Stereoselective C-H Borylations of Cyclopropanes and Cyclobutanes with Silica-Supported Monophosphane-Ir Catalysts

Article abstract of DOI:10.1002/chem.201404362

Heteroatom-directed C-H borylation of cyclopropanes and cyclobutanes was achieved with silica-supported monophosphane-Ir catalysts. Borylation occurred at the C-H bonds located γ to the directing N or O atoms with exceptional cis stereoselectivity relativ

Full text of DOI:10.1002/chem.201404362

DOI: 10.1002/chem.201404362
Communication
&
Organic Synthesis
Stereoselective CÀH Borylations of Cyclopropanes and
Cyclobutanes with Silica-Supported Monophosphane–Ir Catalysts
Ryo Murakami, Kiyoshi Tsunoda, Tomohiro Iwai, and Masaya Sawamura*[a]
Abstract: Heteroatom-directed CÀH borylation of cyclo-
propanes and cyclobutanes was achieved with silica-sup-
ported monophosphane–Ir catalysts. Borylation occurred
at the CÀH bonds located g to the directing N or O atoms
with exceptional cis stereoselectivity relative to the direct-
ing groups. This protocol was applied to the borylation of
Figure 1. Silica-supported monophosphanes.
a tertiary CÀH bond of a ring-fused cyclopropane.
panes.[4,13] Applicability for borylation of a tertiary CÀH bond
Cyclopropanes and cyclobutanes, categorized as small-ring car-
bocycles, are common units in natural products, biologically
active compounds, and synthetic building blocks.[1,2] Recently,
transition-metal-catalyzed CÀH bond activation strategies were
developed as direct methods for functionalizing small-ring
frameworks, such as cyclopropanes and cyclobutanes.[3–6]
Among these reactions, CÀH borylation reactions are attractive
because borylated small-ring compounds can act as “handles”
for diverse molecular transformations.[7–11] Recently, Hartwig
and co-workers reported the trans-selective borylation of sub-
stituted cyclopropanes by using Ir–phenanthroline catalyst sys-
tems.[4] However, introduction of a boron atom with cis stereo-
chemistry relative to a substituent existing in small-ring sys-
tems is still difficult. Furthermore, CÀH borylation of cyclobu-
tane derivatives has not yet been achieved.
and cyclobutane systems and the effectiveness of carbonyl-re-
lated directing groups are new features of this heterogeneous
catalysis.
Initially, Ir and Rh catalyst systems based on various ligands
([M(cod)(OMe)]2, M=Ir or Rh, 2 mol% M; cod=1,5-cycloocta-
diene) were evaluated for catalytic activity toward the boryla-
tion of 2-cyclopropylpyridine (1a, 0.4 mmol) with bis(pinacola-
to)diboron (2, 0.2 mmol) in THF.[14] As a result, the Ir complex
coordinated with the commercially available silica-supported
caged trialkylphosphane Silica-SMAP showed the greatest turn-
over efficiency (258C, 15 h), giving cyclopropylboronate 3a
1
(150% based on 2 by H NMR spectroscopy, Scheme 1) along
A previous report from our laboratory described the directed
borylation of primary and secondary C(sp3)ÀH bonds of N-alky-
lated amides, ureas, and aminopyridines[10b] and 2-alkylpyridi-
nes[10c] catalyzed by Ir- or Rh-catalyst systems based on immo-
bilized monophosphane ligands, such as Silica-SMAP[12] and
Silica-TRIP[12] (Figure 1). This strategy allowed the borylation of
a cyclohexane ring substituted with a pyridine directing group
with trans stereoselectivity, but its applicability for small-ring
systems was not demonstrated.
Scheme 1. Silica-SMAP–Ir-catalyzed borylation of 1a.
with 2,3-bisborylation product 3a’ (6%, vide infra for details
on this compound) in total yields of over 100%, which indicat-
ed that the HBpin formed during catalytic turnover also
worked as a borylating reagent (theoretical maximum yield
based on B atom is 200%).[15] The CÀH borylation occurred
with exclusive regio- and stereoselectivity at the three-mem-
bered ring CÀH bond located g to the pyridine N atom in
favor of the cis configuration, which indicates N-to-Ir coordina-
tion leading to a five-membered iridacyclic reaction pathway.
The existence of an intramolecular NÀB interaction in the prod-
uct (3a) was indicated by 11B NMR spectroscopy in CDCl3.[16] Ar-
omatic CÀH borylation on the pyridine ring, benzylic CÀH bor-
ylation, and ring-opening of the cyclopropane were not ob-
served. No reaction occurred with the corresponding Rh cata-
lyst under identical reaction conditions.
The present report describes the heteroatom-directed CÀH
borylation reactions of cyclopropanes and cyclobutanes cata-
lyzed by silica-supported monophosphane–Ir systems. The re-
actions proceeded under mild conditions with exceptional cis
stereochemistry relative to the directing group, and thus com-
plement Hartwig’s trans-selective CÀH borylation of cyclopro-
[a] R. Murakami, K. Tsunoda, Dr. T. Iwai, Prof. Dr. M. Sawamura
Department of Chemistry, Faculty of Science
Hokkaido University
Sapporo 060-0810 (Japan)
E-mail: sawamura@sci.hokudai.ac.jp
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201404362.
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Table 1. Silica-SMAP–Ir-catalyzed CÀH borylation of cyclopropane deriva-
tives (1) with diboron (2).[a]
Entry
1[c]
Substrate 1
Product 3
T [8C] Yield[b] [%]
25
168[d] (150)
Scheme 2. Silica-SMAP–Ir-catalyzed bisborylation of 1a.
2[c]
25
25
108[e,f] (82)
164[d] (158)
When the Silica-SMAP-Ir-catalyzed reaction of 1a was con-
ducted with 2.5 equivalents of 2, a novel 1,2,3-trisubstituted
cyclopropane derivative (3a’) with all-cis configuration was ob-
tained selectively (Scheme 2).[17] Single-crystal X-ray diffraction
confirmed the stereochemistry and intramolecular NÀB coordi-
nation.[18]
3[c]
Homogeneous Ir catalyst systems with Ph-SMAP,[19] PPh3,
PMe3, PCy3, or PtBu3 as well as [Ir(cod)(OMe)]2 without exoge-
nous ligands induced much lower borylation activity (0–54%
yields of 3a, 2 mol% of Ir at 25 or 508C for 15 h),[14] which indi-
cated the importance of immobilization. The phenanthroline-
based ligand (2,9-Me2phen), which was the optimal ligand in
the Hartwig’s study for the trans-selective cyclopropane boryla-
tion,[4] caused borylation of the pyridine ring (C4- and C5-posi-
tions, 78 and 59%, respectively, at 508C),[14] but not at the cy-
clopropane ring.
4
1e (X=NMe)
1e (X=NMe)
1 f (X=O)
3e (X=NMe)
3e (X=NMe)
3 f (X=O)
25
80
40
70
148[g] (133)
82[g] (78)
98 (87)[i]
5[h]
6
7
1g (X=S)
3g (X=S)
156 (130)
8
30
137[g] (123)[j]
9
40
50
86[g] (61)
91[g] (80)
Various heteroarenes functioned as
a directing group
(Table 1, entries 1–7). Electron-donating (1b,c) or -withdrawing
(1d) substituents at the 5-position of 2-cyclopropylpyridine
had little effect on the effectiveness of the cyclopropane CÀH
borylation (entries 1–3).
10
[a] Conditions: 1 (0.4 mmol), 2 (0.2 mmol), [Ir(cod)(OMe)]2 (0.004 mmol Ir),
Silica-SMAP (0.004 mmol P), THF (2 mL), 15 h. [b] Yields based on 2 were
determined by 1H NMR spectroscopy. Isolated yields are in parentheses.
Yield in excess of 100% indicates that HBpin formed during catalytic turn-
over also worked as a borylating reagent (theoretical maximum yield is
200%). [c] THF (1 mL). [d] Bisborylation products 3’ were observed in the
crude mixture (entry 1, 6%; entry 3, 11%). [e] Diboron 2 remained in the
crude mixture. [f] A partial N–B interaction was indicated by 11B NMR
spectroscopy. [g] The C=N reduction product of 1 was observed in the
crude mixture (entry 4, 39%; entry 5, 68%; entry 8, 48%; entry 9, 17%;
entry 10, 26%). [h] 1e (10 mmol), 2 (5 mmol), [Ir(cod)(OMe)]2 (0.005 mmol
Ir), Silica-SMAP (0.005 mmol P), THF (5 mL), 808C, 15 h. [i] Isolated product
was contaminated with arylboronates (10%). [j] Isolated product was con-
taminated with regioisomers (8%).
Benzoannulated N-heteroaryls, such as benzoimidazole, ben-
zooxazole, and benzothiazole, were suitable directing groups,
showing exclusive diastereoselectivity (Table 1, entries 4–7). For
instance, reaction of 2-cyclopropyl-N-methylbenzoimidazole
(1e) proceeded smoothly at 258C to afford borylation product
3e in 133% isolated yield based on 2 (entry 4).[20] Gram-scale
borylation of 1e was possible by decreasing catalyst loading
to 0.1 mol% Ir at 808C (entry 5). Benzooxazole (in 1 f) also
functioned as a directing group, but C(sp2)ÀH borylations were
minor reaction paths (entry 6). 2-Cyclopropylbenzothiazole
(1g) reacted cleanly at 708C to provide cyclopropylboronate
3g as a sole product (entry 7). The 11B NMR spectra of 3e–g in-
dicated that their azole groups were not coordinated to the
boron atom.[16]
consistent with the report of Hartwig’s group describing suc-
cessful nondirected cyclopropane borylation.[4]
Effects of alkyl substituents on the cyclopropane ring are
shown in Table 1 (entries 8–10). Methyl-group substitution with
trans geometry in 1h and geminal dimethyl substitution in 1i
had little effect on either reaction effectiveness or diastereose-
lectivity. Interestingly, a tertiary CÀH bond on the cyclopropane
ring of 2-(7-bicyclo[4.1.0]heptyl)-1-methyl-1H-benzoimidazole
(1j) successfully participated in borylation under mild condi-
tions (508C, entry 10). The structure of 3j was confirmed by
single-crystal X-ray diffraction analysis (Figure 2).[18] This is the
first catalytic borylation of a tertiary CÀH bond. These experi-
mental results demonstrating good tolerance toward substitut-
ed cyclopropanes likely reflect the increased acidity of the
small-ring CÀH bonds with relatively high s-character, and are
Carbonyl-related functional groups also acted as directing
groups for cyclopropane CÀH borylation as shown in Table 2.
N-Methoxyimine derived from dicyclopropyl ketone (1k) react-
ed at 258C to give monoborylation product 3k selectively
(Table 2, entries 1 and 2). For N-methoxyimine (1l) derived
from an unsymmetrical ketone, only the E isomer was convert-
ed to the corresponding cyclopropylboronate (3l) while the Z
isomers remained intact (entries 3 and 4, respectively). N-Mesi-
tylimine 1m was more efficiently borylated by using Silica-TRIP
than using Silica-SMAP (entries 5 and 6, respectively). Again,
only the E isomers participated in the transformation. N,N-Dii-
sopropylamide 1n reacted at 808C using Silica-SMAP with ex-
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Table 3. Silica-SMAP–Ir-catalyzed CÀH borylation of cyclobutane deriva-
tives (4) with diboron (2).[a]
Entry
1[c]
Substrate 4
Product 5
T. [8C]
Yield[b] [%]
105 (85)[d]
25
2
3[g]
40
80
109[e] (99)[f]
96[e] (94)[f]
4
50
99 (94)[f]
Figure 2. Molecular structure of the tertiary alkylboronate 3j.
[a] Conditions: 4 (0.4 mmol), 2 (0.2 mmol), [Ir(cod)(OMe)]2 (0.004 mmol Ir),
ligand (0.004 mmol P), THF (2 mL), 15 h. [b] Yields based on 2 were deter-
mined by 1H NMR spectroscopy. Isolated yield is in parentheses. Yield in
excess of 100% indicates that HBpin also worked as a borylating reagent
(theoretical maximum yield is 200%). [c] In THF (1 mL). [d] Isolated 5a
was contaminated with traces of impurities. [e] The C=N reduction prod-
ucts of 4 were observed in the crude mixture (entry 2, 39%; entry 3,
21%). [f] Isolated products were contaminated with arylboronates
(entry 2, 6%; entry 3, 6%; entry 4, 20%). [g] 4b (10 mmol), 2 (5 mmol), [Ir-
(OMe)(cod)]2 (0.005 mmol Ir), Silica-SMAP (0.005 mmol P), THF (5 mL),
808C, 15 h.
Table 2. Ir-catalyzed CÀH borylation of cyclopropanes (1) with carbonyl-
related functional groups.[a]
Entry Substrate 1 Product 3
Ligand
T [8C] Yield[b] [%]
1
2
Silica-SMAP
Silica-TRIP
25
25
107 (66)
88
3
4
Silica-SMAP
Silica-TRIP
25
25
115[c] (64)
104[c]
5[d]
6[d]
Silica-SMAP 100
85[c,e]
The cyclopropyl and cyclobutyl boronates (3e and 5b, re-
spectively) obtained through CÀH borylation were used for
transformations as shown in Scheme 3. Cyclopropylboronate
3e underwent transformation to a trifluoroborate salt,[11a] one-
carbon-homologation/oxidation sequence,[21] and Pd-catalyzed
Suzuki–Miyaura coupling with aryl or alkenyl bromides.[11a,22]
The alkenylated cyclopropane 8d is structurally related to
chrysanthemic acid derivatives, which is a class of pyrethroids
insecticides.[23] Cyclobutylboronate 5b was converted to pri-
Silica-TRIP
100
113[c,e] (98)
7[f]
8[f]
Silica-SMAP
Silica-TRIP
80
80
77 (75)
0
[a] Conditions: 1 (0.4 mmol), 2 (0.2 mmol), [Ir(cod)(OMe)]2 (0.004 mmol Ir),
ligand (0.004 mmol P), THF (1 mL), 24 h. [b] Yields based on 2 were deter-
mined by 1H NMR spectroscopy. Isolated yield is in parentheses. Yields in
excess of 100% indicate that HBpin also worked as a borylating reagent
(theoretical maximum yield is 200%). [c] The Z isomers of substrates re-
mained intact in the crude mixture. [d] In THF (2 mL), for 15 h. [e] The C=
N reduction product of 3 was observed in the crude mixture (entry 5,
9%; entry 6, 4%). [f] In hexane (1 mL).
ceptional cis selectivity to afford cyclopropylboronate 3n (en-
tries 7 and 8). Coordination of the carbonyl oxygen atom to
the Ir atom is thought to be responsible for the regio- and ste-
reoselectivities.
Next, the Silica-SMAP–Ir system was applied to the CÀH bor-
ylation of cyclobutanes, which had not been reported previ-
ously. Results are summarized in Table 3. Reaction of 2-cyclobu-
tylpyridine (4a) occurred at 258C to give cyclobutylboronate
5a as the sole product (Table 3, entry 1). The borylation
showed exceptional cis selectivity, and no ring opening was
detected. N-Methylbenzoimidazole and benzooxazole were
also suitable directing groups (entries 2–4).[18] Gram-scale bory-
lation of 4b with a reduced catalyst loading (0.1 mol% Ir, at
808C) proceeded efficiently to give 5b in 94% isolated yield
(entry 3).
Scheme 3. Transformations of borylation products.
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mary alcohol 9 through the one-carbon-homologation/oxida-
tion sequence. These transformations occurred with retention
of configuration to give the corresponding 1,2-cis-disubstituted
small-ring compounds.[18]
[3] Metal-catalyzed CÀH functionalizations of cyclopropanes: a) A. Kubota,
M. S. Sanford, Synthesis 2011, 2579; b) M. Wasa, K. M. Engle, D. W. Lin,
E. J. Yoo, J.-Q. Yu, J. Am. Chem. Soc. 2011, 133, 19598; c) S. Rousseaux, B.
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2013, 15, 3238; i) D. S. Roman, A. B. Charette, Org. Lett. 2013, 15, 4394;
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Babu, J. Org. Chem. 2013, 78, 11911. See also refs [3c,d].
In summary, silica-supported monophosphane–Ir catalyst
systems enabled N- or O-atom-directed CÀH borylation of cy-
clopropanes and cyclobutanes. Borylation occurred with excep-
tional regio- and stereoselectivities with the assistance of vari-
ous directing groups, including N-heteroarenes, an oxime,
imine, and amide, resulting in formation of cis-substituted cy-
clopropyl- and cyclobutylboronates. The successful borylation
of sterically congested CÀH bonds of substituted cyclopro-
panes, including a tertiary CÀH bond, demonstrates the poten-
tial of this heterogeneous borylation strategy toward function-
alization of small-ring systems.
Experimental Section
[6] Stoichiometric CÀH funtionalizations of cyclopropanes and cyclobu-
tanes with organolithium or organomagnesium reagents: a) P. E. Eaton,
C.-H. Lee, Y. Xiong, J. Am. Chem. Soc. 1989, 111, 8016; b) M.-X. Zhang,
P. E. Eaton, Angew. Chem. 2002, 114, 2273; Angew. Chem. Int. Ed. 2002,
41, 2169; c) P. E. Eaton, M.-X. Zhang, N. Komiya, C.-G. Yang, I. Steele, R.
Gilardi, Synlett 2003, 1275.
Procedure for the borylation of 2-cyclopropylpyridine (1a)
with Silica-SMAP–Ir catalyst (Scheme 1)
In a nitrogen-filled glove box, Silica-SMAP (0.07 mmolgÀ1, 57.1 mg,
0.004 mmol, 2 mol%), bis(pinacolato)diboron (2) (50.8 mg,
0.2 mmol), and anhydrous, degassed THF (0.3 mL) were placed in
a 10 mL glass tube containing a magnetic stirring bar. A solution
of [Ir(cod)(OMe)]2 (1.3 mg, 0.002 mmol, 1 mol%) in THF (0.7 mL)
and 2-cyclopropylpyridine (1a) (47.7 mg, 0.4 mmol) were added
successively. The tube was sealed with a screw cap and removed
from the glove box. The reaction mixture was stirred at 258C for
15 h, and filtered through a glass pipette equipped with a cotton
filter. The solvent was removed under reduced pressure. An inter-
nal standard (1,1,2,2-tetrachloroethane) was added to the residue.
[7] Recent reviews on transition-metal-catalyzed CÀH borylation: a) I. A.
Mkhalid, J. H. Barnard, T. B. Marder, J. M. Murphy, J. F. Hartwig, Chem.
Rev. 2010, 110, 890; b) J. F. Hartwig, Chem. Soc. Rev. 2011, 40, 1992; c) A.
Ros, R. Fernꢂndez, J. M. Lassaletta, Chem. Soc. Rev. 2014, 43, 3229.
[8] Organoboron compounds as biologically active molecules: R. Smoum,
A. Rubinstein, V. M. Dembitsky, M. Srebnik, Chem. Rev. 2012, 112, 4156.
[9] Metal-catalyzed primary C(sp3)ÀH borylations: a) H. Chen, S. Schlecht,
T. C. Semple, J. F. Hartwig, Science 2000, 287, 1995; b) Y. Kondo, D.
Garcꢃa-Cuadrado, J. F. Hartwig, N. K. Boaen, N. L. Wagner, M. A. Hillmyer,
J. Am. Chem. Soc. 2002, 124, 1164; c) J. D. Lawrence, M. Takahashi, C.
Bae, J. F. Hartwig, J. Am. Chem. Soc. 2004, 126, 15334; d) J. M. Murphy,
J. D. Lawrence, K. Kawamura, C. Incarvito, J. F. Hartwig, J. Am. Chem.
Soc. 2006, 128, 13684; e) T. Ohmura, T. Torigoe, M. Suginome, J. Am.
Chem. Soc. 2012, 134, 17416; f) T. Ohmura, T. Torigoe, M. Suginome, Or-
ganometallics 2013, 32, 6170. Benzylic C(sp3)-H borylations; g) S. Shima-
da, A. S. Batsanov, J. A. K. Howard, T. B. Marder, Angew. Chem. 2001, 113,
2226; Angew. Chem. Int. Ed. 2001, 40, 2168; h) T. Ishiyama, K. Ishida, J.
Takagi, N. Miyaura, Chem. Lett. 2001, 30, 1082; i) T. A. Boebel, J. F. Hart-
wig, Organometallics 2008, 27, 6013.
1
The yields of the products 3a and 3a’ were determined by H NMR
spectroscopy (150 and 6% based on 2, respectively). The crude
material was then purified by Kugelrohr distillation (1 mmHg,
758C), to give the corresponding product 3a (65.4 mg, 0.27 mmol,
133% yield). Yields in excess of 100% indicate that HBpin formed
during catalytic turnover also worked as a borylating reagent (the-
oretical maximum yield is 200%).
[10] Metal-catalyzed secondary C(sp3)ÀH borylations: a) C. W. Liskey, J. F.
Hartwig, J. Am. Chem. Soc. 2012, 134, 12422; b) S. Kawamorita, T. Miya-
zaki, T. Iwai, H. Ohmiya, M. Sawamura, J. Am. Chem. Soc. 2012, 134,
12924; c) S. Kawamorita, R. Murakami, T. Iwai, M. Sawamura, J. Am.
Chem. Soc. 2013, 135, 2947; d) T. Mita, Y. Ikeda, K. Michigami, Y. Sato,
Chem. Commun. 2013, 49, 5601; e) S. H. Cho, J. F. Hartwig, J. Am. Chem.
Soc. 2013, 135, 8157; f) S. H. Cho, J. F. Hartwig, Chem. Sci. 2014, 5, 694.
See also ref. [4].
[11] For CÀC bond-forming transformations of cyclopropyl- and cyclobutyl-
trifluoroborates, see: a) G. A. Molander, P. E. Gormisky, J. Org. Chem.
2008, 73, 7481; b) G. A. Molander, V. Colombei, V. A. Braz, Org. Lett.
2011, 13, 1852.
Acknowledgements
This work was supported by a Grants-in-Aid for Scientific Re-
search on Innovative Areas “Organic Synthesis Based on Reac-
tion Integration” from MEXT, and by CREST and ACT-C from
JST.
Keywords: borylation
·
CÀH activation
· cyclobutanes ·
cyclopropanes · iridium catalysts
[12] Silica-SMAP and Silica-TRIP can be purchased from Wako Pure Chemical
Industries. For their applications, see refs. [10b,c].
[13] For the stereoselective synthesis of cyclopropyl- and cyclobutylboro-
nates through copper-catalyzed reactions of allyl and homoallyl alcohol
derivatives with 2, see: a) H. Ito, Y. Kosaka, K. Nonoyama, Y. Sasaki, M.
Sawamura, Angew. Chem. 2008, 120, 7534; Angew. Chem. Int. Ed. 2008,
47, 7424; b) C. Zhong, S. Kunii, Y. Kosaka, M. Sawamura, H. Ito, J. Am.
Chem. Soc. 2010, 132, 11440; c) H. Ito, T. Toyoda, M. Sawamura, J. Am.
Chem. Soc. 2010, 132, 5990.
[1] For cyclopropanes, see: a) The Chemistry of the Cyclopropyl Group (Eds.:
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4631.
[14] See the Supporting Information for ligand effects.
[15] The reaction using HBpin instead of 2 under otherwise identical reac-
tion conditions gave 3a in 77% yield.
[2] For cyclobutanes, see: a) The Chemistry of Cyclobutanes (Eds.: Z. Rappo-
port, J. F. Liebman), Wiley, Chichester, 2005; b) E. Lee-Ruff, G. Mladeno-
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[16] The presence or absence of an N–B interaction of the borylation prod-
ucts in solution was determined by 11B NMR spectroscopic analysis (see
the Supporting Information). See also: a) A. Ros, B. Estepa, R. Lꢄpez-Ro-
drꢃguez, E. ꢅlvarez, R. Fernꢂndez, J. M. Lassaletta, Angew. Chem. 2011,
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[20] The crude reaction mixture contained a significant amount of a byprod-
uct (2-cyclopropyl-1-methyl-2,3-dihydro-1H-benzoimidazole, 39%) re-
sulting from C=N reduction of the starting material (1e); however, the
borylation product 3e did not undergo C=N reduction. Therefore, 3e
could be isolated easily by bulb-to-bulb distillation.
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[18] CCDC-1005180 (3a’), CCDC-1005181 (3j), CCDC-1005182 (5b), and
CCDC-1005183 (8a) contain the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif. See the Supporting Information for details.
Received: July 11, 2014
Published online on && &&, 0000
Chem. Eur. J. 2014, 20, 1 – 6
www.chemeurj.org
5
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Communication
COMMUNICATION
Heteroatom-directed CÀH borylations
of small-ring carbocycles, such as cyclo-
propanes and cyclobutanes, were ach-
ieved with silica-supported monophos-
phane–Ir catalysts (see scheme). Boryla-
tion occurred at the CÀH bonds located
g to the directing N or O atoms with ex-
ceptional cis stereoselectivity relative to
the directing groups.
&
Organic Synthesis
R. Murakami, K. Tsunoda, T. Iwai,
M. Sawamura*
&& – &&
Stereoselective CÀH Borylations of
Cyclopropanes and Cyclobutanes with
Silica-Supported Monophosphane–Ir
Catalysts
&
&
Chem. Eur. J. 2014, 20, 1 – 6
www.chemeurj.org
6
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!