C-H Activation Induced by Oxidative Addition of N-O Bonds in Oxime Esters: Formation of Rhodacycles and Cycloaddition with Alkynes

Article abstract of DOI:10.1021/acs.organomet.6b00311

The reaction of oxime esters with a rhodium(I) precursor to form five-membered rhodacycles via N-O bond cleavage followed by C-H bond activation has been investigated by isolating these complexes. Kinetic studies on the formation of rhodacycles show that the reversible oxidative addition of the N-O bond in the oxime ester to RhCl(PPh₃)₃ occurs at room temperature. The E-isomer of the oxime ester was found to undergo rhodacycle formation faster than the Z-isomer, which suggests that the geometry of the oxime esters reflects the geometry of intermediates during C-H activation. The rhodacycle reacted with an alkyne to construct an isoquinoline ring in both stoichiometric and catalytic conditions, despite its basic stability in air, in moisture, and even during heating, which demonstrates the potential of the rhodacycle as an intermediate for further catalytic transformation of oxime esters.

Full text of DOI:10.1021/acs.organomet.6b00311

Article
pubs.acs.org/Organometallics
C−H Activation Induced by Oxidative Addition of N−O Bonds in
Oxime Esters: Formation of Rhodacycles and Cycloaddition with
Alkynes
Takuya Shimbayashi, Kazuhiro Okamoto,* and Kouichi Ohe*
Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto
615-8510, Japan
S
* Supporting Information
ABSTRACT: The reaction of oxime esters with a rhodium(I) precursor
to form five-membered rhodacycles via N−O bond cleavage followed by
C−H bond activation has been investigated by isolating these complexes.
Kinetic studies on the formation of rhodacycles show that the reversible
oxidative addition of the N−O bond in the oxime ester to RhCl(PPh3)3
occurs at room temperature. The E-isomer of the oxime ester was found
to undergo rhodacycle formation faster than the Z-isomer, which
suggests that the geometry of the oxime esters reflects the geometry of
intermediates during C−H activation. The rhodacycle reacted with an
alkyne to construct an isoquinoline ring in both stoichiometric and
catalytic conditions, despite its basic stability in air, in moisture, and even
during heating, which demonstrates the potential of the rhodacycle as an
intermediate for further catalytic transformation of oxime esters.
have been no reports on the isolation of the intermediate
complexes of these transition metals.
INTRODUCTION
■
Recent progress in transition-metal-catalyzed transformation
reactions of oximes and their derivatives has extended their
synthetic utility in various nitrogen-containing organic
compounds.1 The key step for these reactions is the oxidative
addition of their N−O bonds to low-valent metal species
(Scheme 1). The stoichiometric oxidative addition of simple
We investigated the rhodium-mediated reaction of oxime
esters, which involves the oxidative addition of oxime esters to
rhodium(I), and found that the rhodacycle complexes were
formed by the oxidative addition of oxime esters to rhodium(I)
followed by C−H activation (Scheme 2).
Scheme 2. Rhodium-Mediated Oxidative Cleavage of Oxime
Esters to Form Rhodacycles
Scheme 1. Oxidative Addition of N−O Bonds of Oxime
Derivatives to Low-Valent Metal Species
oximes to rhenium, osmium, and titanium was reported
previously.2 In 1999, Narasaka et al.3 reported a palladium-
catalyzed intramolecular amino-Heck reaction involving
oxidative addition of oxime esters to palladium(0) species as
a landmark study. Many transformation reactions using this
concept have since been reported.4,5 Recently, a few
distinguished mechanistic studies have reported that the
involvement of the oxidative addition of oxime esters to
palladium(0) was confirmed by the isolation of oxidative
adducts.4b,g Although other transition metals such as rhodium,
copper, nickel, ruthenium, and iridium have also been studied
in terms of their use as a catalyst in similar reactions,6−8 there
RESULTS AND DISCUSSION
■
As an initial attempt, a stoichiometric reaction of O-pivaloyl
oxime ester (E)-1 and RhCl(PPh3)3 in C6D6 at room
temperature was traced with 1H NMR (Figure 1). Immediately
after mixing, a new doublet peak corresponding to the methyl
protons of the isopropyl group was observed in the high-field
Received: April 18, 2016
© XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.6b00311
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Figure 1. 1H NMR spectra of time dependence of the reaction of (E)-1 (0.02 mmol) with RhCl(PPh3)3 (0.02 mmol) in C6D6 at room temperature.
region, which was assigned to rhodacycle 2. As the reaction
proceeded, another doublet peak assigned to rhodacycle 3 was
also observed in the high-field region. The yellow crystals of
rhodacycle 3 precipitated after 24 h.9 Complex 2, bearing a
pivalate ligand, was not isolated from this reaction mixture, but
was successfully prepared in high yield from the isolated
complex 3 by the treatment of silver pivalate (eq 1). In
Figure 2. ORTEP illustrations of complex 2. Left: Hydrogen atoms are
omitted for clarity. Right: Phenyl groups on phosphorus atoms are
omitted for clarity.
addition, isolated complex 2 was also converted back to
complex 3 by the treatment of RhCl(PPh3)3, which indicates
that interconversion between two rhodacycles occurred in the
reaction as shown in Figure 1. Finally, rhodacycle 3 was
obtained almost quantitatively by adding Me3SiCl as a chloride
source after the completion of the reaction of oxime ester 1 and
RhCl(PPh3)3 (eq 2).
Rhodacycles 2 and 3 were characterized by X-ray crystallo-
Figure 3. ORTEP illustration of complex 3. Hydrogen atoms and
graphic analysis (Figures 2 and 3). Two PPh3 ligands of both
solvent molecules are omitted for clarity.
rhodacycle complexes 2 and 3 were located at the axial
positions to a rhodacycle plane, and two chloride ligands were
located on the rhodacycle plane. It is worth noting that the η1-
pivalate ligand of rhodacycle 2 is located at the cis position to an
imine nitrogen whose proton forms the obvious hydrogen bond
with the pivalate oxygen (the length of O···N = 2.82 Å).
The difference in reactivity between two stereoisomers of
oxime ester 1 was examined with a reaction in diluted
conditions where RhCl(PPh3)3 was dissolved sufficiently (eq
3). Oxime ester (E)- or (Z)-1 was consumed within 2 h upon
mixing to afford the same rhodacycles 2 and 3 in each case. The
reaction of (E)-1 showed an obviously faster reaction rate than
that of (Z)-1 (Figure 4). The reaction rates of both isomers of
oxime ester 1 (kobs) were calculated using the inverse plot of a
concentration of oxime ester 1 against time, which showed a
linear relationship in the condition of an identical initial
concentration of oxime ester 1 and RhCl(PPh3)3 (Figures S4
and S9, see Supporting Information). These results show the
B
DOI: 10.1021/acs.organomet.6b00311
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
in which one of the two reactive hydrogens is deuterated,
reacted with RhCl(PPh3)3 to give a mixture of 3-d1 and 3
totally in 50% yield with a 72:28 ratio (eq 4; KIE value = 2.57).
In contrast to the intramolecular control experiment, an
intermolecular competitive experiment using (E)-1 and (E)-1-
d5 resulted in a less significant KIE value (eq 5; KIE value =
1.44).
A proposed mechanism for the formation of rhodacycle
complexes is shown in Scheme 3. The oxidative addition of the
Scheme 3. Proposed Mechanism for Generation of
Rhodacycles from Oxime Ester 1
Figure 4. Time dependence of percentage amounts of each species in
the reaction of (E)-1 (a) or (Z)-1 (b) (8.1 μmol) with RhCl(PPh3)3
(8.1 μmol) in C6D6 (0.8 mL) at room temperature. The percentage
1
amounts were determined by H NMR using hexamethylbenzene as
an internal standard.
first-order dependence of these reactions on both 1 and
RhCl(PPh3)3. Moreover, the activation parameters were
calculated from Arrhenius and Eyring plots with the traces of
the reactions at various temperatures (range 10−55 °C)
(Figures S12 and S13, see Supporting Information). The
calculated values of activation energies were 19.9 kcal/mol for
(E)-1 and 22.8 kcal/mol for (Z)-1, which are consistent with
the result that the reactions proceeded smoothly at room
temperature. The calculated values for activation enthalpy were
19.3 kcal/mol for (E)-1 and 22.2 kcal/mol for (Z)-1, and those
for activation entropy were −4.48 × 10−3 kcal/mol·K for (E)-1
and 2.64 × 10−3 kcal/mol·K for (Z)-1. The activation entropies
in the rhodacycle formation did not affect the total energy
difference significantly.
N−O bond of oxime ester (E)- or (Z)-1 is likely to be initiated
by the dissociation of one PPh3 and the following η1-
coordination of the oxime nitrogen atom to rhodium(I) species
(coordination of the carbonyl oxygen may also participate in
this step)10 and then forms intermediate A or A′, depending on
the geometry of the starting oxime esters.11 Considering the
distance between the rhodium center and the C−H bond at the
Competitive experiments using oxime esters labeled with
deuterium have been performed to observe kinetic isotope
effects (KIEs) in the rhodacycle formation. Substrate (E)-1-d,
C
DOI: 10.1021/acs.organomet.6b00311
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
ortho position of the phenyl group, C−H activation in complex
A is much preferred than in complex A′. Complex A′ needs to
isomerize into complex A prior to C−H activation, which may
become a major factor for decreasing the reaction rate from
oxime ester (Z)-1. This explanation agrees with the apparent
difference in activation parameters between both stereoisomers
of oxime ester 1. After the oxidative addition step, activation of
ortho C−H bonds is considered to proceed in a concerted
metalation−deprotonation mechanism12 induced by the η1-
pivalate ligand to afford five-membered rhodacycle B. Rhoda-
cycle B is readily protonated at the iminide nitrogen by the
pivalic acid to give pivalate-coordinated complex 2. The ligand
exchange between chloride and pivalate on complex 2 affords
dichloride complex 3, as described previously. The large KIE
value observed in the intramolecular comparison using (E)-1-d
indicates that the N−O bond cleavage would be a rate-
determining step because it occurs before the C−H activation
step.13,14 The small KIE value observed in the intermolecular
comparison may indicate the reversibility of N−O bond
cleavage that occurs before the C−H activation.15
Scheme 4. Formation of Chloro-Bridged Dimer 5 in the
Presence of Diphenylacetylene
The reactivity of rhodacycle complex 3 with an excess
amount of 4-octyne was examined. Isoquinoline 4 as a
cycloaddition product was obtained in 50% yield by the
reaction of complex 3 with 20 equiv of 4-octyne in xylene at
150 °C (eq 6). Moreover, a rhodium-catalyzed reaction of
Figure 5. ORTEP illustration of rhodacycle dimer 5. Hydrogen atoms
are omitted for clarity.
Scheme 5. Proposed Mechanism for Alkyne Insertion Giving
Isoquinoline 4
oxime ester (E)-1 with 4-octyne also proceeded to afford
isoquinoline 4 in 31% yield (eq 7).16 As a remarkable result, the
reaction of complex 3 with diphenylacetylene formed no
insertion products, but formed chloro-bridged dimer complex 5
in high yield (Scheme 4). The ORTEP drawing of 5 is shown in
Figure 5. The simple heating of complex 3 in the absence of
diphenylacetylene also gave only the dimer complex 5 in 29%
yield, which indicates that the alkyne promotes the dissociation
of PPh3, leading to the formation of dimer complex 5.
On the basis of the observation of the stoichiometric and
catalytic reactions with alkynes involving rhodacycles, we
propose a reaction mechanism for the formation of isoquinoline
4 (Scheme 5). Considering the formation of dimer complex 5,
the reaction with 4-octyne would be initiated by the ligand
exchange between PPh3 and 4-octyne. When the alkyne
dissociates from the resulting intermediate C, a thermally
more stable chloro-bridged dimer 5 is formed. When
intermediate C undergoes alkyne insertion into a carbon−
rhodium σ-bond, a seven-membered rhodacycle D is formed.
Under high-temperature conditions, intermediate D is consid-
ered to be in an equilibrium with dehydrochlorinated
rhodacycle E, which undergoes reductive elimination to give
isoquinoline 4 as a product as well as the regeneration of
rhodium(I) catalyst.17,18 This stoichiometric reaction of
complex 3 strongly supports the intermediacy of a five-
membered rhodacycle.
D
DOI: 10.1021/acs.organomet.6b00311
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Chem. Soc. 2013, 135, 13664−13667. (h) Zhu, J.-L.; Wu, S.-T.; Shie, J.-
Y. J. Org. Chem. 2014, 79, 3623−3633. (i) Zhang, Z.-W.; Lin, A.; Yang,
J. J. Org. Chem. 2014, 79, 7041−7050. (j) Faulkner, A.; Scott, J. S.;
Bower, J. F. J. Am. Chem. Soc. 2015, 137, 7224−7230. (k) Chen, C.;
Hou, L.; Cheng, M.; Su, J.; Tong, X. Angew. Chem., Int. Ed. 2015, 54,
3092−3096. (l) Race, N. J.; Faulkner, A.; Shaw, M. H.; Bower, J. F.
Chem. Sci. 2016, 7, 1508−1513.
(5) In our previous work, transition-metal-catalyzed transformation
of isoxazol-5(4H)-ones (cyclic oxime esters) was investigated in which
oxidative addition and decarboxylative formation of nitrene complexes
are proposed as key steps. See: (a) Okamoto, K.; Oda, T.; Kohigashi,
S.; Ohe, K. Angew. Chem., Int. Ed. 2011, 50, 11470−11473.
(b) Okamoto, K.; Shimbayashi, T.; Tamura, E.; Ohe, K. Chem. -
Eur. J. 2014, 20, 1490−1494. (c) Shimbayashi, T.; Okamoto, K.; Ohe,
K. Synlett 2014, 25, 1916−1920. (d) Okamoto, K.; Shimbayashi, T.;
Yoshida, M.; Nanya, A.; Ohe, K. Angew. Chem., Int. Ed., in press, doi:
10.1002/anie.201602241.
CONCLUSION
■
In summary, we have achieved isolation and identification of
the rhodacycle complexes by the reaction of a rhodium
precursor and aromatic oxime esters. The oxidative addition of
the N−O bonds in the oxime esters plays two characteristic
roles in the rhodacycle formation: (1) the rhodium center is
strongly attached to the nitrogen atom with the covalent bond;
therefore, it is close to the aromatic C−H bond; (2) the valency
of the rhodium center was changed into the higher oxidation
state; therefore, it reduces the barrier to C−H activation.
Moreover, the potential of the rhodacycles as an intermediate
for the cycloaddition of alkynes with oxime esters has also been
demonstrated. Further investigations for the effective catalytic
transformation of oxime esters are currently under way in our
laboratory.
(6) For recent reports on rhodium-catalyzed transformation reactions
of oxime derivatives involving N−O bond cleavage, see ref 10b and:
(a) Parthasarathy, K.; Cheng, C.-H. J. Org. Chem. 2009, 74, 9359−
9364. (b) Too, P. C.; Wang, Y.-F.; Chiba, S. Org. Lett. 2010, 12, 5688−
5691. (c) Zhang, X.; Chen, D.; Zhao, M.; Zhao, J.; Jia, A.; Li, X. Adv.
Synth. Catal. 2011, 353, 719−723. (d) Zhao, P.; Wang, F.; Han, K.; Li,
X. Org. Lett. 2012, 14, 3400−3403. (e) Hou, W.; Zhou, B.; Yang, Y.;
Feng, H.; Li, Y. Org. Lett. 2013, 15, 1814−1817. (f) Neely, J. M.;
Rovis, T. J. Am. Chem. Soc. 2014, 136, 2735−2738. (g) Zhao, D.; Lied,
F.; Glorius, F. Chem. Sci. 2014, 5, 2869−2873. (h) Nakamura, I.; Sato,
Y.; Takeda, K.; Terada, M. Chem. - Eur. J. 2014, 20, 10214−10219.
(7) For recent reports on copper-catalyzed transformation reactions
of oxime derivatives involving N−O bond cleavage, see: (a) Liu, S.;
Yu, Y.; Liebeskind, L. S. Org. Lett. 2007, 9, 1947−1950. (b) Too, P. C.;
Chua, S. H.; Wong, S. H.; Chiba, S. J. Org. Chem. 2011, 76, 6159−
6168. (c) Ren, Z.-H.; Zhang, Z.-Y.; Yang, B.-Q.; Wang, Y.-Y.; Guan, Z.-
H. Org. Lett. 2011, 13, 5394−5397. (d) Zhao, M.-N.; Liang, H.; Ren,
Z.-H.; Guan, Z.-H. Synthesis 2012, 44, 1501−1506. (e) Nakamura, I.;
Kudo, Y.; Araki, T.; Zhang, D.; Kwon, E.; Terada, M. Synthesis 2012,
44, 1542−1550. (f) Wei, Y.; Yoshikai, N. J. Am. Chem. Soc. 2013, 135,
3756−3759. (g) Nakamura, I.; Kudo, Y.; Terada, M. Angew. Chem., Int.
Ed. 2013, 52, 7536−7539. (h) Tang, X.; Huang, L.; Qi, C.; Wu, W.;
Jiang, H. Chem. Commun. 2013, 49, 9597−9599. (i) Faulkner, A.;
Race, N. J.; Scott, J. S.; Bower, J. F. Chem. Sci. 2014, 5, 2416−2421.
(j) Tang, X.; Huang, L.; Yang, J.; Xu, Y.; Wu, W.; Jiang, H. Chem.
Commun. 2014, 50, 14793−14796. (k) Su, H.; Li, W.; Xuan, Z.; Yu, W.
Adv. Synth. Catal. 2015, 357, 64−70.
(8) For other transition-metal-catalyzed transformation of oxime
derivatives involving N−O bond cleavage, see: Ni: (a) Yoshida, Y.;
Kurahashi, T.; Matsubara, S. Chem. Lett. 2011, 40, 1140−1142.
(b) Yoshida, Y.; Kurahashi, T.; Matsubara, S. Chem. Lett. 2012, 41,
1498−1499. Fe: (c) Deb, I.; Yoshikai, N. Org. Lett. 2013, 15, 4254−
4257. Ru: (d) Kornhaaß, C.; Li, J.; Ackermann, L. J. Org. Chem. 2012,
77, 9190−9198. (e) Zhao, M.-N.; Hui, R.-R.; Ren, Z.-H.; Wang, Y.-Y.;
Guan, Z.-H. Org. Lett. 2014, 16, 3082−3085. Ir: (f) Nishimura, T.;
Yoshinaka, T.; Nishiguchi, Y.; Maeda, Y.; Uemura, S. Org. Lett. 2005,
7, 2425−2427.
(9) Similar imine-containing five-membered rhodacycles bearing two
phosphine ligands at axial positions were reported. See: (a) Huang, L.-
Y.; Aulwurm, U. R.; Heinemann, F. W.; Knoch, F.; Kisch, H. Chem. -
Eur. J. 1998, 4, 1641−1646. (b) Marcazzan, P.; Patrick, B. O.; James,
B. R. Organometallics 2005, 24, 1445−1451. (c) Ezhova, M. B.; Patrick,
B. O.; James, B. R. Organometallics 2005, 24, 3753−3757.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.6b00311.
■
S
Experimental procedures for preparation of oxime esters
and rhodacycle complexes; procedures for stoichiometric
and catalytic reactions; and NMR spectroscopic data
(PDF)
X-ray crystallographic data for the oxime and rhodium
complexes 2, 3, and 5 (CIF)
AUTHOR INFORMATION
Corresponding Authors
*E-mail: kokamoto@scl.kyoto-u.ac.jp.
*E-mail: ohe@scl.kyoto-u.ac.jp.
Notes
■
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This study has been financially supported by JSPS KAKENHI
(Grant-in-Aid for Young Scientists (B); Grant No. 24750085).
The authors thank Prof. Tetsuaki Fujihara (Kyoto University)
for his support with NMR measurements and X-ray crystallo-
graphic analyses. Helpful and suggestive comments from the
reviewers are gratefully appreciated.
REFERENCES
■
(1) For reviews, see: (a) Kitamura, M.; Narasaka, K. Chem. Rec. 2002,
2, 268−277. (b) Narasaka, K.; Kitamura, M. Eur. J. Org. Chem. 2005,
2005, 4505−4519. (c) Huang, H.; Ji, X.; Wu, W.; Jiang, H. Chem. Soc.
Rev. 2015, 44, 1155−1171. (d) Huang, H.; Cai, J.; Deng, G.-J. Org.
Biomol. Chem. 2016, 14, 1519−1530.
(2) (a) Tillack, A.; Arndt, P.; Spannenberg, A.; Kempe, R.; Rosenthal,
U. Z. Anorg. Allg. Chem. 1998, 624, 737−740. (b) Ferreira, C. M. P.;
Guedes da Silva, M. F. C.; Kukushkin, V. Y.; Frausto, J. J. R.;
́
Pombeiro, A. J. L. J. Chem. Soc., Dalton Trans. 1998, 325−326.
(3) Tsutsui, H.; Narasaka, K. Chem. Lett. 1999, 28, 45−46.
(10) One might think about the possibility of another mechanism in
which the C−H activation occurs first and then the oxidative addition
of N−O bonds follows (see also ref 6b). However, in the case of
rhodium(I) complexes, such a mechanism can be excluded by the
result that other oxime derivatives such as oxime ethers (no N−O
bond cleavage occurs) did not give any C−H activation products
under similar conditions.
(4) For recent studies on palladium-catalyzed transformation
reactions of oxime derivatives involving N−O bond cleavage, see:
(a) Gerfaud, T.; Neuville, L.; Zhu, J. Angew. Chem., Int. Ed. 2009, 48,
572−577. (b) Tan, Y.; Hartwig, J. F. J. Am. Chem. Soc. 2010, 132,
3676−3677. (c) Kitamura, M.; Moriyasu, Y.; Okauchi, T. Synlett 2011,
22, 643−646. (d) Faulkner, A.; Bower, J. F. Angew. Chem., Int. Ed.
2012, 51, 1675−1679. (e) Faulkner, A.; Scott, J. S.; Bower, J. F. Chem.
Commun. 2013, 49, 1521−1523. (f) Race, N. J.; Bower, J. F. Org. Lett.
2013, 15, 4616−4619. (g) Hong, W. P.; Iosub, A. V.; Stahl, S. S. J. Am.
(11) Selected examples of ortho C−H activation by rhodiium(III)
directed by an N-oxyimino or imino group. See: (a) Fukutani, T.;
E
DOI: 10.1021/acs.organomet.6b00311
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Umeda, N.; Hirano, K.; Satoh, T.; Miura, M. Chem. Commun. 2009,
5141−5143. (b) Sun, Z.-M.; Chen, S.-P.; Zhao, P. Chem. - Eur. J. 2010,
16, 2619−2627. (c) Tsai, A. S.; Brasse, M.; Bergman, R. G.; Ellman, J.
A. Org. Lett. 2010, 13, 540−542. (d) Qin, D.; Wang, J.; Qin, X.; Wang,
C.; Gao, G.; You, J. Chem. Commun. 2015, 51, 6190−6193 See also ref
6.
(12) For reviews, see: (a) Lapointe, D.; Fagnou, K. Chem. Lett. 2010,
39, 1118−1126. (b) Bouffard, J.; Itami, K. Top. Curr. Chem. 2009, 292,
231−280. (c) Ackermann, L. Chem. Rev. 2011, 111, 1315−1345.
(d) Sperger, T.; Sanhueza, I. A.; Kalvet, I.; Schoenebeck, F. Chem. Rev.
2015, 115, 9532−9586.
(13) Simmons, E. M.; Hartwig, J. F. Angew. Chem., Int. Ed. 2012, 51,
3066−3072.
(14) The possibility that the coordination of rhodium to oxime esters
is rate-determining cannot be excluded with the present results.
(15) The E/Z isomerization of oxime esters was also observed in the
reaction of (E)-1-d5 with RhCl(PPh3)3 (Figure S14 in the Supporting
Information) despite no thermal isomerization of these oxime esters
under the reaction conditions. This result is also consistent with the
reversibility of N−O bond cleavage.
(16) For eqs 6 and 7, see the screening of the reaction conditions in
the Supporting Information.
(17) Isoquinoline synthesis by the stoichiometric alkyne insertion to
a five-membered rhodacycle intermediate with a Cp* ligand has been
reported by Jones et al. See: Li, L.; Brennessel, W. W.; Jones, W. D. J.
Am. Chem. Soc. 2008, 130, 12414−12419.
(18) For reviews on rhodium(III)-catalyzed formation of isoquino-
lines via a five-membered rhodacycle intermediate, see: (a) He, R.;
Huang, Z.-T.; Zheng, Q.-Y.; Wang, C. Tetrahedron Lett. 2014, 55,
5705−5713. (b) Mo, J.; Wang, L.; Liu, Y.; Cui, X. Synthesis 2015, 47,
439−459 See also ref 6.
F
DOI: 10.1021/acs.organomet.6b00311
Organometallics XXXX, XXX, XXX−XXX