Decarbonylation through Aldehydic C-H Bond Cleavage by a Cationic Iridium Catalyst

Article abstract of DOI:10.1055/s-0037-1611802

We report the decarbonylation of aldehydes through an aldehydic C-H bond cleavage catalyzed by a cationic iridium/bisphosphine catalyst. The reaction proceeds under relatively mild conditions to give the corresponding hydrocarbon products in moderate to high yields. In addition, this cationic iridium catalyst system can be applied to an asymmetric hydroacylation of ketones.

Full text of DOI:10.1055/s-0037-1611802

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©
Georg Thieme Verlag Stuttgart · New York
2019, 30, A–E
letter
A
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Synlett
T. Shirai et al.
Letter
Decarbonylation through Aldehydic C–H Bond Cleavage by a
Cationic Iridium Catalyst
Tomohiko Shirai*a
Kazuki Sugimotob
Masaya Iwasakib
Ryuki Sumidab
0
0
0
0-0
0
0
1-
7
6
6
9-0
2
8
8
R
H
+
cat. Ir(I) /xyl-BINAP
R
H
O
135 °C
– CO
15 examples
28–91% yield
R = aryl, alkyl
Harunori Fujitaa
Yasunori Yamamotoc
a
Department of Social Design Engineering, National Institute of Technology,
Kochi College, 200-1 Monobe, Nankoku, Kochi 783-8508, Japan
shirai@kochi-ct.ac.jp
Department of Materials Science and Engineering, National Institute of
Technology, Kochi College, 200-1 Monobe, Nankoku, Kochi 783-8508,
Japan
b
c
Division of Chemical Process Engineering and Frontier Chemistry Center
(
FCC), Faculty of Engineering, Hokkaido University, Kita 13 Nishi 8 Kitaku,
Sapporo, Hokkaido 060-8628, Japan
Received: 28.02.2019
Accepted after revision: 01.04.2019
Published online: 12.04.2019
of a neutral iridium catalyst to give the corresponding de-
10c
carbonylated products in good yields [Scheme 1(a)].
A
DOI: 10.1055/s-0037-1611802; Art ID: st-2019-k0121-l
wide range of functional groups are tolerated in this reac-
tion. Recently, a decarbonylation of aldehydes by using
earth-abundant nickel as a catalyst was also developed.
Abstract We report the decarbonylation of aldehydes through an al-
dehydic C–H bond cleavage catalyzed by a cationic iridium/bisphos-
phine catalyst. The reaction proceeds under relatively mild conditions to
give the corresponding hydrocarbon products in moderate to high
yields. In addition, this cationic iridium catalyst system can be applied
to an asymmetric hydroacylation of ketones.
11
More recently, a cobalt-mediated decarbonylation of alde-
12
hydes has been reported by Tonzetich and co-workers. Al-
though there are many active catalyst systems for this de-
carbonylation, a common feature of most of these reactions
is their use of neutral metal complexes. However, it is
known that cationic complexes can promote the decarbon-
ylation by decreasing -backdonation from the metal center
to an antibonding orbital of CO.7a
Key words decarbonylation, iridium catalysis, aldehydes, C–H bond
cleavage, asymmetric catalysis, hydroacylation
Transition-metal-catalyzed carbonylation with inex-
(
a) Report by Tsuji et al. (2008)
pensive carbon monoxide (CO) gas is one of the most com-
mon industrial processes for the synthesis of bulk and fine
[
Ir(cod)Cl]2
PPh3
Me
1
chemicals. Similarly, transition-metal-catalyzed decarbon-
1,4-dioxane, reflux
ylation of carbonyl compounds is a fundamental reaction in
synthetic chemistry, because it can be applied in beneficial
C–C bond-formation processes, such as cross-coupling reac-
O
9–96 h
P
P
Me
Me
2
2
R
R H
H
[Ir(cod)2](BArF4)
xyl-BINAP
2–4
tions. In addition, the decarbonylation reaction is also re-
garded as an efficient method for attractive C–C bond-
Me
THF, 135 °C
(R)-xyl-BINAP
24 h
5
cleavage reactions. Among these, the decarbonylation of
(b) This work
aldehydes is a basic decarbonylation reaction that has been
known for a long time. A stoichiometric rhodium-mediated
simple decarbonylation of aldehydes was first developed by
Scheme 1 Iridium-catalyzed decarbonylations of aldehydes
6
Tsuji and Ohno in 1965. Decarbonylation of aldehydes with
Here, we describe the development of a new cationic
iridium-catalyzed reaction for the decarbonylation of alde-
hydes that has a broad substituent compatibility [Scheme
1(b)].
various transition-metal catalysts has since become well
5a,6b,7–12
established.
In 2008, Tsuji and co-workers reported
that aromatic and aliphatic aldehydes react in the presence
©
Georg Thieme Verlag Stuttgart · New York — Synlett 2019, 30, A–E

B
Synlett
T. Shirai et al.
Letter
Table 1 Screening of Reaction Conditions for Catalytic Decarbonylation
(R)-Xyl-BINAP, led to further improvements in the reactivi-
ty, giving yields of 69 and 75%, respectively. However, dppf
was not a suitable ligand (entry 7). Furthermore, in contrast
OEt
O
OEt
Ir cat 5 mol%
ligand 5.5 mol%
H
H
to the result reported by Tsuji, the use of PPh , a monoden-
3
solvent, 135 °C, 24 h
tate phosphorus ligand, significantly lowered the decarbon-
ylation efficiency (entry 8). The solvent had some effect on
the reactivity, and the highest yield was obtained from the
reaction in THF (entry 9).
1a
2a
O
PPh2
PPh2
PPh2
PPh2
PAr2
PAr2
O
O
PPh2
PPh2
Fe
Table 2 Cationic Iridium-Catalyzed Decarbonylations of Aldehydesa
O
rac-BINAP (R)-Tol-BINAP (Ar = 4-Tol)
R)-Xyl-BINAP (Ar = 3,5-xylyl)
(R)-segphos
dppf
O
Ir(cod)2](BArF4) 5 mol%
[
(
H
xyl-BINAP 5.5 mol%
H
FG
FG
a
THF, 135 °C, 24 h
Entry
Catalyst
Ligand
Solvent
Yield (%)
1
FG = functional group
2
1
2
3
4
5
6
7
8
9
[Ir(cod)
[Ir(cod)
2
](BArF
](BF
4
)
rac-BINAP
rac-BINAP
rac-BINAP
(R)-Tol-BINAP
(R)-Xyl-BINAP
(R)-segphos
dppf
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
THF
68
32
18
69
75
61
7
b
Entry
1
Aldehyde
Product
Yield (%)
2
4
)
[IrCl(cod)]
2
OEt
O
O
O
OEt
](BArF
](BArF
](BArF
](BArF
](BArF
)
)
)
)
)
H
[Ir(cod)
[Ir(cod)
[Ir(cod)
[Ir(cod)
[Ir(cod)
2
2
2
2
2
4
4
4
4
4
78
H
1a
2a
2b
OBn
OAc
OBn
OAc
OH
c
H
H
H
35
2
3
H
H
1b
9c,d
6
PPh
3
4
[Ir(cod)
2
](BArF
4
)
(R)-Xyl-BINAP
(R)-Xyl-BINAP
(R)-Xyl-BINAP
78
64
10
[Ir(cod)
[Ir(cod)
2
](BArF
](BArF
4
4
)
)
DME
n.r.e
71
1c
2c
11
2
1,4-dioxane 77
a
Yield by GC with an internal standard (methyl 3-nitrobenzoate).
OH
NH2
O
O
4
H
2d
1
d
e
We initially chose 2-ethoxybenzaldehyde (1a) as a mod-
el substrate and we attempted its decarbonylation in the
presence of [Ir(cod) ](BAr ) (cod = cyclooctadienyl; Ar =
,5-bis(trifluoromethyl)phenyl) (5 mol%) and rac-BINAP
NH2
F
F
H
2
4
5
H
28
1
2e
2f
3
(
5.5 mol%) in toluene at 135 °C. (Note: we previously con-
MeO2C
AcHN
O
CO2Me
firmed that the chirality of ligand does not affected the re-
activity.) Under these conditions, the decarbonylation pro-
ceeded to give ethoxybenzene (2a) in 68% yield (Table 1, en-
try 1). The reaction with [Ir(cod) ](BF ) as a catalyst
precursor resulted in an obvious decrease in the yield (en-
try 2). Note also that the neutral iridium/rac-BINAP com-
plex performed poorly for decarbonylation under the opti-
mized conditions (entry 3). It is known that decarbonyla-
tion by the [Ir(coe) Cl] /rac-BINAP (coe = cyclooctene)
system requires a higher temperature (>160 °C) to give the
desired product because this transformation by a neutral
Ir/bisphosphine complex probably proceeds through partial
dissociation of the rac-BINAP ligand to generate a coordina-
tively unsaturated active species, as reported by the Mad-
H
37c
63c
6
H
1f
g
2
4
O
NHAc
H
7
H
2g
1
Me2NOC
Et2NOC
O
CONMe2
c
f
2
2
H
91
8
H
1
h
2h
49
O
CONEt2
H
32c
9
H
1i
2i
10f
10c
sen group. Furthermore, both the Tsuji group and the
10f
Ac
O
Ac
Madsen group showed that active species in neutral-Ir-
catalyzed decarbonylations contain fewer than two phos-
phines coordinated to iridium. A change from rac-BINAP to
its analogues (entries 4–6), in particular, (R)-Tol-BINAP and
H
65c
10
H
1j
2j
©
Georg Thieme Verlag Stuttgart · New York — Synlett 2019, 30, A–E

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Synlett
T. Shirai et al.
Letter
Table 2 (continued)
ing meta- or para-substituted benzaldehydes 1k–m, which
gave ethoxybenzene (2a) in moderate to good yields (en-
tries 11–13). Our method could also be applied to the de-
carbonylation of the sterically congested aldehyde 2n (en-
try 14). Aliphatic aldehydes 1o and 1p also underwent de-
carbonylation with this catalytic system to give 2o and 2p
in yields of 49 and 71%, respectively (entries 15 and 16).
The mechanism of the decarbonylation is already well
established, as shown in Scheme 2.
b
Entry
Aldehyde
Product
Yield (%)
O
O
EtO
H
H
2
a
EtO
1
1
2
H
H
59
72
1
k
2
a
1
1l
EtO
EtO
OEt
O
H
O
Ar
O
OEt
Ir
– CO
– Ir
Ar
Ar
Ir
Ar
H
H
C–H
migratory
extrusion
reductive
Ir
H
H
1m
2a
cleavage
elimination
13
83
49
H
Scheme 2 Proposed catalytic cycle for the decarbonylation of aldehydes
H
O
H
CH3
O
CH3
Lastly, we also briefly investigated the use of various re-
active species for decarbonylation, such as an acyliridium–
H
H
1n
2n
1
1
4
hydride intermediate generated in situ by aldehydic C–H
MeO
CH3
MeO
CH3
bond cleavage.7
f,10f
Because asymmetric hydroacylation of
CH3
CH3
ketones catalyzed by rhodium1
3a–d
or cobalt
13e
complexes
CH3
CH3
had been previously reported, we presumed that the asym-
metric hydroacylation occurs via an acyliridium–hydride
complex. In fact, the cationic iridium-catalyzed atom-eco-
nomical asymmetric hydroacylation of 2-acetylbenzalde-
hyde (1j) proceeded to give the corresponding chiral phtha-
lide 3 in 57% conversion and with good enantioselectivity
H
5
2o
49
71
Ph
1o
Ph
O
H3C
H
H3C
CH3
2p
1p
16
7
7
O
a
Reaction conditions: aldehyde 1 (0.25 mmol), Ir cat (5 mol%), (R)-Xyl-
(70% ee) (Scheme 3). The cationic property of the iridium
BINAP (1.1 equiv on Ir) THF, 24 h, 135 °C, stirring, sealed tube.
b
GC yield.
complex was beneficial for its use in an asymmetric hy-
droacylation, whereas the neutral complex did not catalyze
the reaction. To our knowledge, this reaction represents the
first example of an iridium-catalyzed asymmetric hydroac-
c
Isolated yield.
d
4
8 h.
e
f
n.r. = no reaction.
3
A [IrCl(cod)] /PPh system was used for comparison purposes.
2
14
ylation of a ketone through aldehydic C–H bond cleavage.
With an optimized catalytic system in hand, we next ex-
plored its versatility by employing a variety of aldehydes 1
Table 2). Note that in all cases of low to moderate yields,
O
O
Ir precursor 5 mol%
H
(R)-xyl-BINAP 5.5 mol%
(
H
O
O
∗
O
the unreacted starting materials were recovered and no by-
products, including the Tishchenko reaction product,11
were obtained. 2-Alkoxybenzaldehydes (1a and 1b) were
tolerated, and the corresponding hydrocarbons (2a and 2b)
were obtained in moderate to good yield (entries 1 and 2).
Unexpectedly, the acetoxy-substituted substrate 1c showed
no reaction, and the starting material was recovered quan-
titatively. The decarbonylation products 2d and 2e were ob-
tained in moderate to good yields despite the presence of
unprotected hydroxy and amino groups, respectively. (en-
tries 4 and 5) Moreover, moderate to high yields were ob-
tained from the reactions of benzaldehydes 1f–j possessing
ester, amide, or ketone substituents (entries 6–10). In par-
ticular, the use of cationic iridium system was beneficial for
the decarbonylation of 1h, which has a coordinating amide
substituent, compared with corresponding reaction in the
presence of the neutral iridium system ([IrCl(cod)] /PPh ).
THF, 90 °C, 48 h
H
1j
3
H3C
2j
CH3
CH3
trace
n.d.
[Ir(cod) ](BArF )
2
4
:
:
57%, 70% ee
n.d.
[Ir(cod)Cl]2
Scheme 3 Asymmetric hydroacylation of a ketone
In summary, we have reported a new efficient system
for the decarbonylation through aldehydic C–H bond cleav-
age by using a cationic iridium/bidentate phosphine cata-
lyst.15 The cationic iridium catalyst system is synthetically
useful, as demonstrated by the asymmetric hydroacylation
of a ketone to give a chiral five-membered lactones. We
are currently working to develop new cationic iridium-cat-
alyzed synthetic methods involving C–H bond cleavage.
16
2
3
Subsequent screening experiments were performed by us-
©
Georg Thieme Verlag Stuttgart · New York — Synlett 2019, 30, A–E

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Synlett
T. Shirai et al.
Letter
Funding Information
(6) (a) Tsuji, J.; Ohno, K. Tetrahedron Lett. 1965, 6, 3969. (b) Ohno,
K.; Tsuji, J. J. Am. Chem. Soc. 1968, 90, 99.
Support has been provided in part by the TAKE SYSTEMS CO., LTD.
T
A
K
E
S
Y
S
T
E
M
S
C
O
.
,
L
T
D
.
()
(
7) For Rh catalysis, see: (a) Doughty, D. H.; Pignolet, L. H. J. Am.
Chem. Soc. 1978, 100, 7083. (b) Abu-Hasanayn, F.; Goldman, M.
E.; Goldman, A. S. J. Am. Chem. Soc. 1992, 114, 2520. (c) Beck, C.
M.; Rathmill, S. E.; Park, Y. J.; Chen, J.; Crabtree, R. H.; Liable-
Sands, L. M.; Rheingold, A. L. Organometallics 1999, 18, 5311.
Supporting Information
Supporting information for this article is available online at
https://doi.org/10.1055/s-0037-1611802.
(d) Kreis, M.; Palmelund, A.; Bunch, L.; Madsen, R. Adv. Synth.
S
u
p
p
orit
n
g Inform ati
o
n
S
u
p
p
orti
n
g Inform ati
o
n
Catal. 2006, 348, 2148. (e) Fessard, T. C.; Andrews, S. P.;
Motoyoshi, H.; Carreira, E. M. Angew. Chem. Int. Ed. 2007, 46,
9
331. (f) Fristrup, P.; Kreis, M.; Palmelund, A.; Norrby, P.-O.;
References and Notes
Madsen, R. J. Am. Chem. Soc. 2008, 130, 5206. (g) Taaring, E.;
Madsen, R. Chem. Eur. J. 2008, 14, 5638.
(1) For carbonylation and decarbonylation reactions, see:
(
8) For Pd catalysis, see: (a) Hawthorne, J. O.; Wilt, M. H. J. Org.
Chem. 1960, 25, 2215. (b) Wilt, J. W.; Pawlikowski, W. W. Jr.
J. Org. Chem. 1975, 40, 3641. (c) Matsubara, S.; Yokota, Y.;
Oshima, K. Org. Lett. 2004, 6, 2071. (d) Ferri, D.; Mondelli, C.;
Krumeich, F.; Baiker, A. J. Phys. Chem. B 2006, 110, 22982.
Fukuyama, T.; Maetani, S.; Ryu, I. In Comprehensive Organic Syn-
thesis II Vol. 3, Chap. 3.22; Knochel, P.; Molander, G. A., Ed.; Else-
vier: Amsterdam, 2014, 1073.
(
2) For metal-catalyzed decarbonylative C–C bond-formation reac-
tions of aldehydes, see: (a) Varela, J. A.; González-Rodríguez, C.;
Rubin, S. G.; Castedo, L.; Saá, C. J. Am. Chem. Soc. 2006, 128,
(e) Chatterjee, M.; Ishizaka, T.; Kawanami, H. Green Chem. 2018,
20, 2345.
9
1
576. (b) Guo, X.; Wang, J.; Li, C.-J. J. Am. Chem. Soc. 2009, 131,
5092. (c) Guo, X.; Wang, J.; Li, C.-J. Org. Lett. 2010, 12, 3176.
(
9) For Ru catalysis, see: (a) Domazetis, G.; Tarpey, B.; Dorphin, D.;
James, B. R. J. Chem. Soc., Chem. Commun. 1980, 939. (b) Park, K.
H.; Son, S. U.; Chung, Y. K. Chem. Commun. 2003, 1898.
(d) Shuai, Q.; Yang, L.; Guo, X.; Baslé, O.; Li, C.-J. J. Am. Chem. Soc.
2010, 132, 12212. (e) Yang, L.; Correia, C. A.; Guo, X.; Li, C.-J. Tet-
(c) Mazziotta, A.; Madsen, R. Eur. J. Org. Chem. 2017, 5417.
rahedron Lett. 2010, 51, 5486. (f) Yang, L.; Zeng, T.; Shuai, Q.;
Guo, X.; Li, C.-J. Chem. Commun. 2011, 47, 2161. (g) Kang, L.;
Zhang, F.; Ding, L.-T.; Yang, L. RSC Adv. 2015, 5, 100452.
(
10) For Ir catalysis, see: (a) Shibata, T.; Toshida, N.; Yamasaki, M.;
Maekawa, S.; Takagi, K. Tetrahedron 2005, 61, 9974. (b) Kwong,
F. Y.; Lee, H. W.; Lam, W. H.; Qiu, L.; Chan, A. S. C. Tetrahedron:
Asymmetry 2006, 17, 1238. (c) Iwai, T.; Fujihara, T.; Tsuji, Y.
Chem. Commun. 2008, 6215. (d) Geilen, F. M. A.; vom Stein, T.;
Engendahl, B.; Winterle, S.; Liauw, M. A.; Klankermayer, J.;
Leitner, W. Angew. Chem. Int. Ed. 2011, 50, 6831. (e) Adams, J. J.;
Arulsamy, N.; Roddick, D. M. Organometallics 2012, 31, 1439.
(h) Tomberg, A.; Kundu, S.; Zhou, F.; Li, C.-J.; Moitessier, N. ACS
Omega 2018, 3, 3218.
(
3) For recent examples of decarbonylative radical C–C bond-for-
mation reactions of aldehydes, see: (a) Paul, S.; Guin, J. Chem.
Eur. J. 2015, 21, 17618. (b) Tang, R. J.; He, Q.; Yang, L. Chem.
Commun. 2015, 51, 5925. (c) Tang, R.-J.; Kang, L.; Yang, L. Adv.
Synth. Catal. 2015, 357, 2055. (d) Zong, Z.; Wang, W.; Bai, X.; Xi,
H.; Li, Z. Asian J. Org. Chem. 2015, 4, 622. (e) Yang, L.; Lu, W.;
Zhou, W.; Zhang, F. Green Chem. 2016, 18, 2941. (f) Ouyang, X.-
H.; Song, R.-J.; Liu, B.; Li, J.-H. Adv. Synth. Catal. 2016, 358, 1903.
(f) Olsen, E. P. K.; Singh, T.; Harris, P.; Andersson, P. G.; Madsen,
R. J. Am. Chem. Soc. 2015, 137, 834.
(
(
(
11) For Ni catalysis, see: Ding, K.; Xu, S.; Alotaibi, R.; Paudel, K.;
Reinheimer, E. W.; Weatherly, J. J. Org. Chem. 2017, 82, 4924.
12) Co-mediated decarbonylation: Alawisi, H.; Al-Afyouni, K. F.;
Arman, H. D.; Tonzetich, Z. J. Organometallics 2018, 37, 4128.
13) For atom-economical asymmetric hydroacylations of ketones,
see: (a) Shen, Z.; Khan, H. A.; Dong, V. M. J. Am. Chem. Soc. 2008,
(
(
g) Lv, L.; Bai, X.; Yan, X.; Li, Z. Org. Chem. Front. 2016, 3, 1509.
h) Biswas, P.; Paul, S.; Guin, J. Angew. Chem. Int. Ed. 2016, 55,
7756. (i) Pan, C.; Chen, Y.; Song, S.; Li, L.; Yu, J.-T. J. Org. Chem.
2016, 81, 12065. (j) Pan, C.; Chen, C.; Yu, J.-T. Org. Biomol. Chem.
2017, 15, 1096. (k) Li, Y.-X.; Wang, Q.-Q.; Yang, L. Org. Biomol.
130, 2916. (b) Phan, D. H. T.; Kim, B.; Dong, V. M. J. Am. Chem.
Soc. 2009, 131, 15608. (c) Shen, Z.; Dornan, P. K.; Khan, H. A.;
Woo, T. K. Dong V. M. J. Am. Chem. Soc. 2009, 131, 1077.
Chem. 2017, 15, 1338. (l) Li, W.-Y.; Wang, Q.-Q.; Yang, L. Org.
Biomol. Chem. 2017, 15, 9987. (m) Liu, X.; Qian, P.; Wang, Y.;
Pan, Y. Org. Chem. Front. 2017, 4, 2370. (n) Li, Y.-X.; Li, W.-Y.;
Jiang, Y.-Y.; Yang, L. Tetrahedron Lett. 2018, 59, 2934. (o) Biswas,
P.; Guin, J. J. Org. Chem. 2018, 83, 5629. (p) Li, Y.; Li, J.-H. Org.
Lett. 2018, 20, 5323. (q) Zou, H.-X.; Li, Y.; Yang, X.-H.; Xiang, J.;
Li, J.-H. J. Org. Chem. 2018, 83, 8581. (r) Luo, Z.; Han, X.; Fang, Y.;
Liu, P.; Feng, C.; Li, Z.; Xu, X. Org. Chem. Front. 2018, 5, 3299.
(d) Khan, H. A.; Kou, K. G. M.; Dong, V. M. Chem. Sci. 2011, 2,
407. (e) Yang, J.; Yoshikai, N. J. Am. Chem. Soc. 2014, 136, 16748.
(
14) For recent examples of enantioselective insertions of ketone
C=O groups into Ir–H bonds, see: (a) Yoshida, K.; Kamimura, T.;
Kuwabara, H.; Yanagisawa, A. Chem. Commun. 2015, 51, 15442.
(b) Ak, B.; Aydemir, M.; Durap, F.; Meriç, N.; Elma, D.; Baysal, A.
Tetrahedron: Asymmetry 2015, 26, 1307. (c) Verkade, J. M. M.;
Quaedflieg, P. J. L. M.; Verzijl, G. K. M.; Lefort, L.; vanDelft, F. L.;
de Vries, J. G.; Rutjes, F. P. J. T. Chem. Commun. 2015, 51, 14462.
(s) Tang, S.; Liu, Y.; Gao, X.; Wang, P.; Huang, P.; Lei, A. J. Am.
Chem. Soc. 2018, 140, 6006. (t) Wu, C.-S.; Li, R.; Wang, Q.-Q.;
Yang, L. Green Chem. 2019, 21, 269.
(d) Liu, W.-P.; Yuan, M.-L.; Yang, X.-H.; Li, K.; Xie, J.-H.; Zhou, Q.-
(
4) For selected reviews of decarbonylative transformation of other
carbonyl compounds, see: (a) Gooßen, L. J.; Rodríguez, N.;
Gooßen, K. Angew. Chem. Int. Ed. 2008, 47, 3100. (b) Dermenci,
A.; Dong, G. Sci. China: Chem. 2013, 56, 685. (c) Takise, R.; Muto,
K.; Yamaguchi, J. Chem. Soc. Rev. 2017, 46, 5864. (d) Guo, L.;
Rueping, M. Chem. Eur. J. 2018, 24, 7794. (e) Liu, C.; Szostak, M.
Org. Biomol. Chem. 2018, 16, 7998.
L. Chem. Commun. 2015, 51, 6123. (e) Tian, C.; Gong, L.;
Meggers, E. Chem. Commun. 2016, 52, 4207. (f) Liu, Q.; Wang, C.;
Zhou, H.; Wang, B.; Lv, J.; Cao, L.; Fu, Y. Org. Lett. 2018, 20, 971.
(g) Zhang, Y.-M.; Yuan, M.-L.; Liu, W.-P.; Xie, J.-H.; Zhou, Q.-L.
Org. Lett. 2018, 20, 4486.
(
15) (Benzyloxy)benzene (2b); Typical Procedure
An oven-dried sealed tube was charged with [Ir(cod) ](BArF4)
2
(5) (a) Murphy, S. K.; Park, J.-W.; Cruz, F. A.; Dong, V. M. Science
(0.0125 mmol, 5 mol%), (R)-Xyl-BINAP (0.0138 mmol, 5.5 mol%),
2015, 347, 56. (b) Souillart, L.; Cramer, N. Chem. Rev. 2015, 115,
and anhyd THF (1.0 mL) under N , and the mixture was stirred
at r.t. for 30 min. 2-(Phenoxymethyl)benzaldehyde (1b; 0.25
2
9410.
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Georg Thieme Verlag Stuttgart · New York — Synlett 2019, 30, A–E

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T. Shirai et al.
Letter
mmol) was added and the resultant mixture was heated at 135 °C
for 24 h with stirring. The mixture was then purified by column
chromatography (silica gel, hexane) to give a colorless liquid;
the mixture was stirred at r.t. for 30 min. Benzaldehyde 1j (0.25
mmol) was added and the mixture was at 90 °C for 48 h with
1
stirring. The formation of lactone (3) was confirmed by H NMR
yield: 16.1 mg (35%).
H NMR (400 MHz, CDCl ):  = 7.27–7.45 (m, 7 H), 6.96–7.00 (m,
spectroscopy, and the conversion (57%) was determined
1
1
through H NMR integration by comparison with the substrate
3
1
3
H), 5.07 (s, 3 H).
peak. H NMR (400 MHz, CDCl ):  = 7.91 (d, J = 7.6 Hz, 1 H), 7.68
3
3
-Methyl-2-benzofuran-1(3H)-one (3)
(td, J = 7.6, 1.2 Hz, 1 H), 7.53 (t, J = 7.6 Hz, 1 H), 7.44 (dd, J = 8.0,
1.2 Hz, 1 H), 5.57 (q, J = 6.8 Hz, 1 H), 1.65 (d, J = 6.4 Hz, 3 H).
(16) Kosaka, M.; Sekiguchi, S.; Naito, J.; Uemura, M.; Kuwahara, S.;
Watanabe, M.; Harada, N.; Hiroi, K. Chirality 2005, 17, 218.
An oven-dried two-necked flask with a condenser was charged
with [Ir(cod) ](BAr 4) (0.0125 mmol, 5 mol%), (R)-Xyl-BINAP
F
2
(0.0138 mmol, 5.5 mol%), and anhyd THF (1.0 mL) under N , and
2
©
Georg Thieme Verlag Stuttgart · New York — Synlett 2019, 30, A–E