Rhodium-catalyzed cascade reactions of dienynes leading to substituted dihydronaphthalenes and naphthalenes

Article abstract of DOI:10.1002/anie.201202125

Five in one: Catalytic cascade reactions of dienynes catalyzed by cationic rhodium(I)-binap complexes lead to the formation of 1,2-dihydronaphthalenes, naphthalenes, and 1,4-dihydronaphthalenes. These cascade reactions involve up to five fundamentally different transformations, including the catalytic enantioselective carboformylation of alkenes with aldehydes or the cycloisomerization of enallenes. Copyright

Full text of DOI:10.1002/anie.201202125

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Angewandte
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DOI: 10.1002/anie.201202125
Cascade Reactions
Rhodium-Catalyzed Cascade Reactions of Dienynes Leading to
Substituted Dihydronaphthalenes and Naphthalenes**
Eri Okazaki, Ryuichi Okamoto, Yu Shibata, Keiichi Noguchi, and Ken Tanaka*
The elimination of a number of reaction steps, the avoidance
of toxic reagents, and the reduction of hazardous waste are
important subjects in modern organic synthesis.[1] To solve
these problems, the development of novel cascade reactions,
in which multiple reactions proceed in one step to afford
complex molecules, is attractive. Obviously, the development
of catalytic versions is even more attractive, and the use of
a single multifunctional catalyst that is able to catalyze
multiple fundamentally different transformations is ulti-
mately desired. We recently reported cascade reactions
catalyzed by a cationic rhodium(I)/dppf complex, including
the olefin isomerization,[2] the propargyl Claisen rearrange-
ment,[3] and the carbonyl migration reaction,[4] which trans-
Scheme 1. Previously reported olefin isomerization/propargyl Claisen
rearrangement/carbonyl migration cascade of an enyne.
form allyl propargyl ethers to allenic aldehydes and dien-
als.[5–7] In these cascade reactions, the single multifunctional
cationic rhodium(I)/dppf catalyst sequentially activates the
[9,10]
allylic[8] and aldehyde C H bonds,
and the alkyne
ether 2. We anticipated that as a result of the chelation of the
styrene moiety to the cationic rhodium core, the subsequent
carbonyl migration would furnish (Z)-dienal 4 as a major
stereoisomer. (Z)-Dienal 4 would be further transformed into
an alkene hydroacylation or related reaction product
(Scheme 2). Herein, we disclose cascade reactions of dienynes
catalyzed by the cationic rhodium(I) complex, involving up to
five fundamentally different transformations, including the
enantioselective carboformylation of alkenes with alde-
hydes[14] or the cycloisomerization of enallenes.
À
p bond.[11,12] In the reaction of an enyne that possesses
a
phenyl-substituted alkene moiety, the corresponding
dienal was obtained in high yield as a mixture of stereoiso-
mers (Scheme 1).
The above-mentioned cascade reactions involve up to
three fundamentally different reactions. We anticipated that if
an allyl propargyl ether possessed an additional olefin moiety,
the novel cascade reaction, which involves more than three
different reaction steps, would succeed. Thus, we designed
dienyne 1, which can be readily synthesized by Grignard
reaction of commercially available 2-bromostyrene and
propargyl alcohol,[13] followed by etherification with a sub-
stituted propargyl alcohol. The olefin isomerization and the
propargyl Claisen rearrangement of dienyne 1 by the cationic
rhodium(I) catalyst would furnish allenic aldehyde 3 via enol
[*] E. Okazaki, R. Okamoto, Y. Shibata, Prof. Dr. K. Tanaka
Department of Applied Chemistry
Graduate School of Engineering
Tokyo University of Agriculture and Technology
Koganei, Tokyo 184-8588 (Japan)
E-mail: tanaka-k@cc.tuat.ac.jp
Homepage: http://www.tuat.ac.jp/~tanaka-k/
Prof. Dr. K. Noguchi
Instrumentation Analysis Center
Tokyo University of Agriculture and Technology
Koganei, Tokyo 184-8588 (Japan)
[**] This work was supported partly by Grants-in-Aid for Scientific
Research (Nos. 20675002 and 23105512) from MEXT (Japan). We
thank Takasago International Corporation for the gift of the ligands
xyl-binap, tol-binap, H8-binap, segphos, and dtbm-segphos, and
Umicore for generous support in supplying a rhodium complex.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201202125.
Scheme 2. Design of the rhodium-catalyzed cascade reaction of dien-
yne 1.
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Table 1: Optimization of reaction conditions.
Entry
Ligand
Conditions
Conversion
[%]
Yield[b]
5a or 6a and/or 7a
2a (E/Z)
3a
1
2
3
dppf
dppf
(R)-binap
(R)-binap
(R)-H8-binap
(R)-segphos
(R)-dtbm-segphos
(R)-tol-binap
(R)-xyl-binap
(S)-dtbm-binap
(R)-xyl-binap
(R)-xyl-binap
RT, 16 h
808C, 16 h
808C, 40 h
408C, 36 h
408C, 36 h
408C, 36 h
408C, 36 h
408C, 36 h
408C, 36 h
408C, 36 h
708C, 24 h
808C, 40 h
100
100
100
100
100
98
78
97
97
19
71%[c] (1.7:1)
<1%
–
–
<1%
–
–
5a: <5%, 7a: 7%
–
–
7a: 34%[c] (51% ee)
4[a]
5[a]
6[a]
7
6a+7a: 49%[c] (6a/7a=12:1, 6a: 76% ee)
37% (1:45)
18% (1:4)
51% (1:8)
7% (1:3)
11% (1:3)
5% (<1:>99)
4% (2:1)
–
<1%
7%
6a: 9%[c] (79% ee)
6a+7a: 26%[c] (6a/7a=12:1, 6a: 60% ee)
16%[c]
4%
–
8[a]
9[a]
10
11[a]
12
6a+7a: 38%[c] (6a/7a=18:1, 6a: 57% ee)
6a: 31%[c] (85% ee)
–
17%[c]
2%
96
100
<1%
–
6a: 45%[c] (80% ee)
7a: 43%[c] (67% ee)
[a] The crude reaction mixture containing aldehyde 5a was treated with NaBH4 (THF/MeOH, RT, 1 h) in order to isolate reduced alcohol 6a.
[b] Determined by 1H NMR spectroscopy. [c] Yield of isolated product.
The reaction of dienyne 1a in the presence of the cationic
rhodium(I)/dppf catalyst was investigated first. At room
temperature olefin isomerization product 2a was generated in
high yield (Table 1, entry 1), on the other hand, at 808C 1,2-
dihydronaphthalene 5a and naphthalene 7a were generated
in low yields (entry 2). The use of (R)-binap as a ligand
furnished 7a in significantly improved yield with a moderate
ee value (Table 1, entry 3). We anticipated that 7a was
generated through the rhodium-catalyzed carbonyl ene
reaction of aldehyde 5a and thus lowered the reaction
temperature to restrain this reaction. Pleasingly, when the
reaction was conducted at 408C for 24 hours, we obtained
alcohol 6a in moderate yield with good ee value after
treatment with NaBH4 (Table 1, entry 4). Thus, we screened
various biaryl bisphosphine ligands (Scheme 3) at 408C
reaction was conducted at 708C for 24 hours to afford alcohol
6a in improved yield with a high ee value (Table 1, entry 11),
and alcohol 7a could also be obtained in moderate yield with
a good ee value by conducting the reaction at 808C for
40 hours (entry 12).
Thus, the scope of the enantioselective 1,2-dihydronaph-
thalene synthesis was explored by using the cationic rho-
dium(I)/(R)-xyl-binap catalyst (Table 2).[15–17] Electronically
diverse aryl groups could be incorporated at the alkyne
terminus to give 1,2-dihydronaphthalenes 6a–f in moderate
yields with high ee values (Table 2, entries 1–6). As the
ee value of 6d was low (49% ee) when the reaction of 1d
was performed at 708C, the reaction was conducted at 408C
for 72 hours (Table 2, entry 4). Interestingly, the ee value of
meta-substituted phenyl derivative 6 f (Table 2, entry 6) was
significantly higher than that of para-substituted phenyl
derivative 6b (entry 2). A primary alkyl group could also be
incorporated at the alkyne terminus by using (R)-binap as
a ligand, although lower enantioselectivity was observed
(Table 2, entry 7). However, the reaction of dienyne 1h,
which possesses a secondary alkyl group at the alkyne
terminus, was sluggish even at 808C, and the ee value of
product 6h was very low (Table 2, entry 8). With respect to
substituents at the propargylic position, the reactions of
acetone- and cycloalkanone-derived tertiary propargyl ethers
1i and 1j proceeded at 408C for 72 hours to give 1,2-
dihydronaphthalenes 6i and 6j, respectively, with high
ee values, although the yields of products decreased
(Table 2, entries 9 and 10).
Scheme 3. Structures of bisphosphine ligands.
(Table 1, entries 5–10) and found that the use of (R)-xyl-
binap furnished 6a with the highest ee value, although the
reaction rate decreased (Table 1, entry 9). Importantly, as the
reactions with some sterically demanding ligands furnished
the expected allene intermediate 3a in isolatable amounts
(Table 1, entries 7 and 9), the structure of 3a was confirmed
unambiguously by its spectral and analytical data. Finally, the
Next, the scope of the enantioselective naphthalene
synthesis was explored at 808C. The reactions of various
substituted arylacetylene-derived dienynes 1a–f proceeded to
give the corresponding naphthalenes 7a–f (Table 2,
entries 11–16), however, the reaction of 4-chlorophenylace-
tylene-derived dienyne 1d was sluggish (Table 2, entry 14)
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Table 2: Asymmetric one-pot synthesis of substituted 1,2-dihydronaphthalenes 6 and naphthalenes 7
from dienynes 1.
aldehyde (+)-5a (78% ee), pre-
pared from 1a by using the cationic
rhodium(I)/(R)-xyl-binap catalyst,
was treated with the cationic rho-
dium(I)/rac-binap
complex
(10 mol%) at 808C. The desired
alcohol (+)-7a was indeed obtained
with almost the same level of chir-
ality transfer as that obtained with
the cationic rhodium(I)/(R)-xyl-
Entry
1 (R1/R2,R2)
Conditions
Yield of 6+7 [%][b]
(6/7)[c]
6 or 7
(% ee)
1[a]
2[a]
3[a]
4[a]
5[a]
6[a]
7[a,d]
8[a,d]
9[a]
10[a]
11
1a (Ph/Me,Me)
708C, 24 h
708C, 24 h
708C, 37 h
408C, 72 h
708C, 38 h
708C, 72 h
608C, 40 h
808C, 96 h
408C, 72 h
408C, 72 h
808C, 40 h
808C, 65 h
808C, 90 h
808C, 90 h
808C, 72 h
808C, 72 h
408C, 25 h;
then 808C, 24 h
45 (6a)
59 (13:1)
58 (13:1)
49 (6d)
47 (7:1)
60 (6 f)
50 (2.3:1)
25[e] (6h)
32 (6i)
(À)-6a (80)
(À)-6b (78)
(À)-6c (77)
(À)-6d (85)
(À)-6e (78)
(À)-6 f (90)
(À)-6g (40)
(À)-6h (12)
(À)-6i (88)
(À)-6j (79)
(+)-7a (67)
(+)-7b (64)
(+)-7c (62)
(S)-(+)-7d (64)
(+)-7e (63)
(+)-7 f (71)
(+)-7g (31)
binap
complex
(68%
ee,
1b (4-F3CC6H4/Me,Me)
1c (4-FC6H4/Me,Me)
1d (4-ClC6H4/Me,Me)
1e (4-MeC6H4/Me,Me)
1 f (3-F3CC6H4/Me,Me)
1g (nBu/Me,Me)
1h (Cy/Me,Me)
1i [Ph/(CH2)4]
1j [Ph/(CH2)5]
1a (Ph/Me,Me)
1b (4-F3CC6H4/Me,Me)
1c (4-FC6H4/Me,Me)
1d (4-ClC6H4/Me,Me)
1e (4-MeC6H4/Me,Me)
1 f (3-F3CC6H4/Me,Me)
1g (nBu/Me,Me)
Scheme 4). Therefore, the chirality
of the rhodium(I) catalyst does not
affect the chirality transfer from 5a
to 7a. On the other hand, treatment
of the same isolated aldehyde 5a
(78% ee) with TiCl4 at 08C fur-
nished bridged pentacyclic alcohol
(+)-8 in moderate yield with an
excellent level of chirality transfer
(Scheme 4). The structure of (Æ)-8
was unambiguously confirmed by
the X-ray crystallographic analysis
(Figure 2).[18] This transformation
represents another synthetic utility
of the present cascade reaction
product.
38 (6j)
43 (7a)
51 (7b)
50 (7c)
31[f] (7d)
29 (7e)
43 (7 f)
40 (7g)
12
13
14
15
16
17[d]
[a] Products were isolated after treatment with NaBH4 (THF/MeOH, RT, 1 h). [b] Yields of isolated
products. [c] Determined by 1H NMR spectroscopy. [d] Ligand: (R)-binap. [e] Alkenyl ether 2h was
obtained in ca. 40% yield. [f] Aldehyde 5d was obtained in ca. 20% yield.
In our previous report, isomer-
ization of allyl propargyl ethers that
possess a secondary propargyl ether
moiety was terminated at the stage
and that of 4-methylphenylacetylene-derived dienyne 1e
afforded the corresponding naphthalene 7e along with
a complex mixture of unidentified products (entry 15). The
reaction of alkylacetylene-derived dienyne 1g could also
furnish naphthalene 7g by using (R)-binap as a ligand,
however, the ee value was low (Table 2, entry 17). With
cycloalkanone-derived substrates 1i and 1j, the carbonyl ene
reaction did not even succeed at 808C. A comparison of
ee values of 1,2-dihydronaphthalenes 6a–g (Table 2, entries
1–7) and naphthalenes 7a–g (entries 11–17) showed that the
present rhodium-catalyzed carbonyl ene reactions are mod-
erately stereoselective. The absolute configuration of naph-
thalene (+)-7d was determined to be (S) by the anomalous
dispersion method (Figure 1).[18,19]
of the corresponding allenic aldehydes.[5] Therefore, the
rhodium-catalyzed reaction of a dienyne that possesses
In order to confirm whether the cationic rhodium(I)
complex catalyzes the carbonyl ene reaction step, the isolated
Scheme 4. Carbonyl ene reaction of isolated 5a with the cationic
rhodium(I)/rac-binap complex versus TiCl4.
Figure 1. ORTEP drawing of (S)-(+)-7d with ellipsoids at 30% proba-
bility.
Figure 2. ORTEP drawing of (Æ)-8 with ellipsoids at 30% probability.
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a secondary propargyl ether moiety would furnish another
product via allenic aldehyde 3 (Scheme 1). Indeed, the
reaction of dienyne 1k in the presence of the cationic
rhodium(I)/rac-binap catalyst at 808C gave vinyl-substituted
1,4-dihydronaphthalene 9k, instead of 1,2-dihydronaphtha-
Table 3: One-pot synthesis of substituted 1,4-dihydronaphthalenes 9
from dienynes 1.[a]
Entry
1
R1
R2
9
Yield[a] [%] (d.r., E/Z)
1
2
3
4
5
6
1k
1l
1m
1n
1o
1p
Ph
H
H
H
H
Me
Ph
9k
9l
9m
9n
9o
9p
76 (1:1, –)
64 (1:1, –)
68 (1:1, –)
42 (1.3:1, –)
61 (2:1, 8:1)
60 (2:1, 7:1)
4-ClC6H4
4-MeOC6H4
nBu
Ph
Ph
[a] Yields of isolated products.
lene, in good yield as a mixture of diastereomers (Table 3,
entry 1). The structure of 9k was confirmed by X-ray
crystallographic analysis (Figure 3).[18] The reactions of both
arylacetylene- and alkylacetylene-derived dienynes 1l–n fur-
nished vinyl-substituted 1,4-dihydronaphthalenes 9l–n in
Figure 3. ORTEP drawing of 9k with ellipsoids at 30% probability.
Scheme 5. Plausible mechanism for the formation of products 5, 7, 8,
and 9 from dienynes 1.
good yields (Table 3, entries 2–4).[15,16] Crotyl- and styryl-
substituted 1,4-dihydronaphthalenes 9o and 9p could also be
obtained in good yields (Table 3, entries 5 and 6).
A plausible mechanism for the present cascade reactions
is outlined in Scheme 5. The olefin isomerization of allyl ether
1 followed by the propargyl Claisen rearrangement furnishes
allenic aldehyde 3 via enol ether 2.[20] In the case of dienynes
that possess a tertiary propargyl ether moiety, the carbonyl
migration reaction proceeds via intermediates B, C, A, and D
to afford rhodium carbonyl hydride E. However, we could not
observe the formation of dienal 4, and so the direct formation
of intermediate E from intermediate C is more likely. In
intermediate E, the styrene and the alkenylrhodium moieties
would predominantly be in Z configuration as a result of the
coordination of the alkene to the rhodium core. The
enantioselective alkene carboformylation proceeds to afford
1,2-dihydronaphthalene 5 via intermediate F. At 808C, the
=
stereoselective carbonyl ene reaction between the exo C C
bond and the formyl group catalyzed by the cationic
rhodium(I) complex[21] further proceeds via chelating inter-
mediate G to generate naphthalene 7. On the other hand, the
carbonyl ene reaction proceeds through sole activation of the
formyl group with TiCl4 to give cationic intermediate H.[22]
The Friedel–Crafts alkylation followed by the methyl group
migration affords 8. We believe that the possible chelation of
rhodium between the alkene moiety and formyl group in
intermediate G may play an important role for the chemo-
selective carbonyl ene reaction of 5a to 7a instead of 8. In the
case of dienyne that possesses a secondary propargyl ether
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2004, 1541; g) S. G. Nelson, C. J. Bungard, K. Wang, J. Am.
Chem. Soc. 2003, 125, 13000; h) J. Le Nꢃtre, L. Brissieux, D.
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moiety, not the carbonyl migration but the enallene cyclo-
isomerization[23] proceeds via rhodacycle I to afford 1,4-
dihydronaphthalene 9.
In conclusion, the catalytic cascade reactions of dienynes,
leading to 1,2-dihydronaphthalenes, naphthalenes, and 1,4-
dihydronaphthalenes, including the catalytic enantioselective
carboformylation of alkenes with aldehydes or the cyclo-
isomerization of enallenes have been developed by using the
cationic rhodium(I)/xyl-binap or binap complex as a catalyst.
It is noteworthy that the present cascade reactions involve up
to five fundamentally different transformations, a goal which
has not been achieved to date. Future studies will focus on
further utilization of the multifunctional cationic rhodium(I)
complex in catalytic cascade reactions.
[7] Recently, novel cascade reactions initiated by the olefin isomer-
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Am. Chem. Soc. 2009, 131, 6354; b) K. Sorimachi, M. Terada, J.
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À
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Espinet, Chem. Eur. J. 2008, 14, 3323; b) K. Tanaka, T. Shoji, M.
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Tani, S. Otsuka, T. Sato, R. Noyori, J. Am. Chem. Soc. 1990, 112,
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Received: March 17, 2012
Published online: May 24, 2012
Keywords: carbonyl ene reactions · cascade reactions ·
.
cycloisomerizations · dienynes · rhodium
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reactions, see: M. C. Willis, Chem. Rev. 2010, 110, 725.
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V. M. Dong, J. Am. Chem. Soc. 2010, 132, 16330; b) D. T. H.
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Soc. 2006, 128, 2782; f) K. Tanaka, G. C. Fu, Chem. Commun.
2002, 684, and references therein. A similar rhodium-catalyzed
isonitrile migration reaction was also reported. See: g) R. T. Yu,
T. Rovis, J. Am. Chem. Soc. 2008, 130, 3262.
[11] For a recent review on transition-metal catalyses through
activation of the alkyne p bond, see: Y. Yamamoto, J. Org.
Chem. 2007, 72, 7817.
[12] For examples of the rhodium(I)-catalyzed Claisen rearrange-
ment through activation of the alkyne p bond, see: a) A. Saito, S.
Oda, H. Fukaya, Y. Hanzawa, J. Org. Chem. 2009, 74, 1517; b) A.
Saito, A. Kanno, Y. Hanzawa, Angew. Chem. 2007, 119, 4005;
Angew. Chem. Int. Ed. 2007, 46, 3931.
[13] J. G. Duboudin, B. Jousseaume, J. Organomet. Chem. 1979, 168,
1.
[14] Although the carboformylation of alkenes with aldehydes has
not been reported, the palladium-catalyzed carboformylation of
alkenes with aryliodides, Ph2Si(Me)H, and CO was reported.
See: S. Brown, S. Clarkson, R. Grigg, W. A. Thomas, V.
Sridharanb, D. M. Wilson, Tetrahedron 2001, 57, 1347.
[15] In the reactions shown in Tables 2 and 3, no major by-product
was obtained. An unidentified complex mixture was generated
instead of the desired products.
[16] Although reactions of 1-naphthyl-substituted dienynes were also
examined, the corresponding products were obtained as a mix-
ture of two or four diastereomers, because of the existence of
axial chirality.
[5] K. Tanaka, E. Okazaki, Y. Shibata, J. Am. Chem. Soc. 2009, 131,
10822.
[6] For selected examples of the sequential olefin isomerization/
Claisen rearrangement of diallyl ethers, see: a) N. J. Kerrigan,
C. J. Bungard, S. G. Nelson, Tetrahedron 2008, 64, 6863; b) K.
Wang, C. J. Bungard, S. G. Nelson, Org. Lett. 2007, 9, 2325;
c) B. M. Trost, T. Zhang, Org. Lett. 2006, 8, 6007; d) S. G. Nelson,
K. Wang, J. Am. Chem. Soc. 2006, 128, 4232; e) C. Nevado, A. M.
Echavarren, Tetrahedron 2004, 60, 9735; f) B. Schmidt, Synlett
6726 www.angewandte.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2012, 51, 6722 –6727

Angewandte
Chemie
data for this paper. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via www.
ccdc.cam.ac.uk/data_request/cif.
[19] Based on the proposed mechanism shown in Scheme 5, the
absolute configuration of (À)-6d is estimated to be (R).
[20] The propargylic ene reaction and cyclization reaction under
thermal conditions have recently been reported, see: a) J. M.
Robinson, T. Sakai, K. Okano, T. Kitawaki, R. L. Danheiser, J.
Am. Chem. Soc. 2010, 132, 11039; b) T. Sakai, R. L. Danheiser, J.
Am. Chem. Soc. 2010, 132, 13203. Therefore, the behavior of
dienyne 1a was examined at 808C in the sole presence of the
phosphine ligand or without additives. In both cases, no reaction
was observed, the rhodium catalyst is thus necessary for the
present cascade reaction.
[21] The rhodium(I)-catalysed hydroformylation of dienes followed
by carbonyl ene reaction was reported. See: R. Roggenbuck, P.
Eilbracht, Tetrahedron Lett. 1999, 40, 7455.
[22] For an example of the TiCl4-mediated carbonyl ene reaction,
see: A. Barbero, C. Garcꢁa, F. J. Pulido, Tetrahedron 2000, 56,
2739.
[23] Few examples of the transition-metal-catalyzed enallene cyclo-
isomerizations were reported. For palladium, see: a) K. Nꢄrhi, J.
Franzꢀn, J.-E. Bꢄckvall, Chem. Eur. J. 2005, 11, 6937. For
ruthenium, see: b) C. Mukai, R. Itoh, Tetrahedron Lett. 2006, 47,
3971. For the palladium-catalyzed carbocyclization of allenic
allylic carboxylates, see: c) J. Franzꢀn, J. Loefstedt, J. Falk, J.-E.
Bꢄckvall, J. Am. Chem. Soc. 2003, 125, 14140. For the palladium-
catalyzed oxidative enallene cycloisomerization, see: d) J. Piera,
K. Naerhi, J.-E. Bꢄckvall, Angew. Chem. 2006, 118, 7068; Angew.
Chem. Int. Ed. 2006, 45, 6914.
[17] The reaction of a-methylstyryl-substituted allyl propargyl ether
was also examined. The reaction rate was low at 708C and
a complex mixture of unidentified products was generated at
808C.
[18] CCDC 809043 ((S)-(+)-7d), CCDC 869802 ((Æ)-8), and
CCDC 809042 (9k) contain the supplementary crystallographic
Angew. Chem. Int. Ed. 2012, 51, 6722 –6727
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
6727