Rhodium-catalysed alkoxycarbonylative cyclisation reactions of 1,6-enynes

Article abstract of DOI:10.1002/adsc.201000772

The rhodium-catalysed carbonylation of 1,6-enynes possessing an electron-deficient alkenyl moiety in an alcohol reagent in the presence of a rhodium complex proceeded stereo- and chemoselectively to afford exocyclic α,β-enoates.

Full text of DOI:10.1002/adsc.201000772

COMMUNICATIONS
DOI: 10.1002/adsc.201000772
Rhodium-Catalysed Alkoxycarbonylative Cyclisation Reactions of
1,6-Enynes
Fırat Ziyanak,a Melih Kus¸,a and Levent Artoka,*
a
Department of Chemistry, Faculty of Science, Izmir Institute of Technology, Urla 35430, Izmir, Turkey
Fax : (+90)-232-750-7509; phone: (+90)-232-750-7529; e-mail: leventartok@iyte.edu.tr
Received: October 13, 2010; Revised: January 11, 2011; Published online: April 12, 2011
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/adsc.201000772.
Abstract: The rhodium-catalysed carbonylation of
1,6-enynes possessing an electron-deficient alkenyl
moiety in an alcohol reagent in the presence of a
rhodium complex proceeded stereo- and chemose-
lectively to afford exocyclic a,b-enoates.
Scheme 1. Rhodium-promoted double carbonylation of
alkyne.
Keywords: alkoxycarbonylation; cyclisation; a,b-
enoates; 1,6-enynes; five-membered rings; rhodium
of I has also been observed occasionally as a compet-
ing route.[5,7,8b,c]
Alkenylrhodium(I) species, such as I, that can be
The hydroesterification of simple alkynes that forms generated via the addition of several types of rhodium
a,b-unsaturated esters is an extensively studied pro- species, are also reactive leading to carborhodation of
À
cess, which is usually operated over a Pd-based cata- electrophilic sites, effecting C C bond formation.
lyst in the presence of an alcohol reagent.[1] There are Such a formation has been described for a variety of
also a few reported cases in which alkynes were car- cascade-type reactions that construct a functionalised
bonylated in alcohol reagents in the presence of rho- cyclic product.[9]
dium complexes. However, the latter rhodium-cata-
Within this context, we have envisaged that alkynyl
lysed method often resulted in double incorporation reagents bearing another unsaturated moiety in an ap-
of the carbonyl moiety.[2] For example, Mise reported propriate position could also undergo alkoxycarbony-
that the Rh-catalysed carbonylation of internal al- lative cyclisation, thus being analogous to the reac-
kynes in ethanol gave a 5-ethoxy-5H-furan-2-one de- tions of in situ generated organorhodium[9] and Si
À
rivative as the main product.[3] The carbonylation of Rh[10] species with the acceptors bearing two or more
phenyl-substituted acetylenes in the presence of alco- electrophilic sites.
hols was found to form 3-alkoxycarbonylindanones.[4]
To investigate this possibility, a 1,6-enyne (1a)
Chatani reported that the rhodium-catalysed carbony- having an ester functionality on the olefinic site was
lation of internal alkynes with pyridin-2-ylmethanol reacted in MeOH under 10 atm of CO at 1008C in
proceeded through a chelate-assisted transformation the presence of [RhCl
and a double hydroesterification, resulting in 1,4-di- (Table 1, entry 1). This first attempt produced appre-
carboxylate esters.[5]
ciably an ethylidenecyclopentane derivative bearing
ACHTUNGTERN(NNUG cod)]2 (5% Rh) for 16 h
The reactions that utilised nucleophiles other than an ester group on one of the olefinic carbons (3aa) in
alcohols, e.g., water,[6] amines,[7] or organoborons[8] 75% GC yield and the configuration of the olefinic
also resulted in double carbonylation of alkynes with group was assigned by an NOE study (Scheme 2).
rhodium catalysts, leading to cyclised products. The
It must be noted that 1,6-enynes usually undergo a
majority of these rhodium-catalysed carbonylation Pauson–Khand-type reaction leading to cyclopenten-
processes seem to involve the formation of carbony-
ACHTUNGTRENoNGNU nes when subjected to rhodium-catalysed carbonyla-
lated alkenylrhodium(I) species (I) that have a high tion reactions in an unreactive solvent,[11] whereas no
propensity for insertion into CO, giving rise to acyl- traces of cyclopentenone derivatives were detected
ACHTUNGTRENNUNGrhodium species (II) (Scheme 1). Protodemetalation within the product mixture in the present case.
Adv. Synth. Catal. 2011, 353, 897 – 902
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
897

Fırat Ziyanak et al.
COMMUNICATIONS
Scheme 2. Alkoxycarbonylative cyclisation of enyne 1a.
Table 1. Effect of reaction parameters on the rhodium-cata-
lysed methoxycarbonylative cyclisation of 1a.[a]
Table 2. Effect of the nature of the catalyst precursor on the
rhodium-catalysed methoxycarbonylative cyclisation of 1a.[a]
Entry T
PCO
Water
[mg]
Conv.
[%][b]
Yield 3aa
Entry Catalyst
Conv. Yield
[8C] [atm]
[%][b]
[%][b] 3aa [%][b]
1
2
3
4
5
6
7
8
100
100
100
50
10
10
10
10
10
10
5
0
100
100
100
47
75
82
53
24
67
42
68
71
1
2
3
4
5
6
7
8
Rh
[RhCl(CO)2]2
[RhCl(nbd)]2
[RhCl(cod)]2
RhCl3·3H2O
[RhCl(C2H4)2]2
[Rhacac(C2H4)2]2
[RhOH(cod)]2
[Rh(PPh3)3(CO)H]
[RhCl(cod)]2 +20% PPh3
[RhCl(cod)]2 +20% P(OPh)3
[RhCl(cod)]2 +10% dppe
[RhCl(cod)]2 +10% dppp
[RhCl
[RhCl
[RhCl
G
100
100
100
100
100
100
100
100
100
45
78
79
77
82
68
61
45
52
72
23
50
10
31
25
81
70
50
250
50
50
50
50
50
ACHTUNGTRENNUNG
A
E
80
88
120
100
100
100
100
100
E
E
T
15
9
[a]
Reactions were run with 0.3 mmol of 1a and the complex
[RhCl(cod)]2 (5% Rh) in 5 mL of methanol for 16 h.
10
11
12
13
14
15[c]
16[d]
E
E
T
N
R
G
A
ACHTUNGTRENNUNG
N
71
14
65
[b]
Determined by GC.
100
100
The presence of a small amount of water within the
reaction mixture seems beneficial for the formation of
3aa. The presence of 50 mg of water in the reaction
medium caused an increase in the formation of 3aa
(entry 2), but a larger content of water (250 mg) was
detrimental to the selectivity of the process (entry 3).
Whereas increasing the reaction temperature to
1208C reduced the selective formation of the desired
product, owing to the increased formation of intricate
by-products, the conversion of the enyne 1a was not
[a]
Reactions were run with 0.3 mmol of 1a, 50 mg of water,
and 5% of Rh at 1008C under 10 atm of CO pressure in
5 mL of methanol for 16 h.
Determined by GC.
Performed with 10% of Rh.
[b]
[c]
[d]
Performed with 3% of Rh.
complete at the lower reaction temperatures of 508C yield can be obtained even with the non-ligated
and 808C (entries 4–6). The optimum CO pressure RhCl3·3H2O compound (entry 5).
was set at 10 atm; employing either lower or higher
CO pressures than this lessened the opportunity for ed rhodium complex, [Rh
formation of the desired product (entries 7 and 8). to relatively good result (entry 9), the presence of
The activity of various rhodium complexes was also PPh3, P(OPh)3, or bidentate phosphorous ligands
surveyed at the 5% of rhodium loading level greatly reduced the activity of the rhodium catalyst
(Table 2). The complexes, Rh(cod)2BF4, coming from the [RhCl(cod)]2 complex (entries 10–
[RhCl(CO)2]2, [RhCl(nbd)]2, and [RhCl(cod)]2 dis- 14). It was not necessary to use a higher concentration
In contrast with the activity of the phosphine-ligat-
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
A
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
played similarly higher activities compared to the of rhodium, since a comparable result was also ob-
other complexes tested (entries 1–9), the yields being tained at the 10% Rh loading level (entry 15). Yet the
within the range of 77–82% with these complexes (en- yield decreased when using a lower levels of catalyst
tries 1–4). A somewhat lower but still reasonable loading (3% Rh) (entry 16).
898
asc.wiley-vch.de
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2011, 353, 897 – 902

Rhodium-Catalysed Alkoxycarbonylative Cyclisation Reactions of 1,6-Enynes
Table 3. Rhodium-catalysed alkoxycarbonylative reaction of
1a with various alcohols.[a]
group as well as ester and ketone substituents on the
outer olefinic carbon (entries 1–4) providing the cor-
responding methyl 2-(cyclopentenylidene)acetate de-
rivatives in good isolated yields (3ba–3ea). Enyne 1f,
having a trimethylene tether, gave a complex mixture
and consequently, the desired product 3fa was ob-
tained in low yield as determined by H NMR analy-
sis (entry 5).
An oxygen-bridged enyne 1g was also an appropri-
ate substrate, and accordingly converted to a methyl
Entry
ROH
Isolated Yield [%]
1
2
3
4
5
6
MeOH
EtOH
PrOH
BuOH
i-PrOH
allyl alcohol
79 (3aa)
66 (3ab)
64 (3ac)
64 (3ad)
43 (3ae)
54 (3af)
1
[a]
Reactions were run with 0.3 mmol of 1a, 50 mg of water, 2-[dihydrofuran-3
ACHTUNGTERNN(UNG 2H)-ylidene]acetate product 3ga in
and [RhCl
ACHTUNGTRENNUNG(cod)]2 (5% Rh) at 1008C under 10 atm of CO
good yield (entry 6). Interestingly, the presence of a
nitrogen functionality within the structure of enyne as
a linker (1h) or a substituent on the olefinic site (1i
and 1i’), gave rise to hydroesterification products 4 in
pressure in 5 mL of alcohol for 16 h.
Next, we surveyed the scope of the method for var- addition to the formation of the desired products (en-
ious alcohols and enyne reagents under the estab- tries 7–9).
lished reaction conditions, that is at 1008C, 10 atm of
CO, in 5 mL of alcohol containing 50 mg of water ad- ture of E- and Z-isomers. When the substrate contain-
ditive, and using [RhCl(cod)]2 (5% Rh) as the catalyst ing E- and Z-1i isomers in a molar ratio of 3:1 was
It should be noted that the substrate 1i was a mix-
AHCTUNGTRENNUNG
precursor. The carbonylative reaction of 1a with subjected to a carbonylation reaction in methanol, the
MeOH, EtOH, or primary saturated C3 and C4 alco- yields of products 3ia and 4ia were obtained in the
hols all gave rise to the corresponding cyclic products molar ratio 2:1. We also synthesised a cyanoallyl-sub-
in good isolated yields (Table 3, entries 1–4). Moder- stituted, dimethyl malonate-tethered enyne 1i’ in a
ate yields of 3a products could also be obtained with higher E to Z isomeric ratio of 7.3:1 (see the Support-
a bulky alcohol, isopropyl alcohol, or a functionalized ing Information) and conducted a carbonylation reac-
alcohol, allyl alcohol (entries 5 and 6).
tion using this isomeric mixture. It was interesting to
Table 4 includes representative results of the rhodi- find out that the latter substrate afforded 3ia’ and 4ia’
um-catalysed alkoxycarbonylation of various 1,6- in a higher yield ratio (6:1). That the 3:4 ratio of
enynes with methanol. As shown, the method is suita- products is directly related with the E:Z ratio of cya-
ble for enynes having a malonate-based tether bear- noallyl-substituted enyne substrate charged into the
ing an ethyl or CH2OMe substituent on the alkynyl reaction system indicates that the 4ia and 4ia’ by-
Table 4. Rhodium-catalysed methoxycarbonylative reaction of 1,6-enynes.
Entry
X
R
EWG
Isolated Yield [%] 3:4
1
C
C
C
C
CH2
O
N
Et
CH2OMe
Me
Me
Me
Me
Me
Me
Me
CO2Me
CO2Me
COPh
COMe
CO2Et
CO2Et
CO2Me
CN
61:0 (3ba)
62:0 (3ca)
64:0 (3da)
71:0 (3ea)
31:0 (3fa)
68:0 (3ga)
41:14 (3ha)
44:22 (3ia)
54:9 (3ia’)
ND[d] (3ja)
2
3[a]
4
5
6
7
NTs
8[b]
9[c]
10
C
C
C
CN
H
Me
[a]
Performed with 8% of Rh.
[b]
[c]
[d]
The substrate 1i was an isomeric mixture of E and Z in the ratio of 3:1.
The substrate 1i’ was an isomeric mixture of E and Z in the ratio of 7.3/1.
Not determined.
Adv. Synth. Catal. 2011, 353, 897 – 902
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
899

Fırat Ziyanak et al.
COMMUNICATIONS
Scheme 3. Rhodium-catalysed methoxycarbonylation of diethyl 2-(but-2-ynyl)-2-methylmalonate (5a).
Table 5. Rhodium-catalysed hydroesterification of alkynes.
products were mainly formed from the Z-configured
enynes 1i and 1i’, respectively
The methodology is not suitable for the enyne with
an unsubstituted olefinic site (3ja). The carbonylation
reaction of 1ja led to a complex mixture of isomers of
cyclised and non-cyclised methoxycarbonylates with
complete conversion (entry 10).
Entry
R
Isolated Yield [%]
It has been considered that a dual interaction be-
tween substrate and rhodium species facilitates the
1,2-carborhodation step of alkynes and regulates the
regioselectivity of the process.[9,12] To evaluate wheth-
er such a promotive effect can also be legitimate for
the alkoxycarbonylation of alkynes, we conducted an
analogous reaction with the substrate 5a, which lacks
an alkenyl moiety. A regioisomeric hydroesterified
mixture was formed from 5a indicating that coordina-
tion of the alkenyl moiety to rhodium has no signifi-
1[a]
2[b]
3[b]
4[b]
Ph
Ph
Pr
Ph, Me
65 (6ba)
75 (6ba)
73 (6ca)
80 (1:1)[c] (6da)
[a]
Performed under the conditions of Table 4.
Performed with 1 mmol of 5 and 3% of Rh in 10 mL of
2a at 808C.
[b]
[c]
Isomeric ratio.
cant influence on the reactivity of 1 towards alkoxy- and subsequent protodemetalation steps generate the
carbonylation, but rather governed the resulting re- desired cyclised product 3.
gioselectivity with enynes (Scheme 3).
Relatively stronger intramolecular coordination of
The method was also applied on several simple the rhodium with the nitrogen functionality within the
alkynes (Table 5). (E)-Methyl 2,3-diphenylacrylate intermediate B could account for the formation of hy-
(6ba) product was recovered in 65% yield from the droesterification products when reacted with either
reaction of diphenylacetylene in MeOH under the es- the enyne 1h[13] or 1i (Scheme 5). The existence of
tablished conditions for enynes 1 (entry 1). Modifica- such coordinative interactions may obviate the next
tion of experimental conditions which involved a carborhodation step (formation of the intermediate
lower reaction temperature of 808C and catalyst load- C), leading to the protodemetalation hydroesterifica-
ing (3% Rh) with respect to the substrate improved tion products 4ha and 4ia, respectively. It should be
the yield to 75% (entry 2). The method was also suit- noted that such a coordinative interaction should be
able for a dialkylacetylene, 4-octyne, yet not regiose- more achievable with the Z-configured isomer of 1i
lective for hydroesterification of an unsymmetric as compared to E-1i since its spatial arrangement
alkyne, 1-phenylpropyne (entries 3 and 4).
would allow the rhodium and the nitrile group to
The formation of double carbonylative products adopt a closer distance.
was negligible in our case. A double carbonylation
In summary, we have presented within this report
product 5-alkoxy-2(5H)-furanone which was the that rhodium-catalysed carbonylation of 1,6-enynes
major product type of a previous study[3] was deter- with an alkenyl moiety substituted by an electron
mined to be usually less than 3% within the complex withdrawing group in an alcohol constructs five-mem-
by-product mixtures. Probably application of milder bered rings with an exocyclic alkenyl ester group. The
conditions, e.g., lower CO pressure and temperature, method can also be applied on simple internal alkynes
and absence of any base and ligand additives disfav- to construct a,b-unsaturated esters.
oured the double carbonylation path.
In view of the results with enynes and alkynes, the
rhodium-catalysed alkoxycarbonylative cyclisation of
Experimental Section
1,6-enynes should proceed through a carboalkoxyrho-
dium intermediate A,[3] followed by intramolecular cis
Carbonylation Reactions
addition to the triple bond in a regioselective manner
to give the alkenylrhodium(I) B (Scheme 4). Intra-
A mixture of substrate, rhodium complex, and predried and
carborhodation onto the tethered double bond (C) degassed alcohol was added to a 50-mL stainless steel auto-
900
asc.wiley-vch.de
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2011, 353, 897 – 902

Rhodium-Catalysed Alkoxycarbonylative Cyclisation Reactions of 1,6-Enynes
Scheme 4. Reaction mechanism for the alkoxycarbonylation of 1,6-enynes.
References
[1] a) G. Kiss, Chem. Rev. 2001, 101, 3435–3456; b) A.
Brennfꢁhrer, H. Neumann, M. Beller, ChemCatChem
2010, 2, 509–513; c) J. F. Knifton, J. Mol. Catal. 1977, 2,
293–299; d) B. E. Ali, H. Alper, J. Mol. Catal. 1991, 67,
29–33; e) K. Itoh, M. Miura, M. Nomura, Tetrahedron
Lett. 1992, 33, 5369–5372; f) E. I. Drent, P. Arnoldy,
P. H. M. Budzelaar, J. Organomet. Chem. 1993, 455,
247–253; g) M. T. Reetz, R. Demuth, R. Goddard, Tet-
rahedron Lett. 1998, 39, 7089–7092; h) B. E. Ali, J.
Tijani, A. M. El-Ghanam, Tetrahedron Lett. 2001, 42,
2385–2387; i) M. Akao, S. Sugawara, K. Amino, Y.
Inoue, J. Mol. Catal. A: Chem. 2000, 157, 117–122; Pt-
catalysed: j) Y. Tsuji, T. Kondo, Y. Watanabe, J. Mol.
Catal. 1987, 40, 295–304.
Scheme 5. Alkenylrhodium(I) intermediates (C) which may
arise from the enynes 1h and Z-1i.
clave containing a glass insert tube. Then, the sealed auto-
clave was evacuated and purged with 10 atm CO twice, suc-
cessively. Subsequently, the reactor was pressurised with CO
and the mixture was stirred magnetically in a preheated oil
bath. After cooling, the reaction mixture was recovered with
ethyl acetate. The solvent was evaporated and the residue
was purified by flash chromatography (hexane-EtOAc), af-
fording the product.
[2] A. Vizer, K. B. Yerzhanov, A. A. A. A. Quntar, V. M.
Dembitsky, Tetrahedron 2004, 60, 5499–5538.
[3] T. Mise, P. Hong, H. Yamazaki, J. Org. Chem. 1983, 48,
238–242.
[4] E. Yoneda, T. Kaneko, S.-W. Zhang, K. Onitsuka, S.
Takahashi, Tetrahedron Lett. 1999, 40, 7811–7814.
[5] S. Inoue, K. Yokota, H. Tatamidani, Y. Fukumoto, N.
Chatani, Org. Lett. 2006, 8, 2519–2522.
[6] a) K. Doyama, T. Joh, K. Onitsuka, T. Shiohara, S. Ta-
kahashi, J. Chem. Soc. Chem. Commun. 1987, 649–650;
b) T. Joh, K. Doyama, K. Onitsuka, T. Shiohara, S. Ta-
kahashi Organometallics 1991, 10, 2493–2498. A CO-
free hydrocyclocarbonylation process: c) K. Fuji, T.
Morimoto, K. Tsutsumi, K. Kakiuchi, Chem. Commun.
2005, 3295–3297.
Acknowledgements
The support of The Scientific and Technological Research
Council of Turkey (TBAG-108T985), and IZTECH (2009-
IYTE-19) to this work is gratefully acknowledged. We thank
Ms. I. ꢀzÅelik, Mr. S. Gꢁnnaz, and Dr. W. Hiller for NMR
analyses and Dr. H. ꢀzgener for FT-IR analyses, and Dr. R.
Eanes for proof reading.
Adv. Synth. Catal. 2011, 353, 897 – 902
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
901

Fırat Ziyanak et al.
COMMUNICATIONS
[7] S. Inoue, Y. Fukumoto, N. Chatani, J. Org. Chem. 2007,
72, 6588–6590.
[11] T. Shibata, Adv. Synth. Catal. 2006, 348, 2328–2336.
[12] a) R. Shintani, A. Tsurusaki, K. Okamoto, T. Hayashi,
Angew. Chem. 2005, 117, 3977–3980; Angew. Chem.
Int. Ed. 2005, 44, 3909–3912; b) T. Miura, M. Shimada,
M. Murakami, J. Am. Chem. Soc. 2005, 127, 1094–
1095; c) T. Miura, M. Shimada, M. Murakami, Chem.
Asian J. 2006, 1, 868–877.
[13] Sulfonamides can complex with rhodium: a) I. Karamꢄ,
M. Jahjah, A. Messaoudi, M. L. Tommasino, M. Lem-
aire, Tetrahedron: Asymmetry 2004, 15, 1569–1581;
b) N. A. Cortez, R. Rodrꢅguez-Apodaca, G. Aguirre,
M. Parra-Hake, T. Coleb, R. Somanathan, Tetrahedron
Lett. 2006, 47, 8515–8518; c) N. A. Cortez, G. Aguirre,
M. Parra-Hake, R. Somanathan, Tetrahedron: Asymme-
try 2008, 19, 1304–1309.
[8] a) ꢂ. Aksın, N. Dege, L. Artok, H. Tꢁrkmen, B. C¸ etin-
kaya, Chem. Commun. 2006, 3187–3189; b) M. Kus¸, ꢂ.
Aksin-Artok, F. Ziyanak, L. Artok, Synlett 2008, 2587–
2592; c) L. Artok, M. Kus¸, ꢂ. Aksın-Artok, F. N. Dege,
F. Y. ꢂzkılınÅ, Tetrahedron 2009, 65, 9125–9133.
[9] a) T. Miura, M. Murakami, Chem. Commun. 2007,
217–224, and references cited therein; b) S. W. Youn,
Eur. J. Org. Chem. 2009, 2597–2605, and references
cited therein; c) T. Miura, M. Yamauchi, M. Murakami,
Synlett 2007, 2029–2032; d) L. Artok, M. Kus¸, B. N.
ꢃrer, G. Tꢁrkmen, ꢂ. Aksın-Artok, Org. Biomol.
Chem. 2010, 8, 2060–2067; e) M. Lautens, T. Mar-
quardt, J. Org. Chem. 2004, 69, 4607–4614.
[10] a) C. Liu, R. A. Widenhoefer, Organometallics 2002,
21, 5666–5673; b) S. E. Denmark, J. H.-C. Liu, J. Am.
Chem. Soc. 2007, 129, 3737–3744.
902
asc.wiley-vch.de
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2011, 353, 897 – 902