angewandte
Communications
Chemie
Table 1: Optimization of the reaction parameters.[a]
arene partner 2 using SCB 1a (R = Me) and 1b (R = Cl). The
reaction between 2-chlorothiophene (2a) and 1a gave
dibenzosilole 3aa in 60% yield and 86% ee, while the
reaction between 2a and 1b afforded the desired product 3ba
in 63% yield and 93% ee. The silylation of 3-chlorothiophene
(2b) took place exclusively at the 5-position but not at the
competing 2-position, and the corresponding products 3ab
and 3bb were obtained in 64% and 78% yields, with 91% and
88% ee, respectively. The more electron-rich 2-methylthio-
phene 2c was also compatible with the reaction, producing
only one constitutional product 3ac in 65% yield. In this case,
the enantioselectivity was lower (78% ee). The reactions
involving 3-methylthiophene 2d were also very regioselective,
but the enantioselectivities varied significantly: 77% ee was
observed for 3ad and 92% ee was obtained for 3bd.
The less reactive benzene (1e) and 3, 5-difluorobenzene
(1 f) were then employed. Owing to the lower reactivity, they
were used as the solvent for the reaction (see footnote d). The
reaction between benzene with SCB 1a and 1b successfully
afford the desired products 3ae and 3be in a moderate yield
(54%). The enantioselectivities were lower, however, with
65% ee for 3ae and 68% ee for 3be. The absolute
configuration of 3ae was unambiguously determined to be S
by single-crystal X-ray spectroscopy.[27] 3,5-Difluorobenzene
1 f was slightly more reactive, and the reaction gave the
corresponding product 3af in a higher yield (63%) than that
of 3ae with similar enantioselectivity (67% ee).
A number of SCBs bearing different substituents on
ring B were then tested using 2-chlorothiophene 2a as the
arene partner. SCB 1c with an electron-withdrawing para-F
substituent reacted smoothly with 2a to give the product 3ca
in a good yield (70%) with a high enantioselectivity (91% ee).
The electron-donating para-methoxyl group in SCB 1d did
not show an adverse effect, furnishing the product 3da in
a 67% yield with 93% ee. SCBs 1e, 1 f, and 1g bearing meta-
substituents were also capable substrates. The reaction of
SCB 1e afforded the product 3ea in 61% yield and 88% ee,
while SCB 1 f gave the product 3 fa in an excellent enantio-
selectivity (90% ee). To test the limit of the reaction, SCB 1g
was reacted with the least active benzene 2e. The desired
product 3ge was obtained in a 69% yield and a good
enantioselectivity (80% ee). This method was successfully
extended to the synthesis of bis-silole 3ha, which was
obtained in a 54% combined yield (3ha : racemate = 11:1
by HPLC, for details see page 29 in the Supporting Informa-
tion) with 92% ee. When ring B of the substrate was changed
into a ferrocene unit, the reaction showed a very high
efficiency (88% yield). The desired product 3ie was isolated
as a single diastereomer in 91% ee.
Entry
Ligand
Yield [%][b]
ee [%][c]
1
2
3
4
5
6
7
8
–
–
43
<10
21
28
<10
19
25
35
<10
28
–
À64
À66
60
(S)-DTBM-BINAP
(S)-MeO-Biphep
(R)-DTBM-MeO-Biphep
(S)-TMS-MeO-Biphep
(R)-Segphos
(R)-DM-Segphos
(R)-DTBM-Segphos
(R)-TMS-Segphos
(S)-DTBM-C1-Tunephos
(R)-TMS-Segphos
(R)-TMS-Segphos
(R)-TMS-Segphos
(R)-TMS-Segphos
(S)-TMS-Segphos
À86
22
38
72
86
9
10
11[d]
12[e]
13[e,f]
14[f]
15[g]
À66
86
46, 44[h]
35
60
76
86, 85[h]
86
86
73
[a] Conditions: 1a (0.1 mmol), 2a (0.2 mmol) in p-xylene (1 mL) unless
otherwise noted, 408C for 24 hrs. [b] Isolated yield. [c] Determined by
HPLC. [d] In 1,4-dioxane. [e] In DCE. [f] [Rh(cod)OH] as the catalyst.
[g] Triethylsilane (10 mol%) was added. [h] 3 mmol scale.
uct 3aa was observed in 43% yield with excellent regiose-
lectivity and moderate enantioselectivity (64% ee, entry 2).
MeO-Biphep-type ligands, which possess narrower bite
angles compared with BINAP, were screened (entries 3–5).
Among this type of ligand, the reactivity improved as the
stereohindrance increased, with yields ranging from < 10% to
28%. The (S)-TMS-MeO-Biphep gave a high enantioselec-
tivity (À86% ee). Encouraged by these results, Segphos that
have even narrower bite angles were then examined
(entries 6–9). A similar correlation between the reactivity
and the ligand steric hindrance was again noted. With the (R)-
TMS-Segphos ligand, 86% ee was obtained, albeit with
a lower 35% yield (entry 9).[26] Further increasing the stereo-
hindrance by using (S)-DTBM-C1-Tunephos resulted in
a further decreased yield of < 10% (entry 10).
We then focused on optimizing the reaction using the (R)-
TMS-Segphos ligand. The solvent had a significant effect on
the yield, but not on the enantioselectivity. For example, the
reaction gave the same 86% ee in 1,4-dioxane and in
dichloroethane (DCE), but the yields were much higher in
DCE (entry 11 versus 12). When the reaction was carried out
on 3 mmol scale, product 3aa could also be obtained in
a comparable 44% yield and 85% ee. When [Rh(cod)OH]
was used as the catalyst instead of [Rh(cod)Cl], a 35% yield
was obtained for reaction in DCE (entry 13). Satisfyingly, the
yield was improved to 60% with p-xylene as the solvent
(entry 14). Disiloxane (see Scheme 2) and biphenyl side
products accounted for the mass balance. The disiloxane
can be effectively suppressed by adding triethylsilane at the
cost of the enantioselectivity (entry 15 and Supporting
Information).
The possible pathways of the current reaction are shown
in Scheme 2, which involve different sequences of bond
formation. In pathway a, the well-documented intermolecular
dehydrogenative silylation[22] between the arene and the Si H
À
À
happens first, followed by asymmetric intramolecular C H
silylation of SCB. At face value, the latter step is a close
analogue of the racemic reaction[25b] we reported recently (see
below). Pathway b entails an intramolecular dehydrogenative
silylation, which is also well established.[13] However, the
The substrate scope was demonstrated using the opti-
mized reaction conditions. We first examined the (hetero)-
À
intermolecular C H silylation of SCB is not known to date.
2
www.angewandte.org
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2016, 55, 1 – 6
These are not the final page numbers!

Angewandte
Communications
Chemie
reaction is not a simple asymmetric version of our earlier
report because the reaction did not proceed via the inter-
mediacy of A. This phenomena could be attributed to less
stereodifferentiation between methyl versus aryl groups, as
compared to H versus aryl group in the oxidative insertion
step.
Further control experiments were then performed to
distinguish pathways b and c (Scheme 4). First, reaction of
independently synthesized spirosilole 8 (intermediate B)
À
failed to give C H silylation product 9, while the desilylated
side product 10 was obtained in a 91% yield (Scheme 4a).
Scheme 2. Possible reaction pathways.
Pathway c requires that the SCB reacts prior to the commonly
À
known reactive Si H bond. A subsequent intermolecular
dehydrogenative silylation that proceeded in either a stereo-
specific or a stereoconvergent fashion is necessary for the
formation of the chiral product 3.
We attempted to isolate possible reaction intermediates
(for example, A, B, or C) in reaction mixtures that were
obtained by purposely stopping the reaction at low conver-
sions. Except for the product 3 and disiloxane D, no other
discernible compound was obtained. This observation is
consistent with our NMR studies, which showed no signals
corresponding to any of the proposed intermediates during
the progression of the reactions. Therefore, we performed
a number of control experiments to identify viable reaction
intermediates.
Control experiments related to pathway a are shown in
Scheme 3. Compound 4 (substrate 1c in our previous racemic
reaction[25b]) was converted to product 5 in a low yield (23%)
under the conditions of this work, compared to 84% under
previous conditions.[25b] However, almost no enantioselectiv-
Scheme 4. Control experiments on pathways b and c.
This experiment suggested that the final product 3 was not
formed via pathway b. However, given the observation that
biphenyl side products were observed in many of the
reactions reported in Table 2, it is likely that pathway b is
a counterproductive competing pathway.
Despite numerous attempts, we failed to isolate inter-
mediate C in the reaction of 1 in absence of the arene partner
2 even under stringent glovebox conditions. Therefore,
intermediate C (tertiary silane 11) was prepared in both
racemic and enantio-enriched forms. A series of control
reactions substantiated that the stereo-determining step is the
À
SCB opening/intramolecular C H silylation process in path-
way c (Scheme 4b). It is clear that the intermolecular
dehydrogenative coupling between 11 and 2a is stereospecific
and independent of the chirality of the ligand. Interestingly,
À
À
such types of stereospecific intermolecular Si H/C H dehy-
drogenative coupling is rarely reported.[13c]
In conclusion, we reported a method to construct
dibenzosiloles with silicon stereogenic centers, which hinged
À
on the newly discovered C H silylation reactivity of SCB. In
À
this reaction, SCB undergoes desymmetric C H silylation in
Scheme 3. Control experiments on pathway a.
À
the presence of a reactive Si H bond, producing a chiral
silane intermediate that ultimately furnished the dibenzo-
silole product. This works unveils a number of surprising
reactivity features that warrant further investigation.
ity was observed under both sets of conditions (6% and 3%
ee, Scheme 3a). Compound 6 was then synthesized and
subjected to the reaction conditions. In this case, no reaction
was observed and substrate 6 was recovered even after
extended heating at elevated temperature (808C) (Sche-
me 3b). These control experiments suggested that the present
Angew. Chem. Int. Ed. 2016, 55, 1 – 6
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
3
These are not the final page numbers!

Angewandte
Communications
Chemie
Table 2: Substrate scope.[a]
[3] a) F. S. Kipping, J. Chem. Soc. Trans. 1907, 91, 209; b) L. H.
Sommer, C. L. Frye, G. A. Parker, K. W. Michael, J. Am. Chem.
Soc. 1964, 86, 3271; c) R. Corriu, G. Royo, J. Organomet. Chem.
1968, 14, 291; d) D. Terunuma, K. Murakami, M. Kokubo, K.
Senda, H. Nohira, Bull. Chem. Soc. Jpn. 1980, 53, 789; e) K.
Yamamoto, Y. Kawanami, M. Miyazawa, J. Chem. Soc. Chem.
Commun. 1993, 436; f) Y. Kawakami, M. Omote, I. Imae, E.
Shirakawa, Macromolecules 2003, 36, 7461.
[4] a) W. J. Richter, J. Organomet. Chem. 1979, 169, 9; b) K.
Kobayashi, T. Kato, M. Unno, S. Masuda, Bull. Chem. Soc.
Jpn. 1997, 70, 1393; c) A. Kawachi, H. Maeda, K. Mitsudo, K.
Tamao, Organometallics 1999, 18, 4530; d) K. Tomooka, A.
Nakazaki, T. Nakai, J. Am. Chem. Soc. 2000, 122, 408; e) A.
Nakazaki, J. Usuki, K. Tomooka, Synlett 2008, 2064; f) N. Oka,
M. Nakamura, N. Soeda, T. Wada, J. Organomet. Chem. 2009,
694, 2171; g) J. O. Bauer, C. Strohmann, Angew. Chem. Int. Ed.
2014, 53, 720; Angew. Chem. 2014, 126, 738; h) J. O. Bauer, C.
Strohmann, J. Am. Chem. Soc. 2015, 137, 4304; i) K. Igawa, J.
Takada, T. Shimono, K. Tomooka, J. Am. Chem. Soc. 2008, 130,
16132.
[5] a) R. S. Berry, Rev. Mod. Phys. 1960, 32, 447; b) R. S. Berry, J.
Chem. Phys. 1960, 32, 933; c) E. P. A. Couzijn, J. C. Slootweg,
A. W. Ehlers, K. Lammertsma, J. Am. Chem. Soc. 2010, 132,
18127; d) C. Moberg, Angew. Chem. Int. Ed. 2011, 50, 10290;
Angew. Chem. 2011, 123, 10473.
[6] a) A. G. Brook, J. J. Gajewski, Heteroat. Chem. 1990, 1, 57;
b) V. V. Volkova, L. E. Guselꢀnikov, E. A. Volnina, E. N. Bur-
avtseva, Organometallics 1994, 13, 4661.
[7] K. Igawa, D. Yoshihiro, N. Ichikawa, N. Kokan, K. Tomooka,
Angew. Chem. Int. Ed. 2012, 51, 12745; Angew. Chem. 2012, 124,
12917.
[8] a) T. Hayashi, K. Yamamoto, M. Kumada, Tetrahedron Lett.
1974, 15, 331; b) R. J. P. Corriu, J. J. E. Moreau, J. Organomet.
Chem. 1974, 64, C51; c) T. Ohta, M. Ito, A. Tsuneto, H. Takaya,
J. Chem. Soc. Chem. Commun. 1994, 2525.
[a] Conditions: 1 (0.1 mmol), 2 (0.2 mmol, 0.4 mmol for 3ha) in p-xylene
(1 mL) at 408C; [b] Isolated yield. [c] Determined by HPLC. [d] neat ArH
(1 mL) instead of p-xylene. [e] (S)-TMS-segphos was used as ligand,
reversed configuration and ee were shown. [f] [Rh(cod)Cl] (10 mol%) as
the catalyst.
[9] Alkene: a) K. Tamao, K. Nakamura, H. Ishii, S. Yamaguchi, M.
Shiro, J. Am. Chem. Soc. 1996, 118, 12469; b) Y. Naganawa, T.
Namba, M. Kawagishi, H. Nishiyama, Chem. Eur. J. 2015, 21,
9319.
[10] Carbene insertion: Y. Yasutomi, H. Suematsu, T. Katsuki, J. Am.
Chem. Soc. 2010, 132, 4510.
[11] Alcoholysis: a) R. J. P. Corriu, J. J. E. Moreau, Tetrahedron Lett.
1973, 14, 4469; b) D. R. Schmidt, S. J. OꢀMalley, J. L. Leighton, J.
Am. Chem. Soc. 2003, 125, 1190.
Acknowledgements
We acknowledge financial support from NSFC (21371107,
21521091, 21625104), the China Postdoctoral Science Foun-
dation (2013M540083), and Tsinghua University Initiative
Scientific Research Program (20161080166).
[12] Arylation by Ar-I: Y. Kurihara, M. Nishikawa, Y. Yamanoi, H.
Nishihara, Chem. Commun. 2012, 48, 11564.
Keywords: dibenzosiloles · enantioselectivity ·
silacyclobutanes · tetraorganosilicons
[13] Intramolecular dehydrogenative coupling: a) Y. Kuninobu, K.
Yamauchi, N. Tamura, T. Seiki, K. Takai, Angew. Chem. Int. Ed.
2013, 52, 1520; Angew. Chem. 2013, 125, 1560; b) M. Murai, H.
Takeshima, H. Morita, Y. Kuninobu, K. Takai, J. Org. Chem.
2015, 80, 5407; c) M. Murai, Y. Takeuchi, K. Yamauchi, Y.
Kuninobu, K. Takai, Chem. Eur. J. 2016, 22, 6048.
[14] a) R. Shintani, C. Takagi, T. Ito, M. Naito, K. Nozaki, Angew.
Chem. Int. Ed. 2015, 54, 1616; Angew. Chem. 2015, 127, 1636;
b) R. Shintani, R. Takano, K. Nozaki, Chem. Sci. 2016, 7, 1205.
[15] R. Shintani, H. Otomo, K. Ota, T. Hayashi, J. Am. Chem. Soc.
2012, 134, 7305.
[1] For reviews see: a) S. Yamaguchi, K. Tamao, in Silicon-contain-
ing Polymers in The Science and Technology of their Synthesis
and Applications (Eds.: R. G. Jones, W. Ando, J. Chojnowski),
Kluwer Academic Publishers, Dordrecht, 2000, pp. 461 – 498;
b) J. Y. Corey in Advances in Organometallic Chemistry, Vol. 59
(Eds.: F. H. Anthony, J. F. Mark), Academic Press, New York,
2011, pp. 1 – 328.
[16] K. Igawa, D. Yoshihiro, Y. Abe, K. Tomooka, Angew. Chem. Int.
Ed. 2016, 55, 5814; Angew. Chem. 2016, 128, 5908.
[17] For selected recent examples see: a) Q. W. Zhang, K. An, W. He,
Angew. Chem. Int. Ed. 2014, 53, 5667; Angew. Chem. 2014, 126,
5773; b) Y. Liang, S. Zhang, Z. Xi, J. Am. Chem. Soc. 2011, 133,
9204; c) Y. Liang, W. Geng, J. Wei, Z. Xi, Angew. Chem. Int. Ed.
2012, 51, 1934; Angew. Chem. 2012, 124, 1970; d) M. Tobisu, M.
Onoe, Y. Kita, N. Chatani, J. Am. Chem. Soc. 2009, 131, 7506.
[2] a) M. A. Brook in Silicon in Organic, Organometallic, and
Polymer Chemistry, Wiley, New York, 2000, pp. 115 – 137; b) M.
Toshihiro, K. Kei, N. Norihiro, S. Yoshikazu, Curr. Org. Chem.
2002, 6, 1469; c) S. Rendler, G. Auer, M. Keller, M. Oestreich,
Adv. Synth. Catal. 2006, 348, 1171; d) R. Shintani, Asian J. Org.
Chem. 2015, 4, 510; e) J. O. Bauer, C. Strohmann, Eur. J. Inorg.
Chem. 2016, 2868.
4
www.angewandte.org
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2016, 55, 1 – 6
These are not the final page numbers!

Angewandte
Communications
Chemie
[18] a) R. Kumar, Y. Hoshimoto, H. Yabuki, M. Ohashi, S. Ogoshi, J.
Hirano, H. Yorimitsu, K. Oshima, J. Am. Chem. Soc. 2007, 129,
Am. Chem. Soc. 2015, 137, 11838; b) R. Shintani, E. E. Maciver,
F. Tamakuni, T. Hayashi, J. Am. Chem. Soc. 2012, 134, 16955.
[19] Si-Alkyne: R. Shintani, H. Kurata, K. Nozaki, Chem. Commun.
2015, 51, 11378.
[20] Si-Me: M. Onoe, K. Baba, Y. Kim, Y. Kita, M. Tobisu, N.
Chatani, J. Am. Chem. Soc. 2012, 134, 19477.
[21] a) R. Shintani, K. Moriya, T. Hayashi, J. Am. Chem. Soc. 2011,
133, 16440; b) R. Shintani, K. Moriya, T. Hayashi, Org. Lett.
2012, 14, 2902.
6094; c) K. Hirano, H. Yorimitsu, K. Oshima, Org. Lett. 2008, 10,
2199; d) N. Ishida, W. Ikemoto, M. Murakami, J. Am. Chem. Soc.
2014, 136, 5912; e) N. Agenet, J.-H. Mirebeau, M. Petit, R.
Thouvenot, V. Gandon, M. Malacria, C. Aubert, Organometal-
lics 2007, 26, 819.
[25] a) Q.-W. Zhang, K. An, L. C. Liu, Y. Yue, W. He, Angew. Chem.
Int. Ed. 2015, 54, 6918; Angew. Chem. 2015, 127, 7022; b) Q.-W.
Zhang, K. An, L. C. Liu, S. Guo, C. Jiang, H. Guo, W. He,
Angew. Chem. Int. Ed. 2016, 55, 6319; Angew. Chem. 2016, 128,
6427.
[26] C. S. Sevov, J. F. Hartwig, J. Am. Chem. Soc. 2014, 136, 10625.
[27] CCDC 1478459 (S)-3ae (flack parameter: À0.03 (4)) contains
the supplementary crystallographic data for this paper. These
data can be obtained free of charge from The Cambridge
Crystallographic Data Centre.
À
[22] For an up to date review on C H silylation see: C. Cheng, J. F.
Hartwig, Chem. Rev. 2015, 115, 8946.
[23] For reviews see: a) “1,1-Dimethylsilacyclobutane”: K. Hirano,
H. Yorimitsu, K. Oshima in Handbook of Reagents for Organic
Synthesis: Reagents for Silicon-Mediated Organic Synthesis (Eds.
P. L. Fuchs), Wiley, Hoboken, 2011, pp. 261 – 262; b) W.-X.
Zhang, S. Zhang, Z. Xi, Acc. Chem. Res. 2011, 44, 541; c) L.
Li, Y. Zhang, L. Gao, Z. Song, Tetrahedron Lett. 2015, 56, 1466;
d) N. V. Ushakov, F. Evgenii Sh, Russ. Chem. Rev. 2013, 82, 205.
[24] For selected recent examples see: a) J. Liu, X. Sun, M. Miyazaki,
L. Liu, C. Wang, Z. Xi, J. Org. Chem. 2007, 72, 3137; b) K.
Manuscript received: September 14, 2016
Final Article published: && &&, &&&&
Angew. Chem. Int. Ed. 2016, 55, 1 – 6
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
5
These are not the final page numbers!

Angewandte
Communications
Chemie
Communications
Asymmetric Catalysis
Q.-W. Zhang, K. An, L.-C. Liu, Q. Zhang,
H. Guo, W. He*
&&&& — &&&&
Construction of Chiral
Tetraorganosilicons by Tandem
Desymmetrization of Silacyclobutanes/
Intermolecular Dehydrogenative
Silylation
Chiral silicon: A Rh-catalyzed reaction
between silacyclobutane and (hetero)-
arenes in the presence of (R)- or (S)-TMS-
segphos provides access to a wide array
of chiral dibenzosiloles in good yields and
enantioselectivities (up to 93% ee). The
reaction proceeds through a rarely docu-
mented desymmetrization of silacyclo-
butane, followed by intra- and intermo-
lecular dehydrogenative silylation pro-
cesses.
6
www.angewandte.org
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2016, 55, 1 – 6
These are not the final page numbers!