The oxidative annulation of tertiary benzyl alcohols with internal alkynes using an (electron-deficient η5-cyclopenta-dienyl)rhodium(III) catalyst under ambient conditions

Article abstract of DOI:10.1002/adsc.201400084

It has been established that a dinuclear (electron-deficient η⁵-cyclopentadienyl)rhodium(III) complex catalyzes the oxidative annulation of tertiary benzyl alcohols with internal alkynes via sp² C-H/O-H functionalization under ambient conditions (at room temperature under air) to give substituted isochromenes in good yields. The preference for annulation across electron-rich substrates over electron-deficient substrates was observed using this electron-deficient rhodium(III) complex.

Full text of DOI:10.1002/adsc.201400084

UPDATES
DOI: 10.1002/adsc.201400084
The Oxidative Annulation of Tertiary Benzyl Alcohols with
Internal Alkynes using an (Electron-Deficient h5-Cyclopenta-
dienyl)Rhodium(III) Catalyst under Ambient Conditions
G
Miho Fukui,a Yuki Hoshino,a Tetsuya Satoh,b,c Masahiro Miura,b
and Ken Tanakaa,c,*
a
Department of Applied Chemistry, Graduate School of Engineering, Tokyo University of Agriculture and Technology,
Koganei, Tokyo 184-8588, Japan
E-mail: tanaka-k@cc.tust.ac.jp
Department of Applied Chemistry, Faculty of Engineering, Osaka University, Suita, Osaka 565-0871, Japan
b
c
Japan Science and Technology Agency (JST), ACT-C, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan
Received: January 23, 2014; Published online: May 7, 2014
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201400084.
Abstract: It has been established that a dinuclear
(electron-deficient
h5-cyclopentadienyl)rhodium-
(III) complex catalyzes the oxidative annulation of
tertiary benzyl alcohols with internal alkynes via sp2
C H/O H functionalization under ambient condi-
tions (at room temperature under air) to give sub-
stituted isochromenes in good yields. The prefer-
ence for annulation across electron-rich substrates
over electron-deficient substrates was observed
lysts.[3,4] In their initial communication, the reactions
of acetanilides with internal alkynes were conducted
at high temperature (1208C) using an in situ generat-
ACHTUNGTRENNUNG
ed dicationic rhodium
from [Cp*RhCl2]2, as a catalyst and a stoichiometric
amount of Cu(OAc)2 as an oxidant to give the corre-
ACHTUNGTNER(NUNG III)/Cp* complex, derived
À
À
AHCTUNGTRENNUNG
sponding indoles in good yields (conditions A,
Scheme 1).[3a] In their subsequent article, the same re-
actions proceeded at lower temperature (608C) in
higher yields by using an isolated dicationic rhodium-
using this electron-deficient rhodiumACTHUNRTGNEUNG(III) complex.
AHCTNURTGEG(NUNN III)/Cp* complex, [Cp*RhAHCTNURTGEG(NNUN MeCN)3]ACHTNUGTREN[UNGN SbF6]2, as a cata-
lyst, with O2 and a catalytic amount of Cu
ACHTUNGRTEN(NUNG OAc)2 as
À
Keywords: alkynes; annulation; benzyl alcohols; C
H bond functionalization; rhodium
oxidants (conditions B, Scheme 1).[3b]
On the other hand, our research group recently re-
ported the synthesis of an (ethoxycarbonyl-substituted
cyclopentadienyl)rhodiumACHTNUGRTNEUNG
(III) complex [CpERhX2
(1), Scheme 2] via the rhodium(I)-catalyzed cross-
[2+2+1]cyclotrimerization of silylacetylenes and two
alkynyl esters, leading to substituted silylfulvenes, fol-
Introduction
Dicationic rhodiumACTHNUTRGNEUNG
(III)/Cp* complexes,[1] derived lowed by reductive complexation with RhCl3 in etha-
from [Cp*RhCl2]2, are highly active catalysts for num- nol.[5] It was anticipated that an in situ generated elec-
[2]
À
bers of C H bond functionalization reactions. For tron-deficient dicationic rhodium
N
example, Fagnou and co-workers reported the oxida- derived from 1, would show higher catalytic activity
tive annulation of acetanilides with internal alkynes than the dicationic rhodium
N
À
using dicationic rhodium
N
Scheme 1. Fagnouꢀs oxidative annulation of acetanilides with internal alkynes using dicationic rhodiumACTHNUTRGNEUNG
(III)/Cp* catalysts.[3]
1638
ꢁ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2014, 356, 1638 – 1644

UPDATES
The Oxidative Annulation of Tertiary Benzyl Alcohols with Internal Alkynes
Scheme 2. Our research groupꢀs oxidative annulation of acetanilides with internal alkynes using a dicationic rhodiumACHTUNGTRENNUNG(III)/
CpE catalyst.[7]
Results and Discussion
We first examined the reaction of 2-phenyl-2-propa-
nol (2a) with diphenylacetylene (3a) using an in situ
generated electron-deficient dicationic rhodium
CpE complex, derived from 1 (2.5 mol%), as a catalyst,
with air and a catalytic amount of Cu(OAc)2 as oxi-
ACHTUNGTRENNUNG(III)/
AHCTUNGTRENNUNG
dants at room temperature for 24 h. Pleasingly, the
desired oxidative annulation reaction proceeded to
give the corresponding isochromene in moderate
yield (4aa, Scheme 4). Prolonged reaction time (72 h)
increased the yield of 4aa (Scheme 4). The catalytic
Scheme 3. Oxidative annulation of tertiary benzyl alcohols
with internal alkynes using the dicationic rhodium
ACHTUNGTRENN(UNG III)/Cp*
catalyst.[9]
activities of the rhodium
strates. Indeed, this new electron-deficient rhodium- were compared under the same reaction conditions.
(III) complex catalyzed the oxidative annulation of As shown in Scheme 4, the activity of the rhodium-
acetanilides with internal alkynes at room tempera-
(III)/CpE complex was significantly higher than that
ture under air (Scheme 2).[7,8] On the contrary, the of the rhodium
(III)/Cp* complex.
electron-deficient rhodium(III) complex 1 was not As shown in Scheme 5, this rhodium-catalyzed oxi-
(III)/CpE and Cp* complexes
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
À
a suitable precatalyst for the C H bond functionaliza- dative annulation under the above mild reaction con-
tion of electron-deficient substrates, such as benz- ditions showed a wide scope with respect to both ter-
A
tiary benzyl alcohols 2 and internal alkynes 3, al-
The above successful application of the electron-de- though higher catalyst loadings (5 mol% of 1) were
À
ficient rhodium
tionalization prompted our investigation into the C
G
À
H bond functionalization of another electron-rich variety of diarylacetylenes 3a–3f reacted with 2a to
substrate. Satoh and Miura recently reported the oxi- give the corresponding isochromenes 4aa–4af in good
dative annulation of tertiary benzyl alcohols 2 with in- to high yields. In terms of regioselectivity, the use of
ternal alkynes 3, leading to isochromenes 4, via sp2 arylacetylene 3e possessing sterically different aryl
C H/O H functionalization by using the isolated di- groups showed good regioselectivity and the sterically
cationic rhodium(III)/Cp* complex, [Cp*Rh(MeCN)3] demanding naphthyl group is mainly located in the 4-
[SbF6]2, as a catalyst and an excess amount of
Cu(OAc)2 as an oxidant at high temperature
(Scheme 3).[9–11] We anticipated that the electron-defi-
cient rhodium(III) complex 1 would be a highly
À
À
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
active precatalyst for this oxidative annulation reac-
tion and promote this reaction under ambient condi-
tions (at room temperature under air).
In this paper, we wish to present the oxidative an-
nulation of tertiary benzyl alcohols with internal al-
2
À
À
kynes via sp C H/O H functionalization by using
the (electron-deficient h5-cyclopentadienyl)rhodi-
Scheme 4. Oxidative annulation of 2a with 3a using 1 vs.
[Cp*RhCl2]2.
um
(III) catalyst under ambient conditions.[12]
Adv. Synth. Catal. 2014, 356, 1638 – 1644
ꢁ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
1639

UPDATES
Miho Fukui et al.
Scheme 5. Oxidative annulation of tertiary benzyl alcohols 2a–2h with internal alkynes 3a–3n using rhodium
1 under ambient conditions.
ACHTUNGTREN(NUNG III) complex
position of the product isochromene 4ae. Unfortu- symmetrical diarylacetylene 3f, possessing electroni-
nately, poor regioselectivity was observed using un- cally different aryl groups. Not only diaryl- but also
1640
asc.wiley-vch.de
ꢁ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2014, 356, 1638 – 1644

UPDATES
The Oxidative Annulation of Tertiary Benzyl Alcohols with Internal Alkynes
Scheme 6. Oxidative annulation of secondary benzyl alcohol 2i with 3a.
aryl-alkylacetylenes 3g–3l reacted with 2a to give the
corresponding isochromenes 4ag–4al in high yields
with moderate to high regioselectivities. In the reac-
tions of aryl-alkylacetylenes 3g–3k, the aryl groups
are mainly located in the 3-position of the product
isochromenes 4ag–4ak. On the contrary, in the reac-
tion of the highly sterically demanding tert-butyl-sub-
stituted internal alkyne 3l, the aryl group is located in
the 4 position of the product isochromene 4al. It is
worthy of note that unstable cyclopropyl-substituted
alkyne 3j could be employed for this reaction. Impor-
tantly, dialkylacetylene 3m showed very low reactivity
Scheme 7. Oxidative annulation of tertiary allyl alcohol 6
with 3a.
in the Cp*Rh
synthesis,[13] on the contrary, dialkylacetylenes 3m and lyst in refluxing dioxane to give the corresponding
3n reacted with 2a in the presence of the CpERh(III) 2H-pyran 7 in moderate yield.[9] Unfortunately, the
catalyst to give the corresponding isochromenes 4am present ambient reaction conditions using 1 as the
and 4an, respectively, in high yields. precatalyst were not effective for the above transfor-
The scope of tertiary benzyl alcohols was next ex- mation (Scheme 7).
amined. The 2-, 3-, and 4-methyl-substituted benzyl A plausible mechanism for the rhodium
alcohols 2b–2d reacted with 3a to give the corre- lyzed isochromene synthesis is shown in Scheme 8.[9]
sponding isochromenes 4ba–4da in high yields. It is Rhodium(III) complex A reacts with tertiary benzyl
ACHTUNGTRENNUNG(III) complex-catalyzed isochromene tion with 3a using the [Cp*RhACHTUNRTGENG(NUN MeCN)3]ACHTNUGTERN[NUGN SbF6]2 cata-
AHCTUNGTRENNUNG
AHCTUNGTRENNG(UN III)-cata-
AHCTUNGTRENNUNG
worthy of note that the reaction of 3-methyl-substitut- alcohol 2 to generate rhodium
(III) alkoxide B. Intra-
À
ed benzyl alcohol 2c proceeded with perfect regiose- molecular C H bond cleavage proceeds to produce
lectivity and that of sterically demanding 3-methyl- the five-membered oxarhodacycle C. Coordination
substituted benzyl alcohol 2c proceeded in high yield. followed by migratory insertion of internal alkyne 3
Not only electron-rich methyl-substituted benzyl alco- occurs to afford the seven-membered oxarhodacycle
À
hols but also electron-deficient 4-chloro-substituted D. Then, C O bond reductive elimination affords the
benzyl alcohol 2e reacted with 3a to give the corre- desired isochromene 4 along with rhodium(I) complex
sponding isochromene 4ea in good yield. Not only E. This rhodium(I) complex E is then oxidized back
benzene derivatives but also 2-(2-naphthyl)-2-propa- to the active rhodium
nol (2f), which showed poor reactivity towards 3a in acetate and the resulting copper(I) acetate is then re-
the Cp*Rh(III) complex-catalyzed isochromene syn- oxidized by molecular oxygen.
thesis,[14] reacted with 3a to give the corresponding
ACHTUNGTNER(NUNG III) complex A with copper(II)
ACHTUNGTRENNUNG
It was expected that electron-deficient rhodium
(III)
À
isochromene 4fa in high yield, although 4fa was ob- complex A would facilitate the C H bond cleavage of
tained as a mixture of regioisomers. Finally, the reac- electron-rich substrates over electron-deficient sub-
tions of 1,1-diphenylethanol (2g) and triphenylmetha- strates. Indeed, in the previous report, we have dem-
nol (2h) with 3a were examined. Although these reac- onstrated that the intermolecular competition experi-
tions were sluggish, the desired isochromenes 4ga and ment between electron-deficient and electron-rich
4ha were obtained in moderate yields.
anilides with diphenylacetylene using 1 as a precatalyst
The reaction of secondary benzyl alcohol 2i with 3a reveals the preference for annulation across the elec-
was also examined. Unfortunately, dehydrogenation, tron-rich anilide over the electron-deficient anilide.[7]
rather than the oxidative annulation, of 2i proceeded Additionally, we have demonstrated that the intermo-
predominantly to give acetophenone (5) as a major lecular competition experiment between electron-de-
product and isochromene 4ia as a minor product ficient diarylacetylene and electron-rich dialkylacety-
(Scheme 6).
lene with anilide using 1 as a precatalyst reveals the
In the previous report by Satoh and Miura, tertiary preference for migratory insertion across dialkylacety-
allyl alcohol 6 also underwent the oxidative annula- lene over diarylacetylene.[7]
Adv. Synth. Catal. 2014, 356, 1638 – 1644
ꢁ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
1641

UPDATES
Miho Fukui et al.
Scheme 8. Plausible mechanism for the formation of isochromene 4.
Scheme 9. Competition experiments between electron-deficient and electron-rich benzyl alcohols 2b and 2e using 1 vs.
[Cp*RhCl2]2.
Thus, similar intermolecular competition experi- deficient diarylacetylene 3a and electron-rich dialkyl-
ments were conducted between electron-deficient and
ACHTUNGTRENUNaNG cetylene 3n as shown in Scheme 9 and Scheme 10.
electron-rich benzyl alcohols 2b and 2e, and electron- The use of electron-deficient complex 1 revealed the
Scheme 10. Competition experiments between diaryl- and dialkylacetylenes 3a and 3n using 1 vs. [Cp*RhCl2]2.
1642
asc.wiley-vch.de
ꢁ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2014, 356, 1638 – 1644

UPDATES
The Oxidative Annulation of Tertiary Benzyl Alcohols with Internal Alkynes
1,1-Dimethyl-3,4-diphenyl-1H-isochromene (4aa):[9]:Color-
less solid. 1H NMR (CDCl3, 500 MHz): d=7.41–7.11 (m,
13H), 6.96–6.90 (m, 1H), 1.84 (s, 6H); 13C NMR (CDCl3,
125 MHz): d=148.2, 137.2, 136.4, 136.2, 132.1, 131.8, 128.9,
128.7, 127.9, 127.6, 127.4, 127.1, 127.0, 123.7, 122.3, 115.8,
77.8, 27.2; HR-MS (APCI): m/z=313.1597, calcd. for
C23H21O [M+H]+: 313.1587.
preference for the annulation across electron-rich
benzyl alcohol 2b over electron-deficient benzyl alco-
hol 2e and the same preference was also revealed in
the case of using electron-rich [Cp*RhCl2]2
(Scheme 9). The use of 1 revealed the slight prefer-
ence for the migratory insertion across dialkylacety-
lene 3n over diarylacetylene 3a (Scheme 10); on the
contrary, the use of [Cp*RhCl2]2 revealed the slight
preference for the migratory insertion across 3a over
3n (Scheme 10).
Acknowledgements
This work was supported partly by Grants-in-Aid for Scien-
tific Research from the Ministry of Education, Culture,
Sports, Science and Technology (MEXT, Japan) (Nos.
23105512, 25105714, and 251057733) and ACT-C from Japan
Science and Technology Agency (JST, Japan). We thank
Umicore for generous support in supplying the rhodium com-
plex.
Conclusions
In conclusion, it has been established that a dinuclear
(electron-deficient h5-cyclopentadienyl)rhodium
ACTHNUTRGNE(NUG III)
complex is a highly active precatalyst for the oxida-
tive annulation of tertiary benzyl alcohols with inter-
nal alkynes, leading to isochromenes, under ambient
conditions (at room temperature under air). The pres-
ent catalysis could be conducted using air and a cata-
References
lytic amount of CuACHTUNTRGNEUNG(OAc)2 as oxidants in acetone at
room temperature, therefore, this new protocol is op-
erationally more convenient than the previously re-
[1] For reviews of (h5-cyclopentadienyl)rhodium
ACTHUNTGRENNG(U III) com-
plexes, see: a) E. Peris, P. Lahuerta, in: Comprehensive
Organometallic Chemistry III, Vol. 7, (Eds.: H. C.
Robert, D. M. P. Mingos), Elsevier, Oxford, 2007,
p 139; b) P. M. Maitlis, J. Organomet. Chem. 1995, 500,
239.
ported protocol [employing excess CuACTHNURGTNEUNG(OAc)2 as an
oxidant in refluxing dioxane]. This study revealed
that our new CpERhX2 precatalyst (1) is more active
À
À
[2] For reviews of the rhodium-catalyzed C H bond func-
for the directed C H bond functionalization of elec-
tron-rich arenes, including not only anilides[7] but also
benzyl alcohols, than the conventional Cp*RhX2 pre-
catalyst. The preference for annulation across elec-
tron-rich substrates over electron-deficient substrates,
which is similar to the previously studied indole syn-
thesis,[7] was observed in the electron-deficient dicat-
tionalization, see: a) G. Song, F. Wang, X. Li, Chem.
Soc. Rev. 2012, 41, 3651; b) F. W. Patureau, J. Wencel-
Delord, F. Glorius, Aldrichimica Acta 2012, 45, 31;
c) D. A. Colby, A. S. Tsai, R. G. Bergman, J. A. Ellman,
Acc. Chem. Res. 2012, 45, 814; d) T. Satoh, M. Miura,
Chem. Eur. J. 2010, 16, 11212; e) J. C. Lewis, R. G.
Bergman, J. A. Ellman, Acc. Chem. Res. 2008, 41, 1013.
[3] a) D. R. Stuart, M. Bertrand-Laperle, K. M. N. Burgess,
K. Fagnou, J. Am. Chem. Soc. 2008, 130, 16474;
b) D. R. Stuart, P. Alsabeh, M. Kuhn, K. Fagnou, J.
Am. Chem. Soc. 2010, 132, 18326.
ionic rhodium
mene synthesis.
ACHTUNGTRENNUNG
(III)/CpE complex-catalyzed isochro-
À
[4] For examples of the transition metal-catalyzed C H
bond functionalization of anilides, see: a) J. Wencel-
Delord, C. Nimphius, H. Wang, F. Glorius, Angew.
Chem. 2012, 124, 13175; Angew. Chem. Int. Ed. 2012,
51, 13001; b) H. Wang, C. Grohmann, C. Nimphius, F.
Glorius, J. Am. Chem. Soc. 2012, 134, 19592; c) T.-S.
Jiang, G.-W. Wang, J. Org. Chem. 2012, 77, 9504; d) B.
Schmidt, N. Elizarov, Chem. Commun. 2012, 48, 4352;
e) B. Xiao, Y.-M. Li, Z.-J. Liu, H.-Y. Yang, Y. Fu,
Chem. Commun. 2012, 48, 4854; f) F. Zhou, X. Han, X.
Lu, Tetrahedron Lett. 2011, 52, 4681; g) M. P. Huestis,
L. Chan, D. R. Stuart, K. Fagnou, Angew. Chem. 2011,
123, 1374; Angew. Chem. Int. Ed. 2011, 50, 1338; h) Y.
Su, M. Zhao, G. Song, X. Li, Org. Lett. 2010, 12, 5462;
i) T. W. Lyons, M. S. Sanford, Chem. Rev. 2010, 110,
1147; j) R. J. Phipps, M. J. Gaunt, Science 2009, 323,
1593; k) Z. Shi, B. Li, X. Wan, J. Cheng, Z. Fang, B.
Cao, C. Qin, Y. Wang, Angew. Chem. 2007, 119, 5650;
Angew. Chem. Int. Ed. 2007, 46, 5554; l) S. Yang, B. Li,
X. Wan, Z. Shi, J. Am. Chem. Soc. 2007, 129, 6066;
m) X. Wan, Z. Ma, B. Li, K. Zhang, S. Cao, S. Zhang,
Experimental Section
Typical Procedure for RhodiumACTHNUTRGNEUNG(III)-Catalyzed
Oxidative Annulation of Tertiary Benzyl Alcohols
with Internal Alkynes under Ambient Conditions
(4aa, Scheme 4 and Scheme 5)
To a 13.5-mL screw-cap vial bottle was added AgSbF6
(6.9 mg,
0.020 mmol),
1
(4.3 mg,
0.0050 mmol),
Cu(OAc)2·H2O (8.0 mg, 0.040 mmol), 2-phenylpropan-2-ol
ACHTUNGTRENNUNG
(2a, 81.7 mg, 0.600 mmol), diphenylacetylene (3a, 35.6 mg,
0.200 mmol), and acetone (1.0 mL) under air in this order.
The vessel was sealed and the mixture stirred at room tem-
perature under air for 72 h. The resulting mixture was dilut-
ed with ether, filtered through a silica gel pad, and washed
with EtOAc. The solvent was concentrated under reduced
pressure and the residue was purified by a preparative TLC
(hexane/EtOAc/toluene/CH2Cl2 =40:1:5:5) to give 4aa;
yield: 57.8 mg (0.185 mmol, 93%).
Adv. Synth. Catal. 2014, 356, 1638 – 1644
ꢁ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
1643

UPDATES
Miho Fukui et al.
Z. Shi, J. Am. Chem. Soc. 2006, 128, 7416; n) V. G.
Zaitsev, O. Daugulis, J. Am. Chem. Soc. 2005, 127,
4156.
[9] K. Morimoto, K. Hirano, T. Satoh, M. Miura, J. Org.
Chem. 2011, 76, 9548.
[10] For another example of the oxidative annulation of
a benzyl alcohol with alkynes, see: a) T. Uto, M. Shimi-
zu, K. Ueura, H. Tsurugi, T. Satoh, M. Miura, J. Org.
Chem. 2008, 73, 298. For the oxidative annulation of 1-
naphthols or 1-hydroxyisoquinoline with alkynes, see:
b) S. Mochida, M. Shimizu, K. Hirano, T. Satoh, M.
Miura, Chem. Asian J. 2010, 5, 847; c) G. Song, D.
Chen, C.-L. Pan, R. H. Crabtree, X. Li, J. Org. Chem.
2010, 75, 7487.
[5] a) Y. Shibata, K. Tanaka, Angew. Chem. 2011, 123,
11109; Angew. Chem. Int. Ed. 2011, 50, 10917. As a re-
lated cyclotrimerization reaction, our research group
reported the synthesis of substituted dihydropentalenes
by the rhodium-catalyzed cross-cyclotrimerization of
propargyl esters and two arylacetylenes. See: b) Y. Shi-
bata, K. Noguchi, K. Tanaka, Org. Lett. 2010, 12, 5596.
[6] Rovis and Hyster tested a trifluoromethyl-substituted
cyclopentadienyl rhodium
N
[11] The palladium-catalyzed arylation of a,a-disubstituted
À
À
the oxidative pyridine synthesis, while both the product
yield and regioselectivity were low. See: T. K. Hyster,
T. Rovis, Chem. Commun. 2011, 47, 11846.
arylmethanols via cleavage of a C C or a C H bond
has been reported, see: Y. Terao, H. Wakui, M.
Nomoto, T. Satoh, M. Miura, M. Nomura, J. Org.
Chem. 2003, 68, 5236.
[7] Y. Hoshino, Y. Shibata, K. Tanaka, Adv. Synth. Catal.
2014, 356, 1577–1585.
[8] For the use of air as a terminal oxidant in the rhodium-
À
[12] For a review of the metal-catalyzed C H bond activa-
tion under mild conditions, see: J. Wencel-Delord, T.
Drçge, F. Liu, F. Glorius, Chem. Soc. Rev. 2011, 40,
4740.
ACHTUNGTRENNUNG(III)-catalyzed olefination of acetanilides, see: a) F. W.
Patureau, F. Glorius, J. Am. Chem. Soc. 2010, 132,
9982; b) Y. Wang, C. Li, Y. Li, F. Yin, X.-S. Wang, Adv.
Synth. Catal. 2013, 355, 1724.
[13] In ref.[9] isochromene 4am was obtained in 36% yield.
[14] In ref.[9] isochromene 4fa was obtained in 43% yield.
1644
asc.wiley-vch.de
ꢁ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2014, 356, 1638 – 1644