Rhodium-catalyzed cyclization reactions of γ-alkynyl aldehydes with carboxylic acid anhydrides

Article abstract of DOI:10.1002/ejoc.201300734

It has been established that a cationic rhodium(I)/H₈-binap or binap complex catalyzes two different modes of cyclization of γ-alkynyl aldehydes with carboxylic acid anhydrides to give cyclic aldehyde gem-dicarboxylates and cyclic alkenyl ester

Full text of DOI:10.1002/ejoc.201300734

SHORT COMMUNICATION
DOI: 10.1002/ejoc.201300734
Rhodium-Catalyzed Cyclization Reactions of γ-Alkynyl Aldehydes with
Carboxylic Acid Anhydrides
Yuki Tajima,[a] Masayuki Kobayashi,[a] Keiichi Noguchi,[b] and Ken Tanaka*[a,c]
Keywords: Aldehydes / Alkynes / Anhydrides / Homogeneous catalysis / Rhodium
It has been established that a cationic rhodium(I)/H8-binap
or binap complex catalyzes two different modes of cyclization
of γ-alkynyl aldehydes with carboxylic acid anhydrides to
give cyclic aldehyde gem-dicarboxylates and cyclic alkenyl
esters through cleavage of the carboxylic acid anhydride C–
O bond. The reaction of a terminal γ-alkynyl aldehyde with
diethyl pyrocarbonate afforded a cyclic allylic carbonate with
a high ee value.
dride,[9,10] although the chelation mode of the carboxylic
acid anhydride to rhodium would be different from that of
the acyl phosphonate (six- vs. five-membered chelation,
Scheme 1). Unexpectedly, we found that the use of carbox-
ylic acid anhydrides in place of heteroatom-substituted
acetaldehydes or acyl phosphonates promoted different
modes of cyclization reactions. Herein, we disclose the rho-
dium-catalyzed cyclization reactions of γ-alkynyl aldehydes
with carboxylic acid anhydrides to produce cyclic allylic
gem-dicarboxylates and cyclic dienyl esters through cleavage
of the carboxylic acid anhydride C–O bond.
Introduction
A number of transition-metal-catalyzed cyclization reac-
tions of γ-alkynyl aldehydes via oxametallacycle inter-
mediates have been developed for the stereoselective synthe-
sis of cyclic allylic alcohol derivatives.[1–6] For example, the
titanium-,[3] nickel-,[4] rhodium-,[5] and ruthenium-cata-
lyzed[6] cyclization reactions of γ-alkynyl aldehydes were
accomplished by using organozincs,[4a] alkenylzirconi-
ums,[4d] organosilanes,[4b,4c,4e,4h,4i,4k–4m,5a,5b] organobor-
anes,[4f,4g,4h,4j] dihydrogen,[5c,5d] and formic acid.[6] Recently,
our research group reported the cationic rhodium(I)/
H8-binap [H8-binap
=
2,2Ј-bis(diphenylphosphanyl)-
5,5Ј,6,6Ј,7,7Ј,8,8Ј-octahydro-1,1Ј-binaphthyl] complex cata-
lyzed cyclization reaction of γ-alkynyl aldehydes with het-
eroatom-substituted acetaldehydes.[7] In this cyclization re-
action, the heteroatom-substituted acetaldehyde acts as a
reducing agent through cleavage of the aldehyde C–H
bond.[7] Subsequently, we extended the above reaction to
the cyclization of γ-alkynyl aldehydes with an acyl phos-
phonate leading to cyclic allylic ester A through cleavage of
the acyl phosphonate C–P bond via oxarhodacycle interme-
diate
B
bearing the chelating acyl phosphonate
(Scheme 1).[8] We anticipated that the cyclization of the γ-
alkynyl aldehyde with a carboxylic acid anhydride would
proceed to give cyclic allylic ester C through cleavage of the
carboxylic acid anhydride C–O bond via rhodacycle inter-
mediate D bearing the chelating carboxylic acid anhy-
[a] Department of Applied Chemistry, Graduate School of
Engineering, Tokyo University of Agriculture and Technology
Koganei, Tokyo184-8588, Japan
E-mail: tanaka-k@cc.tuat.ac.jp
Scheme 1. Rhodium-catalyzed expected cyclization of γ-alkynyl al-
dehydes with carboxylic acid anhydrides.
Homepage: http://www.tuat.ac.jp/~tanaka-k/
[b] Instrumentation Analysis Center, Tokyo University of
Agriculture and Technology,
Koganei, Tokyo184-8588, Japan
Results and Discussion
We first examined the reaction of tosylamide-linked ter-
minal γ-alkynyl aldehyde 1a with benzoic anhydride (2a) at
[c] JST, ACT-C, 4-1-8 Honcho,
Kawaguchi, Saitama, 332-0012, Japan
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201300734.
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Rh-Catalyzed Cyclization Reactions of γ-Alkynyl Aldehydes
80 °C in the presence of the cationic rhodium(I)/H8-binap
catalyst. Unexpectedly, not cyclic allylic ester C but cyclic
allylic gem-dibenzoate 3aa was obtained in low yield
(Table 1, entry 1). Various biaryl bisphosphane ligands
(Figure 1) were then screened, which revealed that decreas-
ing the dihedral angle of biaryl bisphosphane ligands de-
creased the yield of 3aa (dihedral angles:[11] H8-binap Ͼ
binap Ͼ segphos, yield of 3aa: H8-binap Ͼ binap Ͼ
segphos; Table 1, entries 1–3). Non-biaryl bisphosphane li-
gands were also tested, but 3aa was not obtained at all
(Table 1, entries 4 and 5). Increasing the amount of 2a in-
creased the yield of 3aa (Table 1, entries 6 and 7). This un-
Figure 1. Structures of bisphosphane ligands.
expected structure of 3aa was unambiguously confirmed by γ-alkynyl aldehyde 1d with 2a led to a complex mixture of
X-ray crystallographic analysis.[12] Next, the reaction of in- products (Table 2, entry 3). The use of substituted benzoic
ternal γ-alkynyl aldehyde 1b with 2a was examined. Inter- anhydrides was also examined. The reactions of sterically
estingly, not cyclic allylic gem-dibenzoate 3ba but cyclic di- less-demanding anhydrides 2b and 2c with 1a proceeded in
enyl benzoate 4ba was obtained in good yield (Table 1, en- significantly higher yields (Table 2, entries 4 and 5) than
try 9). Screening of biaryl bisphosphane ligands (Table 1, sterically demanding anhydride 2d (Table 2, entry 6). Inter-
entries 9–11) revealed that the use of binap furnished 4ba estingly, the reaction of 1a with diethyl pyrocarbonate (2e)
in the highest yield (Table 1, entry 10). Contrary to the for- did not afford the expected cyclic allylic gem-dicarbonates
mation of 3aa, increasing the amount of 2a decreased the but instead unexpected cyclic allylic carbonate 5ae with a
yield of 4ba (Table 1, entry 12).
high ee value (Table 2, entry 7). We subsequently explored
the scope of the cyclic dienyl ester synthesis by using the
cationic rhodium(I)/binap catalyst at 80 °C (Table 2, en-
tries 8–20). Tosylamide- (i.e., 1b; Table 2, entry 8), nosyl-
amide- (i.e., 1e; Table 2, entry 9), and malonate-linked (i.e.,
1f; Table 2, entry 10) methyl-substituted γ-alkynyl aldehydes
participated in this reaction. In the reaction of 1f with 2a,
olefin isomerization product 6fa was generated along with
4fa (Table 2, entry 10). The use of substituted benzoic anhy-
drides was also examined. Their electronic and steric nature
appeared to have a small impact on the product yields
(Table 2, entries 11–14). The reactions of 2e with 1b and 1e
afforded expected cyclic dienyl carbonates 4be and 4ee in
good yields (Table 2, entries 15 and 16). The use of substi-
tuted γ-alkynyl aldehydes was next examined. The reactions
of α-methyl and γ-phenyl-substituted γ-alkynyl aldehydes
1g and 1h with 2b proceeded in high yields (Table 2, en-
tries 17 and 18). Ethyl- and butyl-substituted γ-alkynyl al-
dehydes 1i and 1j reacted with 2a to give the corresponding
cyclic dienyl benzoates 4ia and 4ja, respectively, with com-
plete stereoselectivity, although their yields were low
(Table 2, entries 19 and 20).
Table 1. Optimization of reaction conditions for the rhodium-cata-
lyzed cyclization of 1a and 1b with 2a.[a]
Entry
1
Ligand
2a [equiv.] Yield [%][b]
3
4ba
1
2
3
1a
1a
1a
1a
1a
1a
1a
1a
1b
1b
1b
1b
H8-binap
binap
segphos
dppb
1.1
1.1
1.1
1.1
1.1
2.0
3.0
5.0
1.1
1.1
1.1
2.0
3aa / 36
3aa / 33
3aa / 11
3aa / 0
3aa / 0
3aa / 42
3aa / 59
3aa / 37
3ab / 0
3ab / 0
3ab / 0
3ab / 0
–
–
–
–
–
–
–
–
67
73
41
66
4
5[c]
6
dppe
H8-binap
H8-binap
H8-binap
H8-binap
binap
segphos
binap
7
8
9
10
11
12
Scheme 2 depicts a possible mechanism for the formation
of 3, 4, and 5, although this proposal is speculative and a
precise mechanism cannot be concluded at the present
stage.[15] γ-Alkynyl aldehyde 1 reacts with the rhodium(I)
catalyst to afford oxarhodacyclopentene D with chelating
acid anhydride 2. σ-Bond metathesis between the C–O and
Rh–O bonds affords intermediate E.[16] In the case of a ter-
minal γ-alkynyl aldehyde (R1 = H), reductive elimination
[a] Reaction conditions: [Rh(cod)2]BF4 (0.010 mmol, cod = 1,5-cy-
clooctadiene), ligand (0.010 mmol), 1 (0.10 mmol), 2a (0.11–
0.30 mmol), and (CH2Cl)2 (2.0 mL). [b] Isolated yield. [c] [Rh-
(nbd)2]BF4 was used (nbd = 2,5-norbornadiene).
Thus, we explored the scope of the cyclic allylic gem- proceeds to afford diester F, which undergoes rhodium-cat-
dicarboxylate synthesis[13] by using the cationic rhodium(I)/ alyzed acyloxy migration to afford cyclic allylic gem-dicarb-
H8-binap catalyst at 80 °C (Table 2, entries 1–6). Not only oxylate 3. In contrast, if diethyl pyrocarbonate (2e) is em-
a tosylamide-linked terminal γ-alkynyl aldehyde (i.e., 1a; ployed, decarboxylation[17] from intermediate E proceeds to
Table 2, entry 1) but also a readily removable nosylamide- afford intermediate G. β-Hydride elimination affords rho-
linked[14] one (i.e., 1c; Table 2, entry 2) could participate in dium hydride H, and subsequent reductive elimination af-
this reaction. However, the reaction of phenyl-substituted fords cyclic allylic carbonate 5. In the case of an internal
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Y. Tajima, M. Kobayashi, K. Noguchi, K. Tanaka
SHORT COMMUNICATION
Table 2. Rhodium-catalyzed cyclization reactions of γ-alkynyl alde- γ-alkynyl aldehyde (R1 = Me), β-hydride elimination from
hydes 1a–j with carboxylic acid anhydrides 2a–f.[a]
intermediate E proceeds to afford allene I, which undergoes
acyloxy migration to afford cyclic dienyl ester 4. This mi-
gration step might also be catalyzed by the cationic rho-
dium through activation of the allene moiety, as shown in
intermediate J.[18]
Scheme 2. Possible reaction mechanism.
In the mechanism shown in Scheme 2, the chelation of
the acid anhydride to the cationic rhodium may be neces-
sary to promote the reactions. Indeed, the reaction of 1a
with nonchelating cyclic carboxylic acid anhydride 2h did
not afford cross-reaction products including cyclic allylic
gem-dicarboxylate 3ah (Scheme 3).
Scheme 3. Rhodium-catalyzed reaction of 1a with cyclic carboxylic
acid anhydride 2h.
Transformations of the cyclization products were briefly
examined. 2,5-Dihydropyrrole 3aa could be readily aroma-
tized by treatment with DDQ (2,3-dichloro-5,6-dicyano-p-
[a] Reactions were conducted with [Rh(cod)2]BF4 (0.010 mmol),
benzoquinone) to give corresponding pyrrole 7 possessing
H8-binap (entries 1–7) or binap (entries 8–20) (0.010 mmol), 1
the gem-dicarboxylate moiety (Scheme 4).[19]
(0.10 mmol), 2 (0.11–0.30 mmol), and (CH2Cl)2 (2.0 mL) at 80 °C
for 24 h. [b] Isolated yield. [c] Ns = SO2(2-NO2C6H4). [d] At 60 °C
for 40 h. [e] γ-Alkynyl aldehyde 1 (0.20 mmol) and 2a (0.22 mmol)
were used.
Annulated heterocycle libraries, structures of which are
shown in Figure 2, includes antimigratory agents.[20] We
were pleased to find that the rhodium-catalyzed cyclization
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Rh-Catalyzed Cyclization Reactions of γ-Alkynyl Aldehydes
Scheme 4. Aromatization of cyclization product 3aa.
reaction of 1b with 2b leading to diene 4bb and the Diels–
Alder reaction of 4bb with N-phenylmaleimide (8) and tet-
racyanoethylene (9) proceeded in one-pot to give analogous
annulated heterocycles 10bb and 11bb in moderate yields
(Scheme 5). An aliphatic carboxylic acid anhydride [hep-
tanoic anhydride (2g)] could also be employed for the pres-
ent cyclization reaction, while the products 4 could not be
isolated in a pure form due to partial hydrolysis during iso-
lation on a silica gel.[21] Pleasingly, the one-pot reaction in-
volving 2g proceeded to give the corresponding stable annu-
lated heterocycle 10bg in moderate yield (Scheme 5).
Scheme 6. One-pot reaction of (Ϯ)-1h with 2b through kinetic reso-
lution.
Conclusions
In conclusion, we have established that a cationic rhodi-
um(I)/H8-binap or binap complex catalyzes two different
modes of cyclization of γ-alkynyl aldehydes with carboxylic
acid anhydrides to give cyclic allylic gem-dicarboxylates and
cyclic dienyl esters through cleavage of the carboxylic acid
anhydride C–O bond. In contrast, the reaction of a terminal
γ-alkynyl aldehyde with diethyl pyrocarbonate afforded a
cyclic allylic carbonate with a high ee value. Future studies
will focus on further utilization of chelating carbonyl com-
pounds for this process.
Figure 2. Annulated heterocycle libraries including antimigratory
agents.
Experimental Section
Representative Procedure for the Rh-Catalyzed Cyclization Reac-
tions of Terminal γ-Alkynyl Aldehydes with Carboxylic Acid Anhy-
drides: H8-binap (6.3 mg, 0.010 mmol) and [Rh(cod)2]BF4 (4.1 mg,
0.010 mmol) were dissolved in CH2Cl2 (2.0 mL), and the mixture
was stirred at room temperature for 10 min. H2 was introduced
to the resulting solution in a Schlenk tube. After stirring at room
temperature for 45 min, the resulting mixture was concentrated to
dryness. To a solution of the residue in (CH2Cl)2 (0.5 mL) was
added a solution of 1a (25.1 mg, 0.100 mmol) and 2a (67.9 mg,
0.300 mmol) in (CH2Cl)2 (1.5 mL). The mixture was stirred at
80 °C for 24 h. The resulting solution was concentrated and puri-
fied by preparative TLC (hexane/EtOAc/toluene = 6:1:2), which
furnished 3aa (28.2 mg, 0.0591 mmol, 59% yield; Table 2, entry 1)
as a colorless oil.
Representative Procedure for the Rh-Catalyzed Cyclization Reac-
tions of Internal γ-Alkynyl Aldehydes with Carboxylic Acid Anhy-
drides: The binap ligand (6.2 mg, 0.010 mmol) and [Rh(cod)2]BF4
(4.1 mg, 0.010 mmol) were dissolved in CH2Cl2 (2.0 mL), and the
mixture was stirred at room temperature for 10 min. H2 was intro-
duced to the resulting solution in a Schlenk tube. After stirring at
room temperature for 45 min, the resulting mixture was concen-
trated to dryness. To a solution of the residue in (CH2Cl)2 (0.5 mL)
was added a solution of 1b (26.5 mg, 0.100 mmol) and 2a (24.9 mg,
0.110 mmol) in (CH2Cl)2 (1.5 mL). The mixture was stirred at
80 °C for 24 h. The resulting solution was concentrated and puri-
fied by preparative TLC (EtOAc/toluene = 1:5), which furnished
4ba (28.7 mg, 0.0733 mmol, 73% yield; Table 2, entry 8) as a color-
less oil.
Scheme 5. One-pot rhodium-catalyzed cyclization and Diels–Alder
reaction.
Finally, kinetic resolution of racemic γ-substituted alk-
ynal 1h with 2b followed by a Diels–Alder reaction with 8
proceeded by using the [Rh(cod)2]BF4/(R)-binap catalyst to
give corresponding enantioenriched annulated heterocycle
(–)-10hb with a moderate ee value (Scheme 6).
Supporting Information (see footnote on the first page of this arti-
cle): Experimental procedures, characterization data, and copies of
1
the H NMR and 13C NMR spectra.
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Y. Tajima, M. Kobayashi, K. Noguchi, K. Tanaka
SHORT COMMUNICATION
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Acknowledgments
This work was supported partly by the Ministry of Education, Cul-
ture, Sports, Science and Technology (MEXT), Japan through
Grants-in-Aid for Scientific Research (grant numbers 25105714,
23105512, and 20675002) and by the Japan Science and Technology
Agency (JST), Japan through ACT-C. The authors are grateful to
Takasago International Corporation for the gift of H8-binap and
segphos and to Umicore for generous support in supplying the rho-
dium complexes.
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[15] Alternatively, 3 and 4 might be generated from 1 and 2 via
cyclic enal K and enone L. This transformation might be cata-
lyzed by the cationic rhodium or HBF4, which can be generated
in situ owing to adventitious water. (The HBF4-catalyzed cycli-
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see: J. U. Rhee, M. J. Krische, Org. Lett. 2005, 7, 2493.) How-
ever, the reactions of 1a and 1b with 2a in the presence of
HBF4·OEt2 (1 mol-%) at 80 °C for 24 h did not afford 3aa and
4ba at all (Ͻ5% conv. of 1a and 1b). As already shown in our
previous report, the reactions of 1a and 1b in the presence of
the cationic rhodium(I)/H8-binap or binap catalyst at room
temperature afford dimers of 1a and 1b through the formation
of the corresponding oxarhodacyclopentene intermediates (see
ref.[7,8]).
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hydroacylation of alkenes with carboxylic acid anhydrides was
reported, see: a) K. Kokubo, M. Miura, M. Nomura, Organo-
metallics 1995, 14, 4521; b) Y.-T. Hong, A. Barchuk, M. J.
Krische, Angew. Chem. 2006, 118, 7039; Angew. Chem. Int. Ed.
2006, 45, 6885.
Furthermore, the reactions of benzaldehyde and acetophenone
with 2a in the presence of the cationic rhodium(I)/H8-binap or
binap catalyst at 80 °C for 24 h did not afford the correspond-
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Eur. J. Org. Chem. 2013, 5266–5271

Rh-Catalyzed Cyclization Reactions of γ-Alkynyl Aldehydes
ing gem-dicarboxylate and enol ester at all. (The Lewis acid
mediated gem-dicarboxylate synthesis from aldehydes was re-
ported, see: K. S. Kochhar, B. S. Bal, R. P. Deshpande, S. N.
Rajadhyaksha, H. W. Pinnick, J. Org. Chem. 1983, 48, 1765).
Chem. 2011, 76, 3024; c) S. Mochida, K. Hirano, T. Satoh, M.
Miura, Org. Lett. 2010, 12, 5776; d) Z.-M. Sun, J. Zhang, P.
Zhao, Org. Lett. 2010, 12, 992; e) E. J. L. Stoffman, D. L. J.
Clive, Org. Biomol. Chem. 2009, 7, 4862; f) Z.-M. Sun, P. Zhao,
Angew. Chem. 2009, 121, 6854; Angew. Chem. Int. Ed. 2009,
48, 6726; g) H. Hara, M. Hirano, K. Tanaka, Org. Lett. 2009,
11, 1337.
[18] In the cationic rhodium(I)/binap complex catalyzed cyclization
of naphthol-linked 1,6-enynes, a mechanism involving cycliza-
tion of allenol through allene activation with the cationic rho-
dium was proposed, see: a) N. Sakiyama, K. Noguchi, K.
Tanaka, Angew. Chem. 2012, 124, 6078; Angew. Chem. Int. Ed.
2012, 51, 5976. The gold-catalyzed cyclization of propargyl es-
ters to produce benzopyrans through allene intermediates was
also reported, see: b) Y.-M. Wang, C. N. Kuzniewski, V. Rauni-
yar, C. Hoong, F. D. Toste, J. Am. Chem. Soc. 2011, 133, 12972.
[19] For examples of the synthetic use of heteroaromatic gem-di-
carboxylates, see: a) H. Gilman, R. R. Burtner, J. Am. Chem.
Soc. 1933, 55, 2903; b) K. Haynes, J. Am. Chem. Soc. 1949,
71, 2581; c) R. Sureshbabu, V. Saravanan, V. Dhayalan, A. K.
Mohanakrishnan, Eur. J. Org. Chem. 2011, 922.
[20] Z. Wang, S. Castellano, S. S. Kinderman, C. E. Argueta, A. B.
Beshir, G. Fenteany, O. Kwon, Chem. Eur. J. 2011, 17, 649.
The marked ligand effects (Table 1) and enantioinduction
(Table 2, entry 7; Scheme 6) also excluded the mechanism via
cyclic enal K and enone L.
[16] In the nickel-catalyzed cyclization with the use of organosil-
anes, Montgomery proposed that the reaction proceeds
through σ-bond metathesis of the organosilane Si–H bond and
the Ni–O bond of the oxanickelacyclopentene intermediate; see
ref.[4k] In the rhodium-catalyzed cyclization with the use of di-
hydrogen, Krische proposed that the reaction proceeds through
σ-bond metathesis of the dihydrogen H–H bond and the Rh–
O bond of the oxarhodacyclopentene intermediate, see ref.[5c]
[17] For recent examples of the rhodium-catalyzed decarboxylation
process, see: a) K. Zhang, J. Louie, J. Org. Chem. 2011, 76,
4686; b) S. Mochida, K. Hirano, T. Satoh, M. Miura, J. Org.
[21] The reaction of 1a with 2g afforded cyclic allylic gem-dibenzo-
ate 3ag, although this product could not be isolated in a pure
form.
Received: May 18, 2013
Published Online: July 12, 2013
Eur. J. Org. Chem. 2013, 5266–5271
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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