Cooperative catalytic reactions using organocatalysts and transition metal catalysts: Enantioselective propargylic alkylation of propargylic esters with aldehydes

Article abstract of DOI:10.1021/ol1027865

The enantioselective propargylic alkylation of propargylic esters with aldehydes in the presence of a copper complex and an optically active secondary amine as cocatalysts has been found to give the corresponding propargylic alkylated products in good yields as a mixture of two diastereoisomers with a high enantioselectivity.

Full text of DOI:10.1021/ol1027865

ORGANIC
LETTERS
2011
Vol. 13, No. 4
592–595
Cooperative Catalytic Reactions Using
Organocatalysts and Transition Metal
Catalysts: Enantioselective Propargylic
Alkylation of Propargylic Esters with
Aldehydes
Akiko Yoshida, Masahiro Ikeda, Gaku Hattori, Yoshihiro Miyake, and
Yoshiaki Nishibayashi*
Institute of Engineering Innovation, School of Engineering, The University of Tokyo,
Yayoi, Bunkyo-ku, Tokyo, 113-8656, Japan
ynishiba@sogo.t.u-tokyo.ac.jp
Received November 17, 2010
ABSTRACT
The enantioselective propargylic alkylation of propargylic esters with aldehydes in the presence of a copper complex and an optically active
secondary amine as cocatalysts has been found to give the corresponding propargylic alkylated products in good yields as a mixture of two
diastereoisomers with a high enantioselectivity.
Quite recently, we have found the enantioselective pro-
pargylic alkylation of propargylic alcohols with aldehydes in
the presence of a thiolate-bridged diruthenium complex and
an optically active secondary amine as cocatalysts to give the
corresponding propargylic alkylated products in excellent
yields as a mixture of two diastereoisomers with a high ena-
ntioselectivity (up to 99% ee) (Scheme1).1 This catalytic reac-
tion is considered to provide a new type of enantioselective
propargylic substitution reaction,2 where the enamines gen-
erated in situ from aldehydes enantioselectively attack the
γ-carbon atom of the ruthenium-allenylidene complexes.3
In this reaction system, both the transition metal catalyst
(ruthenium complex) and organocatalyst4 (secondary amine)
(3) For recent reviews of transition metal/allenylidene complexes, see: (a)
Bruneau, C.; Dixneuf, P. H. Angew. Chem., Int. Ed. 2006, 45, 2176. (b) Metal
Vinylidenes and Allenylidenes in Catalysis: From Reactivity to Applications in
Synthesis; Bruneau, C., Dixneuf, P. H., Eds.; Wiley-VCH: Weinheim, 2008. (c)
Cadierno, V.; Gimeno, J. Chem. Rev. 2009, 109, 3512.
(1) Ikeda, M.; Miyake, Y.; Nishibayashi, Y. Angew. Chem., Int. Ed.
2010, 49, 7289.
(4) For recent reviews, see: (a) Asymmetric Organocatalysis; Berkessel,
€
A., Groger, H., Eds.; Wiley-VCH: Weinheim, 2005. (b) Enantioselective
(2) (a) Inada, Y.; Nishibayashi, Y.; Uemura, S. Angew. Chem., Int. Ed.
2005, 44, 7715. (b) Matsuzawa, H.; Miyake, Y.; Nishibayashi, Y. Angew. Chem.,
Int. Ed. 2007, 46, 6488. (c) Matsuzawa, H.; Kanao, K.; Miyake, Y.; Nishibayashi,
Y. Org. Lett. 2007, 9, 5561. (d) Kanao, K.; Matsuzawa, H.; Miyake, Y.;
Nishibayashi, Y. Synthesis 2008, 3869. (e) Kanao, K.; Miyake, Y.; Nishibayashi,
Y. Organometallics 2009, 28, 2920. (f) Fukamizu, K.; Miyake, Y.; Nishibayashi,
Y. J. Am. Chem. Soc. 2008,130, 10498. (g) Kanao, K.; Miyake, Y.; Nishibayashi,
Y. Organometallics 2010, 29, 2126. (h) Kanao, K.; Tanabe, Y.; Miyake, Y.;
Nishibayashi, Y. Organometallics 2010, 29, 2381.
Organocatalysis; Dalko, P. I., Ed.; Wiley-VCH: Weinheim, 2007. (c) Asym-
metric Organocatalysis; List, B., Ed.; Springer: Heidelberg, 2010. (d) Mukher-
jee, S.; Yang, J. W.; Hoffmann, S.; List, B. Chem. Rev. 2007, 107, 5471. (e)
Enders, D.; Grondal, C.; H€uttl, M. R. M. Angew. Chem., Int. Ed. 2007, 46,
1570. (f) Dondoni, A.; Massi, A. Angew. Chem., Int. Ed. 2008, 47, 4638. (g)
Melchiorre, P.; Marigo, M.; Carlone, A.; Bartoli, G. Angew. Chem., Int. Ed.
2008, 47, 6138. (h) MacMillan, D. W. C. Nature 2008, 455, 304. (i) Bertelsen,
S.; Jørgensen, K. A. Chem. Soc. Rev. 2009, 38, 2178. (j) Grondal, C.; Jeanty, M.;
Enders, D. Nat. Chem. 2010, 2, 167.
r
10.1021/ol1027865
Published on Web 01/11/2011
2011 American Chemical Society

Scheme 1
Scheme 2
activate propargylic alcohols and aldehydes, respectively, and
both catalysts cooperatively and simultaneously work to
promote the propargylic alkylation enantioselectively.
On the other hand, we have found the copper-catalyzed
enantioselective propargylic amination of propargylic ace-
tates with amines to give the corresponding propargylic
amines in high yields with a high to excellent enantioselectivity
(up to 98% ee).5-7 The result of the density functional theory
calculation on the model reaction supports the concept that
the catalytic amination proceeds via a copper-allenylidene
complex, where the attack of amines to the γ-carbon atom of
the allenylidene ligand is a key step although the isolation of
copper-allenylidene complexes has not yet been successful.
As an extension of our continuous study on the enantio-
selective propargylic substitution reactions, we have now
envisaged the cooperative catalytic reactions by using both
a copper catalyst and an organocatalyst. In fact, we have
found that reactions of propargylic esters with aldehydes
in the presence of a copper complex bearing racemic
diphosphine and an optically active secondary amine as
cocatalysts give the corresponding propargylic alkylated
products in good yields as a mixture of two diastereoisomers
with a high enantioselectivity. We believe that the method
described in this communication may provide a new type of
dual catalytic reactions using both organocatalysts and tran-
sition metal catalysts.8,9 Preliminary results are described here.
Treatment of 1-(1-naphthyl)-2-propynyl 2,3,4,5,6-penta-
fluorobenzoate (1a) with 3-phenylpropanal (2a) in the pre-
sence of catalytic amounts of (S)-R,R-bis[3,5-bis(trifluoro-
methyl)phenyl]-2-pyrrolidinemethanol trimethyl silyl ether
(3a), a copper trifluoromethanesulfonate-benzene complex,
CuOTf 1/2(C6H6) (10 mol %), and racemic BINAP10 (20
(5) (a) Hattori, G.; Matsuzawa, H.; Miyake, Y.; Nishibayashi, Y.
Angew. Chem., Int. Ed. 2008, 47, 3781. (b) Hattori, G.; Sakata, K.;
Matsuzawa, H.; Tanabe, Y.; Miyake, Y.; Nishibayashi, Y. J. Am. Chem.
Soc. 2010, 132, 10592. (c) Hattori, G.; Yoshida, A.; Miyake, Y.; Nishibayashi,
Y. J. Org. Chem. 2009, 74, 7603. (d) Hattori, G.; Miyake, Y.; Nishibayashi, Y.
ChemCatChem 2010, 2, 155.
(6) (a) Detz, R. J.;Delville, M. M. E.;Hiemstra, H.;vanMaarseveen, J. H.
Angew. Chem., Int. Ed. 2008, 47, 3777. (b) Prof. van Maarseveen and co-workers
achieved the first enantioselective propargylic amination and presented a part of their
result at the PAC-Symposium 2007 (March 1, 2007, Utrecht).
(7) The copper-catalyzed enantioselective propargylic alkylation of
propargylic acetates with enamines was reported by using our reaction
system, where Cl-MeO-BIPHEP and BINAP worked as good chiral
ligands; see: Fang, P.; Hou, X.-L. Org. Lett. 2009, 11, 4612.
(8) For recent reviews, see: (a) Shao, Z.; Zhang, H. Chem. Soc. Rev.
2009, 38, 2745. (b) Klussmann, M. Angew. Chem., Int. Ed. 2009, 48, 7124.
(c) de Armas, P.; Tejedor, D.; García-Tellado, F. Angew. Chem., Int. Ed.
2010, 49, 1013. (d) Zhong, C.; Shi, X. Eur. J. Org. Chem. 2010, 2999. (e)
Rueping, M.; Koenigs, R. M.; Atodiresei, I. Chem.;Eur. J. 2010, 16, 9350.
(9) For recent examples, see: (a) Jellerichs, B. G.; Kong, J.-R.; Krische,
3
mol %) in ClCH2CH2Cl at room temperature for 1.5 h
gave 2-benzyl-3-(1-naphthyl)-4-pentynal (4a) exclusively
(Scheme 2). 2-Benzyl-3-(1-naphthyl)-4-pentyn-1-ol (5a) was
isolated in 53% yield as an inseparable mixture of two
diastereoisomers (syn-5a/anti-5a = 3.2/1) with 98% ee of
syn-5a and 96% ee of anti-5a after the reduction of 4a with
NaBH4 at 0 °C for 1 h. The nature of the ester group in
propargylic esters plays a critical role in promoting the
catalytic alkylation. When the reaction of 1-(1-naphthyl)-2-
propynyl 3,4,5-trifluorobenzoate (1b) was carried out for a
longer reaction time such as 30 h, 5a was obtained in only
19% yield. On the other hand, no propargylic alkylation
occurred at all when 1-(1-naphthyl)-2-propynyl benzoate (1c),
1-(1-naphthyl)-2-propynyl acetate (1d), or 1-(1-naphthyl)-2-
propyn-1-ol was used in place of 1a. Other secondary amines
such as (S)-R,R-diphenyl-2-pyrrolidinemethanol (3b) and
(5S)-2,2,3-trimethyl-5-benzyl-4-imidazolidinone (3c) did not
work at all.
ꢀ
M. J. J. Am. Chem. Soc. 2003, 125, 7758. (b) Ibrahem, I.; Cordova, A. Angew.
Chem., Int. Ed. 2006,45, 1952. (c) Rueping, M.; Antonchick, A. P.; Brinkmann, C.
Angew. Chem., Int. Ed. 2007, 46, 6903. (d) Mukherjee, S.; List, B. J. Am. Chem.
Soc. 2007, 129, 11336. (e) Sorimachi, K.; Terada, M. J. Am. Chem. Soc. 2008,
130, 14452. (f) Usui, I.; Schmidt, S.; Breit, B. Org. Lett. 2009,11, 1453. (g) Terada,
M.; Toda, Y. J. Am. Chem. Soc. 2009, 131, 6354. (h) Li, C.; Villa-Marcos, B.;
Xiao, J. J. Am. Chem. Soc. 2009, 131, 6967. (i) Han, Z.-Y.; Xiao, H.; Chen, X.-H.;
Gong, L.-Z. J. Am. Chem. Soc. 2009, 131, 9182. (j) Lu, Y.; Johnstone, T. C.;
Arndtsen, B. A. J. Am. Chem. Soc. 2009, 131, 11284. (k) Belot, S.; Vogt, K. A.;
Besnard, C.; Krause, N.; Alexakis, A. Angew. Chem., Int. Ed. 2009, 48, 8923. (l)
Zhao, G.-L.; Ullah, F.; Deiana, L.; Lin, S.; Zhang, Q.; Sun, J.; Ibrahem, I.; Dziedzic,
A significantly lower yield of the product was observed
when the amount of 3a was decreased to 10 mol %.
P.; Cordova, A. Chem.;Eur. J. 2010, 16, 1585. (m) Jensen, K. L.; Franke, P. T.;
(10) BINAP=2,20-bis(diphenylphosphino)-1,10-binaphthyl: Noyori,
ꢀ
ꢀ
Arroniz, C.; Kobbelgaard, S.; Jørgensen, K. A. Chem.;Eur. J. 2010, 16, 1750.
R.; Takaya, H. Acc. Chem. Res. 1990, 23, 345.
Org. Lett., Vol. 13, No. 4, 2011
593

Table 1. Copper-Catalyzed Enantioselective Propargylic Alky-
lation of Propargylic Ester (1a) with Aldehydes (2)a
Scheme 3
ee (%)c
time yield of syn-5/
run
R (2)
(h)
5 (%)b anti-5 syn-5 anti-5
1
2
3
4
5
Bn (2a)
1.5 53 (5a) 3.2/1
98
99
97
83
84
96
97
98
94
94
p-ClC6H4CH2 (2b) 1.5 54 (5b) 3.8/1
cHexCH2 (2c)
Me(CH2)4 (2d)
Cl(CH2)4 (2e)
1.5 52 (5c)
58 (5d) 3.5/1
1.5 64 (5e) 3.5/1
3.2/1
2
a All reactions of 1a (0.20 mmol) with aldehyde (2; 0.40 mmol) were
carried out in the presence of CuOTf 1/2C6H6 (0.02 mmol), rac-BINAP
(0.04 mmol), and 3a (0.04 mmol) in ClCH2CH2Cl (5 mL) at room
temperature. b Isolated yield of 5. c Determined by HPLC (see the
Supporting Information for experimental details).
Expectedly, use of ent-3a ((R)-R,R,-bis[3,5-bis(trifluo-
romethyl)phenyl]-2-pyrrolidinemethanol trimethyl silyl
ether) in place of 3a as an organocatalyst gave ent-5a in
59% yield with a similar enantioselectivity. Separately,
we confirmed that the use of only either 3a or the copper
complex did not promote the propargylic alkylation.
This result indicates that both 3a and the copper com-
plex cooperatively worked as catalysts to promote the
catalytic reaction enantioselectively.
Use of an excess amount (20 mol %) of BINAP is neces-
sary to promote the catalytic reaction smoothly (Scheme 3).
The excess amount of BINAP is considered to inhibit
the dissociation of BINAP from the copper atom of the
catalyst. A similar result was achieved when the amounts of a
3
Propargylic alkylation with other aldehydes also
proceeded smoothly to give the corresponding pro-
pargylic alkylated products with a high enantioselec-
tivity. Typical results are shown in Table 1. The reac-
tion of 1a with 3-(4-chloro)phenylpropanal (2b) under
the same reaction conditions gave the corresponding
alkylated product with a similarly high enantioselec-
tivity (Table 1, run 2). When other aldehydes such as
3-cyclohexylpropanal (2c), heptanal (2d), and 6-chloro-
hexanal (2e) were used in place of 3-arylpropanals, the
corresponding propargylic alkyalted products were
obtained in high yields as a mixture of two diastereo-
isomers with a high enantioselectivity (Table 1, runs
3-5). These results indicate that a variety of aldehydes
are suitable for the propargylic alkylation.
It is noteworthy that a higher diastereoselectivity on
the copper-catalyzed propargylic alkylation described
in this paper was achieved than that of the ruthenium-
catalyzed propargylic alkylation1 by using the same
optically active amine as an organocatalyst. However,
unfortunately, the catalytic activity of the copper com-
plex is lower than that of the ruthenium complex
although an excellent enantioselectivity was observed
in both cases.
copper trifluoromethanesulfonate-benzene complex, CuOTf
3
1/2(C6H6) (5 mol %), and racemic BINAP (10 mol %)
were decreased under the same reaction conditions. Inter-
estingly, the stereochemistry of BINAP did not affect the
enantioselectivity of the alkylated product. In fact, a similar
result was achieved when (R)-BINAP or (S)-BINAP was
used in placeof racemic BINAP as a ligand to the copper
complex. Although (R)-Cl-MeO-BIPHEP11 worked as a
suitable ligand for the propargylic alkylation, other diphos-
phines such as racemic BIPHEP,12 (R)-SEGPHOS,13 (R)-
DTBM-SEGPHOS,14 and dppe were not effective ligands.
When the catalytic reaction was carried out in the absence of
diphosphine, a complex mixture was formed with the alky-
lated products.
(11) (R)-Cl-MeO-BIPHEP = (R)-5,50-dichloro-6,60-dimethoxy-2,20-
bis(diphenylphosphino)-1,10-biphenyl: (a) Huddleston,R.R.;Jang,H.-Y.;
Krische, M. J. J. Am. Chem. Soc. 2003, 125, 11488. (b) Jang, H.-Y.; Hughes,
F. W.; Gong, H.; Zhang, J.; Brodbelt, J. S.; Krische, M. J. J. Am. Chem. Soc. 2005,
127, 6174. (c) Rhee, J. U.; Krische, M. J. J. Am. Chem. Soc. 2006, 128, 10674. (d)
Skucas, E.; Kong, J. R.; Krische, M. J. J. Am. Chem. Soc. 2007, 129, 7242.
(12) BIPHEP = 2,20-bis(diphenylphosphino)-1,10-biphenyl: Schmid,
Reactions of other propargylic esters such as 1-(2-naph-
thyl)-2-propynyl (1e), 1-phenyl-2-propynyl (1f), 1-(4-chloro-
phenyl)-2-propynyl (1g), 1-(4-methylphenyl)-2-propynyl
(1h), and 1-(2-methoxyphenyl)-2-propynyl (1i) 2,3,4,5,6-
pentafluorobenzoates with 2a under the same reaction con-
ditions did not proceed smoothly to give the corresponding
propargylic alkylated products in low yields with an excellent
enantioselectivity (not shown).15
€
R.; Foricher, J.; Cereghetti, M.; Schonholzer, P. Helv. Chim. Acta 1991,
74, 370.
(13) (R)-SEGPHOS = (R)-5,50-bis(diphenylphosphino)-4,40-bi-1,3-
benzodioxole: Nagasaki, I.; Matsumura, K.; Sayo, N.; Saito, T. Acc.
Chem. Res. 2007, 40, 1385 and references therein.
A proposed reaction pathway is shown in Scheme 4. The
initial step is the formation of an allenylidene complex (B)
(14) (R)-DTBM-SEGPHOS = (R)-5,50-bis[di(3,5-di-tert-butyl-
4-methoxyphenyl)phosphino]-4,40-bi-1,3-benzodioxole.
594
Org. Lett., Vol. 13, No. 4, 2011

In summary, we have found the enantioselective pro-
pargylic alkylation of propargylic esters with aldehydes
in the presence of a copper complex bearing racemic
BINAP and an optically active secondary amine as
cocatalysts to give the corresponding propargylic alky-
lated products in good yields as a mixture of two
diastereoisomers with a high enantioselectivity (up to
99% ee). This catalytic reaction is considered to provide
a new type of enantioselective propargylic substitu-
tion reaction,16 where the enamines generated in situ
from aldehydes enantioselectively attack the copper-
allenylidene complexes. In the present reaction system,
both the transition metal catalyst (copper complex) and
organocatalyst (secondary amine) activate propargylic
esters and aldehydes, respectively, and both catalysts
cooperatively and simultaneously work to promote the
propargylic alkylation enantioselectively. We believe
that the finding described here will open up a new aspect
of not only dual catalytic reactions using both organo-
catalysts and transition metal catalysts but also the
enantioselective R-alkylation of aldehydes.17,18 Further
work is currently in progress to apply this strategy to
other reaction systems and to clarify the scope and
limitations of the present propargylic alkylation.
Scheme 4
by the reaction of propargylic ester 1 with the copper
complex via an alkyne complex (A). Subsequent attack
of an enamine (E) generated in situ from aldehyde 2 and
amine 3aupon the γ-carbon of B results inthe formation of
another alkyne complex (D) via an acetylide complex (C).
Then, the alkylated product 4 is formed from D by ligand
exchange with another propargylic ester 1. In fact, we
confirmed that no reaction occurred at all when reactions
of propargylic esters bearing an internal alkyne moiety
were carried out under the same reaction conditions. These
results clearly indicate that this propargylic alkylation
proceeded via copper-allenylidene complexes as key and
reactive intermediates.5
Acknowledgment. This work was supported by a Grant-
in-Aid for Scientific Research for Young Scientists (S) (No.
19675002) from the Ministry of Education, Culture, Sports,
Science and Technology, Japan. M.I. acknowledges the
Global COE program for Chemistry Innovation. Y.N.
thanks the Ube Industries LTD.
Supporting Information Available. Experimental pro-
cedures and spectroscopic data. This material is available
free of charge via the Internet at http://pubs.acs.org.
To obtain some information on the enantioselective
propargylic alkylation, the stereochemistry of the product
syn-5a was compared with that of the propargylic alkylated
product which were previously obtained from the reaction of
1-(1-naphthyl)-2-propyn-1-ol with 2a.1 This result indicates
that the absolute configuration of syn-5a is [(2R,3S)]. The
information on the stereochemistry of the propargylic alky-
lated products supports that the asymmetric induction of the
propargylic alkylation catalyzed by the copper complex was
achieved in a similar manner as that by the ruthenium
complex, which was proposed in the previous paper.1 Thus,
for the formation of major products syn-5, enamine, gener-
ated from chiral amine and aldehyde, attacks from the Si-face
of enamine upon the Re-face of the copper-allenylidene
complex leading to the carbon-carbon bond formation.
(16) For recent reviews, see: (a) Nishibayashi, Y.; Uemura, S. Curr.
Org. Chem. 2006, 10, 135. (b) Nishibayashi, Y.; Uemura, S. Comprehensive
Organometallic Chemistry III, Vol. 11; Crabtree, R. H., Mingos, D. M. P.,
Eds.; Elsevier: Amsterdam, 2007; p 123. (c) Kabalka, G. W.; Yao, M.-L.
Curr. Org. Synth. 2008, 5, 28. (d) Ljungdahl, N.; Kann, N. Angew. Chem.,
Int. Ed. 2009, 48, 642. (e) Miyake, Y.; Uemura, S.; Nishibayashi, Y.
ChemCatChem 2009, 1, 342. (f) Detz, R. J.; Hiemstra, H.; van Maarseveen,
J. H. Eur. J. Org. Chem. 2009, 6263.
(17) For a recent review, see: Alba, A.-N.; Viciano, M.; Rios, M.
ChemCatChem 2009, 1, 437.
(18) For recent examples, see: (a) Nicewicz, D. A.; MacMillan,
D. W. C. Science 2008, 322, 77. (b) Shaikh, R. R.; Mazzanti, A.; Petrini,
M.; Bartoli, G.; Melchiorre, P. Angew. Chem., Int. Ed. 2008, 47, 8707. (c)
Cozzi, P. G.; Benfatti, F.; Zoli, L. Angew. Chem., Int. Ed. 2009, 48, 1313. (d)
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10, 4557. (e) Wu, J.; Ni, B.; Headley, A. D. Org. Lett. 2009, 11, 3354. (f)
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Carter, R. G. J. Org. Chem. 2009, 74, 2246. (h) Laars, M.; Ausmees, K.;
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Capdevila, M. G.; Benfatti, F.; Zoli, L.; Stenta, M.; Cozzi, P. G.
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(15) (a) Preliminary results are as follows: For 1e, 27% yield (4.5 h),
syn-isomer/anti-isomer = 1.8/1, 97% ee (syn-isomer) and 96% ee (anti-
isomer). For 1f, 20% yield (4 h), syn-isomer/anti-isomer = 1.7/1, 98% ee
(syn-isomer) and 95% ee (anti-isomer). (b) Unfortunately, some other
propargylic esters bearing an electron-rich aromatic moiety at the
propargylic position such as 1-(4-methoxyphenyl)-2-propynyl (1j) and
1-(4-methoxynaphthyl)-2-propynyl (1k) 2,3,4,5,6-pentafluorobenzoates
could not be prepared from the corresponding propargylic alcohols due
to the instability of the pentafluorobenzoate esters (not shown).
Org. Lett., Vol. 13, No. 4, 2011
595