Rh-Catalyzed [5+1] and [4+1] cycloaddition reactions of 1,4-enyne esters with co: A shortcut to functionalized resorcinols and cyclopentenones

Article abstract of DOI:10.1002/chem.201200045

We have developed novel Rh-catalyzed [n+1]-type cycloadditions of 1,4-enyne esters, which involve an acyloxy migration as a key step. The efficient preparation of functionalized resorcinols, including biaryl derivatives, from readily available 1,4-enyne esters and CO was achieved by Rh-catalyzed [5+1] cycloaddition accompanied by 1,2-acyloxy migration. When enyne esters had an internal alkyne moiety, the reaction proceeded by a [4+1]-type cycloaddition involving 1,3-acyloxy migration, leading to cyclopentenones.

Full text of DOI:10.1002/chem.201200045

FULL PAPER
DOI: 10.1002/chem.201200045
Rh-Catalyzed [5+1] and [4+1] Cycloaddition Reactions of 1,4-Enyne Esters
with CO: A Shortcut to Functionalized Resorcinols and Cyclopentenones
Takahide Fukuyama,*[a] Yuko Ohta,[a] Cꢀlia Brancour,[a] Kazusa Miyagawa,[a]
Ilhyong Ryu,*[a] Anne-Lise Dhimane,[b] Louis Fensterbank,*[b] and Max Malacria*[b]
Abstract: We have developed novel Rh-catalyzed [n+1]-type cycloadditions of
1,4-enyne esters, which involve an acyloxy migration as a key step. The efficient
preparation of functionalized resorcinols, including biaryl derivatives, from readily
available 1,4-enyne esters and CO was achieved by Rh-catalyzed [5+1] cycloaddi-
tion accompanied by 1,2-acyloxy migration. When enyne esters had an internal
alkyne moiety, the reaction proceeded by a [4+1]-type cycloaddition involving 1,3-
acyloxy migration, leading to cyclopentenones.
Keywords: 1,4-enyne esters
yloxy migration · carbonylation · cy-
cloaddition · rhodium
· ac-
AHCTUNGTRENNUNG
Introduction
bine Rautenstrauch-type reactivity with a carbonylation
event, aiming for a novel [5+1] cycloaddition[8] that could
lead to resorcinols 2 (Scheme 1, pathway a). While the de-
velopment of catalytic processes that lead to phenols and
Connecting an alkene to an alkyne and submitting the cor-
responding 1,n-enyne to a catalytic amount of a transition
metal has led to tremendous developments in organic syn-
thesis, providing access to a wide variety of carbo- and het-
erocyclic systems.[1] While the most studied systems are 1,6-
enynes, 1,5- and 1,4-enynes have also shown versatile re-
ACHTUNGTRENNUNGactivity patterns, particularly when flanked with an O-acyl
group at the propargylic position and in the presence of
electrophilic metal complexes.[2] For example, the well-
known Rautenstrauch rearrangement,[3] which originally
consists of the PdII- or the PtII-catalyzed rearrangement of 1-
ethynyl-2-propenyl acetates 1 to give cyclopentadienyl ace-
tates by 1,2-acyloxy migration, has recently lent itself to val-
uable variations—most notably that of gold catalysis.[4]
From a general perspective, the introduction of intermo-
lecular reactions, such as carbonylations[5] and other incor-
porations,[6] in enyne cyclization processes greatly expands
the scope and value of these reactions, as demonstrated by
recent examples of metal-catalyzed multicomponent cyclo-
additions.[7] In this context, it appeared appealing to com-
Scheme 1. Two types of cyclocarbonylations of 1,4-enyne esters.
their congeners remains an important topic in organic syn-
thesis,[9,10] resorcinols are particularly valuable compounds
with important bioactivity,[11] demonstrating, for instance, ef-
ficient DNA cleavage properties under oxidative conditions,
as well as antibacterial activities.[12] We confirmed the validi-
ty of this synthetic route by using enyne acetates 1 and rho-
dium(I) catalysis.[13] It is worth noting that Tang and co-
workers recently devised versatile rhodium(I)-catalyzed se-
quences, relying on the trapping of Rautenstrauch-type in-
termediates with CO[14] and alkynes.[15]
[a] Prof. T. Fukuyama, Y. Ohta, Dr. C. Brancour, K. Miyagawa,
Prof. I. Ryu
Department of Chemistry, Graduate School of Science
Osaka Prefecture University, Sakai, Osaka 599-8531 (Japan)
Fax : (+81)72-254-9695
E-mail: fukuyama@c.s.osakafu-u.ac.jp
ryu@c.s.osakafu-u.ac.jp
Herein, we give a full account of the [5+1] transformation
that gives access to aromatic substrates 2 from acyclic pre-
cursors 1 with a monosubstituted alkyne moiety (R’=H).
We also report the related [4+1] cycloaddition of disubsti-
tuted alkynes 1 (R’=alkyl), leading to cyclopentenones 3,
based on an initial 1,3-acyloxy migration (Scheme 1, path-
way b).[16,17]
[b] Dr. A.-L. Dhimane, Prof. L. Fensterbank, Prof. M. Malacria
UPMC Univ. Paris 6
Institut Parisien de Chimie Molꢀculaire CNRS
UMR 7201, 4 Place Jussieu, C. 229, 75005 Paris (France)
E-mail: louis.fensterbank@upmc.fr
max.malacria@upmc.fr
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201200045.
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Results and Discussion
tronic effects of substituents on the aromatic ring; thus,
functional groups, such as trifluoromethyl (entry 3) and me-
thoxy groups (entry 4), could be implemented. Enynes 1e
and f with ortho-substituted phenyl groups also worked well
to give the corresponding aryl substituted resorcinols 2e and
f in good yields (entries 5 and 6). 4-Methyl and 3-methyl-
substituted enynes 1g and h gave methyl-phenyl-substituted
resorcinols 2g and h, respectively (entries 7 and 8). In the
case of 1h, a mixture of E/Z isomers (1:0.22) was used.
However, it turned out that the Z isomer was not reactive
towards the carbonylative cyclization (see below for a ratio-
We started our study with 1a as a model substrate to obtain
4-phenyl-substituted resorcinol derivative 2a. Initial at-
tempts with platinum and gold salts did not lead to the car-
bonylation adduct, but to 3-phenylcyclopentenone[18] in vari-
ous yields. We then examined the reaction by using rhodium
catalysts. When the reaction was carried out in the presence
of [RhClACHTUNGTRENNUNG(PPh3)3] under 50 atm of CO in CH2Cl2 at 808C for
5 h, no carbonylation product was obtained (Table 1,
AHCTUNGTRENNUNG
Table 1. Rh-catalyzed [5+1] cycloaddition of enyne ester 1a with CO
leading to resorcinol derivative 2a.[a]
ent catalytic system was tolerant and comparable in reactivi-
ty to 1-ethynyl-2-propenyl pivalates bearing alkyl chains.
Me, nBu, and iPr substitution of the alkene terminus al-
lowed the formation of the desired products in 58 to 74%
yield (entries 9–11). Enyne 1l with a cyclohexene moiety
gave tetrahydronaphthalene derivative 2l (entry 12). The re-
action of enyne 1m with no substituents on the alkene ter-
minus gave the corresponding resorcinol 2m in moderate
yield, which can lead to the natural product olivetol[19]
(entry 13). In this case, the formation of noncarbonylated
cyclopentenone competed.
Entry Catalyst
Solvent
CO [atm] Yield [%][b]
1
2
N
E
CH2Cl2
CH2Cl2
CH2Cl2
50
50
50
50
50
50
50
50
n.r.
traces
30
28
40
66
51
45
3
G
U
4
N
N
5
A
CH2Cl2
CH2Cl2
CH2Cl2
toluene
6
A
7
N
U
We next investigated an enyne ester with an alkyl sub-
stituent on the alkyne terminus. Interestingly, it was found
8
A
9
A
ClCH2CH2Cl 50
50
that a [4+1] cycloaddition reaction,[20] involving a 1,3
ACHTUNGTRENNUNGacyloxy
10
11
12
U
CHCl3
CH2Cl2
CH2Cl2
50
20
80
complex mixture
41
76
migration, took place to give cyclopentenone 3 and isomer-
ized product 3’, in which resorcinol derivative 2 was not
formed (Scheme 2).
[a] Reactions were performed on a 0.5 mmol scale with substrate 1a
(0.05m) for 5 h at 808C. [b] Isolated yields after flash chromatography on
SiO2; cod=1,5-cyclooctadiene; n.r.=not rationalized.
entry 1). The reaction with [Rh6(CO)16] gave only a trace
amount of the desired resorcinol 2a through the [5+1] cy-
cloaddition reaction. With [Rh2ACHTUNGTRNNEUG(OAc)4], [Rh2AHCUTNGTRENN(UGN OCOCF3)4],
and [{RhCl2Cp*}2] (Cp*=1,2,3,4,5-pentamethylcyclopenta-
dienyl), the resorcinol 2a was obtained in moderate yields,
while the conversion was insufficient and 3-phenylcyclopen-
tenone was formed as a by-product (entries 3–5). The yield
of 2a increased with the [{RhCl(CO)2}2] catalyst (entry 6).
When the reaction was carried out by using toluene and di-
chloroethane as solvent, the yield of 2a slightly decreased
(entries 8 and 9), whereas the reaction by using CHCl3 gave
a complex mixture (entry 10). While the reaction under
80 atm of CO gave 2a in 76% yield (entry 12), the carbony-
lated product 2a was obtained in moderate yield under
20 atm of CO, in which a significant amount of unidentified
polymeric materials were formed as by-products (entry 11).
After determining the optimal reaction conditions, we set
out to define the scope of the present [5+1]-type resorcinol
synthesis (Table 2). The cyclization process was also success-
ful when the ester group was changed from pivalate to ace-
tate (entry 2), whereas alcohol (R4 =H), silyl ether (R4 =
TBDMS), and benzyl ether (R4 =CH2Ph) failed to react
with CO. The reaction was compatible with varying elec-
Scheme 2.
The reaction of enyne 1n with CO gave cyclopentenone
3a, which was formed by a [4+1] cycloaddition, and isomer-
ized 3a’ (E/Z=19:81) in 67% total yield (3a/3a’=54:46;
Table 3, entry 1). While the reaction under a higher temper-
ature gave similar results, the yields decreased under
a lower temperature (entries 2 and 3). A similar result was
obtained at 60 atm of CO (entry 4). The reaction was com-
plete after 3 h to give 72% total yield of cyclopentenones
(entry 5). The use of [{RhClACHTNUTRGENNG(U cod)}2] resulted in slightly
better yields of cyclopentenones 3a and 3a’ (entry 6). In this
reaction, conjugated enyne esters by 1,3-acyloxy shift onto
an alkene moiety were also formed as by-products.
A variety of enynes with an alkyl substituent on the
alkyne terminus were examined, and the results are sum-
marized in Table 4. Benzoyl ester and acetate also worked
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Rh-Catalyzed [5+1] and [4+1] Cycloaddition Reactions
FULL PAPER
Table 2.
ACHTUNGTRENNUNG[RhCl(CO)2]2-catalyzed synthesis of functionalized resorcinol derivatives by
tuted enynes, because the Rautenstrauch rearrange-
ment competed in the case of methyl-substituted
enynes.
[5+1] cycloaddition.[a]
Possible mechanisms for the present [5+1] and
[4+1] cycloaddition reactions are shown in
Scheme 3. We postulate that the reaction is initiated
by electrophilic activation of the alkyne moiety of
1 by the rhodium catalyst, leading to p-complex
A.[21] For terminal alkynes, nucleophilic attack of an
ester group occurs to generate a zwitterionic vinyl-
rhodium species B, which undergoes 1,2-acyloxy mi-
gration[22] to give rhodium carbenoid C. The re-
Entry Enyne 1
Resorcinol 2
Yield
[%][b]
1
2
1a R=Piv
1b R=Ac
2a 76
2b 67
3
4
1c R=CF3
1d
R=OMe
2c 56
2d 56
AHCTUNGTRENNGaUN ction with CO to give ketene D and subsequent
6p-electrocyclization[23] gives the transient inter-
mediate E, which undergoes aromatization leading
to 2.[24] However, 1,3-acyloxy migration precedes
this process in the case of internal alkynes,[22] in
which the zwitterionic vinyl-rhodium species F is
converted to rhodacyclopentadiene F. Successive
carbonyl insertion and reductive elimination gives
cyclopentenone 3. An alternative path for cyclopen-
tenone 3 includes the formation of vinyl allenes and
subsequent oxidative cyclization that leads to G.[25]
It is worth noting that when the carbonylation of
1d was carried out in the presence of MeOH
(20 equiv), a low yield of methyl ester 4 was ob-
tained together with resorcinol derivative 2d
(Scheme 4). Formation of 4 would originate from
the nucleophilic trapping of ketene D.
5[c]
6[c]
1e R=Me
1 f R=OMe
2e 67
2 f 61
7
8
1g
2g 53
1h
E/Z (1:0.22)
2h 68[d]
9
1i
1j
2i 58
2j 64
10
Conclusion
11
1k
2k 74
We have developed novel Rh-catalyzed [n+1]-type
cycloadditions of 1,4-enyne esters, involving acyloxy
migration as a key step. The efficient preparation of
functionalized resorcinols, including biaryl deriva-
tives, from readily available 1,4-enyne esters and
CO was achieved by Rh-catalyzed [5+1] cycloaddi-
tion accompanied by 1,2-acyloxy migration. When
enyne esters had an internal alkyne moiety, the re-
action proceeded by [4+1]-type cycloaddition in-
volving 1,3-acyloxy migration, leading to cyclopen-
tenones. Further studies of this reaction toward
target-oriented synthesis are underway in our labo-
ratories.
12
1l
2l 58
2m 37
13[e]
1m
[a] Reactions were performed on a 0.5 mmol scale in dichloromethane (0.05–0.016m)
at 80 atm of CO, except for entry 8 (50 atm). [b] Isolated yields after flash chromatog-
raphy on SiO2. [c] [{RhCl
time: 15 h.
ACHTUNGTERN(NGNU cod)}2] was used. [d] NMR yield of E isomer. [e] Reaction
to give the corresponding cyclopentenones 3b and c and
their isomers (entries 2 and 3). Butyl-substituted enynes 1q
and r could be used for the present [4+1] cycloaddition re-
action (entries 4 and 5). Enynes 1s and t with an isopropyl
substituent on the alkene moiety gave the corresponding cy-
clopentanones (entries 6 and 7). Unlike the [5+1] cycloaddi-
tion reaction, an enyne with no substituents on the alkene
terminus worked in the [4+1] reaction (entries 8–10). Bicy-
clic ketones 3k and l were obtained from enynes 1x and y,
respectively. Generally, enynes with longer alkyl chains gave
higher yields of cyclopentenones compared to methyl-substi-
Experimental Section
Typical procedure for the rhodium-catalyzed carbonylative cyclization of
1,4-enyne esters: A magnetic stir bar, (E)-1-phenyl-1-penten-4-yn-3-yl
pivalate (1a, 128.5 mg, 0.53 mmol), [RhCl(CO)2]2 (4.9 mg, 0.013 mmol)
and CH2Cl2 (10 mL) were placed in a 50 mL stainless steel autoclave.
The autoclave was closed, purged three times with carbon monoxide,
pressurized with carbon monoxide (80 atm), and then heated at 808C for
5 h. Excess of CO was discharged at room temperature. The autoclave
was washed with ether and solvents were removed under reduced pres-
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T. Fukuyama, I. Ryu, L. Fensterbank, M. Malacria et al.
Table 3. Rh-catalyzed [4+1] cycloaddition of enyne ester 1n with CO Table 4. Rh-catalyzed [4+1] cycloaddition of enyne esters with CO leading to cyclo-
leading to cyclopentenones 3a and 3a’.[a]
pentenones.[a]
Entry Enyne 1
3 (E/Z)
3ꢁ (E/Z)
Total yield
[%][b] (3/3’)
Entry Rh catalyst
Temp. CO Time Total
[8C] ACTUHGNTRNEN[UG atm] [h] yield
3a/3a’ (E/
Z)[c]
1[c]
76% (46:54)
[%][b]
1n
3a
3b
3c
3d
3e
3 f
3g
3aꢁ (21:79)
3bꢁ (17:83)
3cꢁ (8:92)
3dꢁ (18:82)
3eꢁ (6:94)
3 fꢁ (18:82)
3gꢁ (15:85)
1
2
3
4
5
6
N
80
80
80
60
60
60
5
5
5
5
3
3
67
41
65
66
72
76
54:46 (19:81)
63:37 (20:80)
58:42 (19:81)
53:47 (19:81)
49:51 (19:81)
46:54 (21:79)
2
51% (41:59)
49% (43:57)
63% (46:54)
57% (38:62)
49% (43:57)
63% (68:32)
1o
ACHTUNGTRENNUNG
[a] Reactions were performed on a 0.5 mmol scale with substrate 1n
(0.05m). [b] Isolated yields after flash chromatography on SiO2. [c] Deter-
mined by H NMR spectroscopy of a crude reaction mixture.
3
1
1p
4[c,d]
1q
5
1r
6
1s
7
1t
8
50% (84:16)
75% (79:21)
84% (93:7)
1u
3h (35:65)
3i (56:44)
3hꢁ (18:82)
3iꢁ (12:88)
9
1v
Scheme 3. Possible mechanisms for Rh-catalyzed [5+1] and [4+1] cyclo-
addition reactions.
10
1w
3j (42:58)
3k (65:35)
3l (44:56)
3jꢁ (14:86)
11[d]
38% (68:32)
73% (75:25)
1x
3k’
3l’
12
1y
[a] Reactions were performed on a 0.5 mmol scale in dichloromethane (0.05m) at
60 atm of CO. [b] Isolated yields. [c] Reaction time: 3 h. [d] [{RhCl(CO)2}2] was used.
Scheme 4.
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Rh-Catalyzed [5+1] and [4+1] Cycloaddition Reactions
FULL PAPER
sure to give the crude reaction mixture (135 mg) as a brown oil. The resi-
due was then purified by short flash chromatography on SiO2 (Et2O/
hexane 3:7) to give 3a as an orange solid (108.7 mg, 76%).
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Acknowledgements
This work was supported by a Grant-in-Aid for Scientific Research on
Innovative Areas (No. 2105) from MEXT Japan and Grant-in-Aid for
Scientific Research (B) from JSPS. This work was supported by CNRS,
IUF (L.F., M.M.), UPMC, and OPU. C.B. gratefully acknowledges
MRES, UPMC, Le Collꢂge Doctoral France–Japon, and OPU.
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[10] For catalytic synthesis of phenol derivatives based on carbonylative
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[7a].
[21] In the case of (Z)-1h, a p-coordinated intermediate might be diffi-
cult to be formed, because the phenyl group blocks the rhodium cat-
alyst to approach to the alkyne moiety. Probably for this reason, the
Z-isomer of 1h would not be reactive towards the present carbony-
lative cyclization. Such observation with a Z-olefin has also been
made by Toste, see ref. [4].
[22] For dual behavior of 1,2/1,3-acetoxy migration with PtCl2, see: a) K.
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[23] For examples of stoichiometric reactions of metal carbenoids with
CO leading to ketenes, see: a) W. A. Herrmann, J. Plank, Angew.
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[24] A similar mechanism was proposed in the Dçtz reaction; for re-
views, see: a) K. H. Dçtz, P. Tomuschat, Chem. Soc. Rev. 1999, 28,
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[25] For Rh-catalyzed [4+1] cycloaddition of vinylallenes, see ref. [20b]
and [20c].
Received: January 5, 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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T. Fukuyama, I. Ryu, L. Fensterbank, M. Malacria et al.
Cycloaddition Reactions
T. Fukuyama,* Y. Ohta, C. Brancour,
K. Miyagawa, I. Ryu,* A.-L. Dhimane,
L. Fensterbank,*
M. Malacria* .................. &&&& — &&&&
Rh-Catalyzed [5+1] and [4+1] Cyclo-
addition Reactions of 1,4-Enyne Esters
with CO: A Shortcut to Functionalized
Resorcinols and Cyclopentenones
Rhodium-catalyzed carbonylation:
New carbonylative cycloaddition re-
AHCTUNGTRENGNaUN ctions of enyne esters have been
developed by using a Rh complex as
the catalyst. The reaction of terminal
alkynes with CO gave functionalized
resorcinols by [5+1] cycloaddition
acompanied by 1,2-acyloxy migration,
whereas internal alkynes gave cyclo-
pentenones by [4+1] cycloaddition
involving 1,3-acyloxy migration (see
scheme).
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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!