Rhodium-catalyzed linear cross-trimerization of two different alkynes with an alkene and two different alkenes with an alkyne

Article abstract of DOI:10.1002/chem.201200903

Crossing paths with rhodium: A cationic Rh^I/H₈-BINAP complex has been found to catalyze the linear cross-trimerization of terminal alkynes, acetylenedicarboxylates, and acrylamides to give substituted trienes. The asymmetric linear c

Full text of DOI:10.1002/chem.201200903

COMMUNICATION
DOI: 10.1002/chem.201200903
Rhodium-Catalyzed Linear Cross-Trimerization of Two Different Alkynes
with an Alkene and Two Different Alkenes with an Alkyne
Masayuki Kobayashi and Ken Tanaka*[a]
Transition-metal-catalyzed intermolecular linear cross-di-
merization reactions of alkenes with alkynes are efficient
methods for the synthesis of substituted dienes in a highly
atom-economical manner.[1–6] As a more complex transfor-
mation, a few examples of the transition-metal-catalyzed in-
termolecular linear cross-trimerization of two alkynes with
an alkene or two alkenes with an alkyne, leading to substi-
tuted trienes or dienes, respectively, have been reported.[7–10]
The Cheng group first reported the Ni-catalyzed linear
cross-trimerization of two internal alkynes with a,b-unsatu-
rated carbonyl compounds.[7] The related Ni-catalyzed reac-
tions were subsequently reported by the Nakao/Hiyama,[8]
Scheme 1. Transition-metal-catalyzed intermolecular linear cross-trimeri-
zation reactions.
Kurahashi/Matsubara,[9] and Ogoshi[10] groups. The Kuraha-
shi/Matsubara group recently succeeded in performing the
Ni-catalyzed linear cross-trimerization of two acrylates with
internal alkynes.[9,11] However, the transition-metal-catalyzed
intermolecular linear cross-trimerization of two different al-
kynes with alkenes[12] or two different alkenes with alkynes
has not been accomplished previously.[13] Herein, we report
the aforementioned unprecedented selective transformations
by using cationic rhodium(I) complexes as catalysts
(Scheme 1).
Our research group reported the regioselective synthesis
of substituted benzenes through the cationic rhodium(I)/
2,2’-bis(diphenylphosphino)-1,1’-binaphthyl (BINAP) com-
plex catalyzed intermolecular cross-cyclotrimerization of
electron-rich terminal alkynes, acetylenedicarboxylates, and
enol acetates.[14] After this report, we recently reported the
enantioselective construction of bridged multicyclic skele-
tons through the cationic rhodium(I)/(R)-BINAP complex
catalyzed asymmetric intermolecular cross-cyclotrimeriza-
tion of electron-rich terminal alkynes, acetylenedicarboxy-
lates, and enamides, followed by the intramolecular Diels–
Alder reaction.[15] These results prompted us to investigate
the use of electron-deficient acrylates and acrylamides in
place of electron-rich enol acetates and enamides in these
cross-trimerization reactions. Interestingly, the addition of
N-methyl-N-phenylacrylamide (3a), dimethyl acetylenedi-
carboxylate (2a), and phenylacetylene (1a), in that order, to
a
solution of the cationic rhodium(I)/BINAP complex
(10 mol%) in CH2Cl2 at room temperature furnished not
a cross-cyclotrimerization product, but the linear cross-tri-
merization product 4aaa in moderate yield (Table 1,
entry 1). The use of ethyl acrylate instead of acrylamide 3a
furnished no cross-trimerization product.
Table 1. Optimization of reaction conditions for the Rh-catalyzed linear
cross-trimerization of 1a, 2, and 3a.[a]
Ligand
Catalyst 1a
[mol%] [equiv]
2 (R)
4/yield [%][b] (E/Z)
N
ACHTUNGTRENNUNG
1
2
3
4
BINAP
H8-BINAP
SEGPHOS 10
BIPHEP
10
10
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.5
2a (Me)
2a (Me)
2a (Me)
2a (Me)
2a (Me)
2b (Et)
2c (tBu) 4aca/88 (69:31)
2c (tBu) 4aca/82 (72:28)
2c (tBu) 4aca/92 (70:30)
4aaa/45 (73:27)
4aaa/66 (75:25)
4aaa/33 (64:36)
4aaa/24 (60:40)
4aaa/70 (79:21)
4aba/74 (72:28)
10
10
10
10
5
5[c] H8-BINAP
6[c] H8-BINAP
7[c] H8-BINAP
8[c] H8-BINAP
9[c] H8-BINAP
[a] M. Kobayashi, Prof. Dr. K. Tanaka
Department of Applied Chemistry, Graduate School of Engineering
Tokyo University of Agriculture and Technology
Koganei, Tokyo184-8588 (Japan)
5
[a] Reaction conditions: [Rh
diene), ligand (0.010 mmol), 1a (0.11 mmol),
(0.11 mmol), and CH2Cl2 (2.0 mL) were used. [b] Isolated yield based on
2. [c] Reaction conditions: [Rh(cod)2]BF4 (0.010–0.020 mmol), H8-BINAP
ACHTUNGTRENNUNG
Fax : (+81)42-388-7037
E-mail: tanaka-k@cc.tuat.ac.jp
Homepage: http://www.tuat.ac.jp/~tanaka-k/
2
AHCTUNGTRENNUNG
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201200903.
(0.010–0.020 mmol), 1a (0.22–0.30 mmol), 2 (0.20 mmol), 3a (0.22 mmol),
and CH2Cl2 (2.0 mL) were used.
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j, Table 2, entries 10–13) could be employed. Although the
geometry of the product C=C double bond attached to R1
was dependent on the substituents, those attached to the
carbonyl groups were all trans.
The reactions of substituted acrylamides were also exam-
ined, as shown in Scheme 2. Although N,N-dimethylmeth-
Figure 1. Structures of biaryl bisphosphine ligands.
Consequently, various biaryl bisphosphine ligands
(Figure 1) were screened for this reaction (Table 1, en-
tries 1–4), which revealed that the use of H8-BINAP fur-
nished 4aaa in the highest yield (Table 1, entry 2). Screening
of dialkyl acetylenedicarboxylates 2a–c (Table 1, entries 5–
7) in this reaction revealed that the use of di-tert-butyl ace-
tylenedicarboxylate (2c) furnished the corresponding cross-
trimerization product in the highest yield (Table 1, entry 7).
The catalyst loading could be reduced to 5 mol% with only
a slight erosion of the product yield (Table 1, entry 8). Final-
ly, a slight increase in the amount of 1a used in the reaction
further improved the product yield (Table 1, entry 9).
Scheme 2. Rh-catalyzed reactions of 1a, 2c, and substituted acrylamides
3e and f.
acrylamide (3e) failed to react with 1a and 2c, N,N-dimeth-
ylcrotonamide (3 f) was able to react to give the correspond-
ing cross-trimerization product 4acf in moderate yield.
Next, the use of electron-rich monosubstituted alkenes in
place of electron-rich terminal alkynes was attempted. We
were pleased to find that if 3c, 2b, and 1-tetradecene (5a)
were added in that order to a solution of the cationic rho-
dium(I)/(R)-BINAP complex (20 mol%) in CH2Cl2 at room
temperature, and the resulting solution was heated at 408C
for 24 h, linear cross-trimerization product 6abc was formed
in moderate yield with high ee value (Table 3, entry 1). Vari-
ous axially chiral biaryl bisphosphine ligands and acetylene-
dicarboxylates 2a–c were then screened in this reaction
(Table 3, entries 1–5), which revealed that the use of (R)-
BINAP and 2b furnished the cross-trimerization product
with the highest yield and ee value (Table 3, entry 1). More-
over, increasing the amount of 5a improved the product
yield (Table 3, entries 6–9). The optimum catalyst loading
was then examined (Table 3, entries 9–12), which revealed
that the use of 10 mol% of the catalyst retained an accepta-
ble product yield (Table 3, entry 11).
The scope of the reaction towards acrylamides and termi-
nal alkynes is shown in Table 2. With respect to acrylamides,
Table 2. Rh-catalyzed linear cross-trimerization of 1, 2c, and 3.[a]
1 (R1)
3 (R2, R3)
4
Yield [%][b] (E/Z)
1
2
1a (Ph)
1a (Ph)
3a (Ph, Me)
3b (Ph, Ph)
3c (Me, Me)
4aca 92 (70:30)
4acb 84 (78:22)
4acc 87 (40:60)
3[c] 1a (Ph)
4
1a (Ph)
3d (OMe, Me) 4acd 77 (91:9)
5[c] 1b (4-F3CC6H4)
3a (Ph, Me)
3a (Ph, Me)
3a (Ph, Me)
3a (Ph, Me)
4bca 93 (79:21)
4cca 73 (57:43)
4dca 87 (73:27)
4eca 87 (19:81)
6
7
1c (4-MeOC6H4)
1d (4-PhC6H4)
8[c] 1e (2-MeC6H4)
The scope of the reaction towards electron-rich alkenes
and acrylamides is shown in Table 4. With respect to elec-
tron-rich alkenes, various alkyl-substituted alkenes could be
employed for this reaction (Table 4, entries 1–6), but the use
of vinylcyclohexane (5e) decreased both the product yield
and ee value (Table 4, entry 6). Halogen- and oxygen-func-
tionalized alkenes could also be employed (Table 4, en-
tries 7–10). Unfortunately, styrene (5j) failed to participate
in this reaction (Table 4, entry 11). With respect to acryla-
mides, various N,N-dialkylacrylamides (3c, 3g, and 3h;
Table 4, entries 2, 12, and 13) were suitable substrates, but
the use of N-methyl-N-phenylacrylamide (3a) significantly
decreased the product yield (Table 4, entry 14). The product
olefin geometries were all trans, and the absolute configura-
tion of dienamide (+)-6hac was determined to be R by deri-
vatization to the known chiral ketoester.[16] The reactions
with substituted acrylamides 3e and 3 f were tested, proving
that they could not participate in this cross-trimerization re-
action.
9
10
11
12
13
1 f (1-cyclohexenyl) 3a (Ph, Me)
4 fca
83 (50:50)
1g (n-C6H13)
1h [(CH2)2Ph]
1i [(CH2)3Cl]
1j (Cy)
3a (Ph, Me)
3a (Ph, Me)
3a (Ph, Me)
3a (Ph, Me)
4gca 60 (>99:1)
4hca 92 (92:8)
4ica
4jca
75 (95:5)
77 (>99:1)
[a] Reaction
conditions:
[Rh
N
(0.010 mmol),
1 (0.30 mmol), 2c (0.20 mmol), 3 (0.22 mmol), and CH2Cl2 (2.0 mL) were
used. [b] Isolated yield based on 2c. [c] Reaction conditions: [Rh-
ACHTUNGTRENNUNG(cod)2]BF4 (0.020 mmol) and H8-BINAP (0.020 mmol) were used.
not only N-methyl-N-phenylacrylamide (3a, Table 2,
entry 1), but also N,N-diphenylacrylamide (3b, Table 2,
entry 2), N,N-dimethylacrylamide (3c, Table 2, entry 3), and
the Weinreb amide (3d, Table 2, entry 4) could be employed
in this reaction. With respect to terminal alkynes, not only
phenylacetylene (1a, Table 2, entry 1), but also substituted
arylacetylenes (1b–e, Table 2, entries 5–8), an alkenylacety-
lene (1 f, Table 2, entry 9), and various alkylacetylenes (1g–
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Linear Cross-Trimerization Reactions
COMMUNICATION
Table 3. Optimization of reaction conditions for the Rh-catalyzed asymmetric linear
cluding heptatrienamide derivatives, which are diffi-
cult to synthesize by other methods.
cross-trimerization of 5a, 2, and 3c.[a]
Alternatively, these linear products can be readily
transformed into functionalized cyclic compounds.
For example, the trienamides 4 are substituted ben-
zene precursors. Treatment of the E/Z mixture of
4aca with 2,3-dichloro-5,6-dicyano-1,4-benzoqui-
none (DDQ) afforded the corresponding tetrasub-
stituted benzene 7 through an E/Z-isomerization/
dehydrogenation sequence (Scheme 3).[18]
The dienamide 6 is able to participate in the rho-
dium-catalyzed [2+2+2] cycloaddition reaction.[19]
The reaction of (+)-6abc with 1,6-diyne 8 in the
presence of the cationic rhodium(I)/(R)-BINAP
catalyst furnished the densely functionalized chiral
cyclohexadinene (+)-9 as a single diastereomer
(Scheme 4).
Ligand
Catalyst
[mol%]
5a
[equiv]
2 [R]
6/yield [%][b]
(ee [%])
G
G
ACHTUNGTRENNUNG
1
2
3
4
5
6
7
8
(R)-BINAP
(R)-H8-BINAP
(R)-SEGPHOS
(R)-BINAP
(R)-BINAP
(R)-BINAP
(R)-BINAP
(R)-BINAP
(R)-BINAP
(R)-BINAP
(R)-BINAP
(R)-BINAP
20
20
20
20
20
20
20
20
20
15
10
5
1.1
1.1
1.1
1.1
1.1
2
2b (Et)
2b (Et)
2b (Et)
2a (Me)
2c (tBu)
2b (Et)
2b (Et)
2b (Et)
2b (Et)
2b (Et)
2b (Et)
2b (Et)
(+)-6abc/40 (95)
(+)-6abc/25 (91)
(+)-6abc/24 (95)
(+)-6aac/38 (94)
(+)-6acc/13 (86)
(+)-6abc/47 (95)
(+)-6abc/52 (96)
(+)-6abc/54 (95)
(+)-6abc/62 (93)
(+)-6abc/61 (93)
(+)-6abc/55 (93)
(+)-6abc/35 (93)
5
10
9[c]
10[c]
11[c]
12[c]
20 (1.0 mL)
20 (1.0 mL)
20 (1.0 mL)
20 (1.0 mL)
To explain the observed high chemoselectivity,
the reactivity of 1a, 2a–c, 3a,c, and 5b was exam-
ined in the presence of the [Rh
BINAP catalyst at room temperature, as shown in
(cod)2]BF4 (0.010–0.040 mmol), (R)- Scheme 5. Terminal alkyne 1a and internal alkynes
ACHTUGNTNERN(UNG cod)2]BF4/H8-
[a] Reaction conditions: [Rh
2.0 mmol), 2 (0.20 mmol), 3c (0.22 mmol), and CH2Cl2 (2.0 mL) were used. [b] Isolat-
ed yield based on 2. [c] Reaction conditions: [Rh
ACHTUNGTRENN(NUG cod)2]BF4 (0.040 mmol), ligand (0.040 mmol), 5a (0.22–
AHCTUNGTRENNUNG
BINAP (0.010–0.040 mmol), 5a (1.0 mL), 2b (0.20 mmol), 3c (0.22 mmol), and
CH2Cl2 (1.0 mL) were used.
2a,b were spontaneously cyclotrimerized to give the
corresponding substituted benzenes (Scheme 5a
and b),[14] whereas no reaction was observed in the
cases of the sterically demanding internal alkyne 2c
(Scheme 5b), and alkenes 3a,c and 5b (Scheme 5c
and d).
Table 4. Rh-catalyzed asymmetric linear cross-trimerization of 5, 2b, and 3.[a]
Next, cross-reactivity between 1a, 2c, and 3a was
examined in the presence of the [RhACTHNUGRTNE(UNG cod)2]BF4/H8-
BINAP catalyst at room temperature, as shown in
Scheme 6. Terminal alkyne 1a reacted with internal
alkyne 2c to give 10ac (Scheme 6a),[14] whereas 3a
failed to react with both 1a and 2c (Scheme 6b and
c).
5 (R1), [equiv]
3 (R3,R4)
6
Yield[b]
(ee [%])
AHCTUNGTRENNUNG
1
2
5a (n-C12H25), 20 (1.0 mL)
5b (n-C6H13), 32 (1.0 mL)
5b (n-C6H13), 32 (1.0 mL)
5c ((CH2)2Ph), 5
5d (iBu), 40 (1.0 mL)
5e (Cy), 37 (1.0 mL)
5 f ((CH2)4Cl), 5
3c (Me, Me)
3c (Me, Me)
3c (Me, Me)
3c (Me, Me)
3g [(CH2)4]
3c (Me, Me)
3c (Me, Me)
3c (Me, Me)
3c (Me, Me)
3c (Me, Me)
3c (Me, Me)
3g [(CH2)4]
(+)-6abc
(+)-6bbc
(+)-6bac
(+)-6cbc
(À)-6dbg
(+)-6ebc
(+)-6 fbc
(+)-6gbc
(R)-(+)-6hac
(+)-6ibc
6jbc
55 (93)
66 (92)
55 (92)
51 (95)
54 (93)
21 (68)
48 (94)
49 (93)
48 (94)
50 (92)
0
Cross-reactivity between 5b, 2a, and 3a was also
examined in the presence of the [RhACHTUNRTGENUNG(cod)2]BF4/(R)-
3[c]
4
BINAP catalyst at room temperature, as shown in
Scheme 7. One molecule of alkene 5b reacted with
one or two molecules of alkyne 2a to give 11ba
and 12ba (Scheme 7a),[19] whereas 3c failed to react
with both 5b and 2a (Scheme 7b and c). Thus,
acryamide 3 is the least reactive substrate. There-
fore, substrates were added to the catalyst solution
in the order 3, then 2, and finally 1 in Tables 1 and
2, and in the order 3, then 2, and finally 5 in
Tables 3 and 4, although simultaneous addition of
the three substrates did not significantly decrease
the product yields.
5
6[d]
7
8[d]
5g ((CH2)3Br), 5
9[c,d] 5h ((CH2)2CO2Me), 5
10
5i ((CH2)8CO2Me), 22 (1.0 mL)
5j (Ph), 44 (1.0 mL)
5b (n-C6H13), 32 (1.0 mL)
5b (n-C6H13), 32 (1.0 mL)
5b (n-C6H13), 32 (1.0 mL)
11
12
13
14
(+)-6bbg
57 (93)
51 (90)
21 (90)
3h (nBu, nBu) (+)-6bbh
3a (Ph, Me)
(À)-6bba
[a] Reaction conditions: [Rh
(cod)2]BF4/(R)-BINAP (0.020 mmol),
5
(1.0 mL), 2b
(0.20 mmol), 3 (0.22 mmol), and CH2Cl2 (1.0 mL) were used. For entries 4 and 7–9, 5
(1.00 mmol) and CH2Cl2 (2.0 mL) were used. [b] Isolated yield based on 2. [c] 2a was
used instead of 2b. [d] Catalyst: 20 mol%.
A possible reaction pathway for the formation of
trienes 4 is shown in Scheme 8. Alkynes 1 and 2
react with rhodium to generate rhodacyclopenta-
With regard to the synthetic utility of these linear cross-
trimerization reactions, it is important to note that 1,3-buta-
diene-1-carboxamide derivatives, especially 4-alkoxycarbon-
yl-1,3-butadiene-1-carboxamide derivatives, are frequently
found in medicinally important compounds.[17] This method
enables the facile synthesis of interesting new analogues, in-
diene intermediate A. Insertion of acrylamide 3 into inter-
mediate A generates intermediate B. b-Hydride elimination,
followed by reductive elimination and E/Z isomerization,[20]
would furnish triene 4. Indeed, the cross-cyclotrimerization
products 10, formed through intermediate A,[14] were gener-
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K. Tanaka et al.
Scheme 3. Transformation of 4aca into 7.
Scheme 7. Reaction conditions: [RhACHTUNTRGNEUNG(cod)2]BF4/(R)-BINAP catalyst
(10 mol%) in CH2Cl2 at 408C for 24 h (NR=no reaction).
Scheme 4. Reaction of (+)-6abc with 8 to form (+)-9.
Scheme 8. Possible reaction pathways for the reactions of 1, 2, and 3.
Scheme 5. Reaction conditions: [RhCATHUNGTREN(NUNG cod)2]BF4/H8-BINAP catalyst
(5 mol%) in CH2Cl2 at RT for 1 h (NR=no reaction).
Scheme 9. Possible reaction pathways for the reactions of 5, 2, and 3.
tion of acrylamide 3 into intermediate C generates inter-
mediate D. b-Hydride elimination, followed by reductive
elimination, would furnish diene 6. Indeed, the cross-dimeri-
zation and trimerization products 11 and 12, formed through
intermediate C,[19] were generated as byproducts in the reac-
tions presented in Tables 3 and 4.
In conclusion, we have achieved the first catalytic linear
cross-trimerization of two different alkynes with an alkene
and two different alkenes with an alkyne by using the cat-
ionic rhodium(I)/biaryl bisphosphine complexes as catalysts.
Scheme 6. Reaction conditions: [RhACHTNUTRGNEUNG(cod)2]BF4/H8-BINAP catalyst
(5 mol%) in CH2Cl2 at RT for 16 h (NR=no reaction).
ated as byproducts in the reactions presented in Tables 1
and 2.
A possible reaction pathway for the formation of dienes 6
is shown in Scheme 9. Alkene 5 and alkyne 2 react with rho-
dium to generate rhodacyclopentene intermediate C. Inser-
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Linear Cross-Trimerization Reactions
COMMUNICATION
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enantioselectivity. Future work will focus on further explora-
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[8] Y. Nakao, H. Idei, K. S. Kanyiva, T. Hiyama, J. Am. Chem. Soc.
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Acknowledgements
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[11] The Ni-catalyzed intermolecular cross-cyclotrimerization reaction of
two enones with alkynes has been reported. See: ref. [10].
[12] The transition-metal-catalyzed intermolecular cross-cyclotrimeriza-
tion reactions of two different alkynes with alkenes were reported.
For Ni, see: a) N. Mori, S. Ikeda, Y. Sato, J. Am. Chem. Soc. 1999,
121, 2722; b) S. Komagawa, S. Saito, Angew. Chem. 2006, 118, 2506;
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hedron 2009, 65, 5093.
This work was supported partly by a Grant-in-Aid for Scientific Research
(No. 20675002) from MEXT, Japan. We thank Takasago International
Corporation for the gift of H8-BINAP and SEGPHOS, and Umicore for
generous support in supplying a rhodium complex.
Keywords: alkenes · alkynes · asymmetric catalysis · cross-
trimerization · rhodium
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[16] See the Supporting Information for details.
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[18] For examples of the DDQ-mediated aromatization of trienes, see:
a) C. DellꢃErba, A. Gabellini, A. Mugnoli, M. Novi, G. Petrillo, C.
Tavani, Tetrahedron 2001, 57, 9025; b) T. J. Greshock, R. L. Funk, J.
Am. Chem. Soc. 2006, 128, 4946.
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Chem. Soc. Chem. Commun. 1991, 598; b) B. M. Trost, A. Indolese,
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T. J. J. Mꢁller, B. Treptow, J. Am. Chem. Soc. 1995, 117, 615;
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[19] Y. Shibata, K. Noguchi, M. Hirano, K. Tanaka, Org. Lett. 2008, 10,
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[20] K. Tanaka, T. Shoji, M. Hirano, Eur. J. Org. Chem. 2007, 2687.
[5] For Ni, see: H. Horie, I. Koyama, T. Kurahashi, S. Matsubara,
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[6] For Pd, see: a) K. Itoh, K. Hirai, M. Sasaki, Y. Nakamura, H. Nish-
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Received: March 17, 2012
Published online: && &&, 0000
Chem. Eur. J. 2012, 00, 0 – 0
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
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K. Tanaka et al.
Asymmetric Catalysis
M. Kobayashi, K. Tanaka* . &&&& — &&&&
Rhodium-Catalyzed Linear Cross-
Trimerization of Two Different
Alkynes with an Alkene and Two
Different Alkenes with an Alkyne
Crossing paths with rhodium: A cat-
ionic RhI/H8-BINAP complex has been
found to catalyze the linear cross-tri-
merization of terminal alkynes, acety-
lenedicarboxylates, and acrylamides to
give substituted trienes. The asymmet-
ric linear cross-trimerization, giving
substituted chiral dienes, has also been
achieved by using monosubstituted
alkenes and (R)-BINAP instead of ter-
minal alkynes and H8-BINAP (see
scheme; H8-BINAP=2,2’-bis(diphenyl-
phosphino)-5,5’,6,6’,7,7’,8,8’-octahydro-
1,1’-binaphthyl; BINAP=2,2’-bis(di-
phenylphosphino)-1,1’-binaphthyl]).
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www.chemeurj.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!