Gold(I)-catalyzed synthesis of (1E,3E)-dienes from propargylic esters

Article abstract of DOI:10.1016/j.jorganchem.2008.08.010

A mild and stereoselective gold(I)-catalyzed domino transformation of propargylic esters leading to substituted (1E,3E)-dienes has been developed. This cascade process proceeds via a sequence of 1,3-acyloxy- or 1,3-phosphatyloxy migrations to form allenic

Full text of DOI:10.1016/j.jorganchem.2008.08.010

Journal of Organometallic Chemistry 694 (2009) 482–485
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Communication
Gold(I)-catalyzed synthesis of (1E,3E)-dienes from propargylic esters
*
Alexander S. Dudnik, Todd Schwier, Vladimir Gevorgyan
Department of Chemistry, University of Illinois at Chicago, 845 West Taylor Street, Chicago, IL 60607-7061, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 24 May 2008
Received in revised form 6 August 2008
Accepted 6 August 2008
Available online 12 August 2008
A mild and stereoselective gold(I)-catalyzed domino transformation of propargylic esters leading to
substituted (1E,3E)-dienes has been developed. This cascade process proceeds via a sequence of 1,3-acyl-
oxy- or 1,3-phosphatyloxy migrations to form allenic intermediate followed by a proton transfer.
Ó 2008 Elsevier B.V. All rights reserved.
Keywords:
Gold
Homogeneous catalysis
Rearrangement
Propargylic esters
1,3-Dienes
1. Introduction
Herein, we wish to report a mild and stereoselective Au(I)-cat-
alyzed 1,3-migration – proton transfer cascade of propargylic es-
During past decade, propargylic esters [1] have received much
attention as a highly valuable building blocks in contemporary or-
ganic chemistry. Intriguing reactivity of these compounds in the
context of gold catalysis [2] has been reflected in the development
of a variety of diverse and elegant cascade transformations.
Remarkable propensity of propargylic esters 1 to undergo a formal
1,3-acyloxy migration [1,2] through the activated allene equiva-
lent, intermediate i [1], allowed for the development of diverse
transformations for the expeditious assembly of an immense array
of complex acyclic molecules [3], and multisubstituted carbo- [4]
and heterocycles [5] (Eq. (1)).
ters 1 into 1-oxy-(1E,3E)-diene esters 2 (Eq. (3)).
R1
H
R3 OXO
Au-cat
rt
H
OXO
R2
R1
E
2
E
1,3-OXO~ /
proton transfer
ð3Þ
R2
R3
1
this work
OXO = OC(O)R, OP(O)(OEt)2
2. Results and discussion
Recently, we reported a Au(I)-catalyzed double 1,3-/1,2-migra-
tion cascade transformation of propargylic esters 1 into functional-
ized naphthalenes and 1,3-dienes (Eq. (4)) [9]. It was proposed that
propargylic esters 1, which are fully substituted at the b-position,
underwent a Au(I)-catalyzed 1,3-acyloxy- or 1,3-phosphatyloxy
group migration to give cyclic intermediate ii (Eq. (4)). The followed
1,2-migration of alkyl- or aryl group (MG = Alk, Ar) [10] in the latter
R1
R1
[M]
"1,3" ~
O
O
O
Various acyclic and
cyclic products
ð1Þ
O
[M]
i
1
Recently, two stereoselective Au(I)-catalyzed isomerizations of
propargylic esters into 2-oxy-1,3-diene esters [6], proceeding via a
1,3-migration – silicon elimination (Eq. (2), route a) [7] or double
1,2-migration (Eq. (2), route b) [8] tandems, were reported by Zhang.
MG
R2
OXO
or
X
X
OXO
H MG
O
O
O
O
2
R1
R2
R2
R1
Au
R2
R1
1,2~
R2
ð4Þ
OC(O)R3
1,3~
Au-cat
rt
R1
iii
[Au]
MG [Au]
MG
MG
1
R1
ii
1,3~ /
E
OC(O)R3
(a)
(b)
Si-elimination
R2 = Me3Si
R1 = Ph
ð2Þ
R1
R2
produced intermediate iii, which, upon subsequent proton loss and
protiodeauration, afforded 1,3-diene or underwent further cycloiso-
merization into the naphthalene core (Eq. (4)). In contrast, it was
found that propargylic ester 1a, possessing a hydrogen atom at
the b-position, was transformed into (1E,3E)-diene 2a via a se-
quence of two formal 1,3-migrations [9] (Eq. (5)).
Au-cat
Z
R2
E
80 o
C
R1
OC(O)R3
1,2-/1,2-H~
* Corresponding author. Tel.: +1 312 355 3579; fax: +1 312 355 0836.
E-mail address: vlad@uic.edu (V. Gevorgyan).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.08.010

A.S. Dudnik et al. / Journal of Organometallic Chemistry 694 (2009) 482–485
483
OP(O)(OEt)2
2.5%
Ph3PAuOTf
H
OP(O)(OEt)2
5 mol%
Ph3PAuOTf
Ph
OP(O)(OEt)2
E
Ph
Ph
1a
•
ð5Þ
OP(O)(OEt)2
86%
86%
Ph
2a
E
0.05M
DCM, rt
3a
1a
Ph
0.05M in
DCM, rt
2a
H
OP(O)(OEt)2
observed by GC-MS and NMR
ð7Þ
It deserves mentioning that the isomerization of acetates 1 into
10% AgOTf
5% Ph3PAuOTf
>99%
1,3-dienes 2 in the presence of Ag-catalysts at elevated tempera-
tures has been reported [11] (Eq. (6)). The cascade reaction was
hypothesized to proceed via the allene intermediate 3, though,
the mechanism of this transformation remained unclear.
DCM, rt
Ph
OP(O)(OEt)2
•
73%
3a
In light of the recent observations that eventual Brønsted acids
are the true catalysts in some transition metal-catalyzed transfor-
mations [12], we investigated what role, if any, Brønsted or Lewis
acids may play in the herein described isomerization reaction. It
was found that isomerization of propargyl phosphate 1a in the pres-
ence of 20 mol% of TfOH or TMSOTf provided no 1,3-diene 2a. In
addition, isomerization of the allene 3a into the corresponding
1,3-diene in the presence of Brønsted or Lewis acids even at ele-
vated temperatures resulted in trace amounts of 2a only (Eq. (8)).
Thus, the observed reactivity for the Au(I) catalyst cannot be attrib-
uted to the eventual Brønsted acid.
R2
H
R2
OAc
OAc
Ag
Δ
Ag
Δ
R1
H
E
ð6Þ
R1
OAc
•
R2
R1
2
1
3
We aimed at elucidating whether the Au(I)-catalyzed isomeriza-
tion of phosphate-containing substrate 1a (MG = H) proceeds via an
allenic intermediate. The performed careful monitoring of the reac-
tion course at early stages revealed that, indeed, the corresponding
allene intermediate 3a was formed and then completely converted
into (1E,3E)-diene 2a (Eq. (7)). In addition, allene 3a, prepared inde-
pendently via the Ag-catalyzed 1,3-migration protocol, in the pres-
ence of cationic Au(I) triflate was quantitatively transformed into
1,3-diene 2a (Eq. (7)).
20% TMSOTf
Ph
Ph
or HOTf
OP(O)(OEt)2
•
OP(O)(OEt)2
traces
ð8Þ
DCE, rt or
Δ
3a
2a
Table 1
R2
H
R3
OXO
R3
2.5 mol%
Ph3PAuOTf
R1
R2
OXO
DCM, rt
R1
H
Entry
Substrate
Product
Yield (%)a
Ph
Ph
1
2
3
4
5
6
7
1a
2a
83
OP(O)(OEt)2
OP(O)(OEt)2
Ph
Ph
OP(O)(OEt)2
OAc
1bb
1c
2b
2c
2d
2e
2f
69c,d
OP(O)(OEt)2
Ph
Ph
79
OAc
OPiv
Ph
Ph
1d
1ee
1f
86
OPiv
OP(O)(OEt)2
75c,f
70
OP(O)(OEt)2
Ph
Ph
OAc
OAc
OP(O)(OEt)2
OP(O)(OEt)2
1g
2g
82g
a
Isolated yield; 0.5 mmol scale.
b
c
d
e
f
12.5:1 mixture of diastereomers.
5 mol% of the Au-catalyst was used.
4.3:1 mixture of (1E,3E):(1E:3Z)-dienes.
1.2:1 mixture of diastereomers.
1.3:1 mixture of (1E,3E):(1E:3Z)-dienes.
7.5 mol% of the Au-catalyst was used.
g

484
A.S. Dudnik et al. / Journal of Organometallic Chemistry 694 (2009) 482–485
Next, we investigated the scope of this reaction. Thus, isomeriza-
3. Conclusions
tion of differently substituted propargylic esters 1a–g was exam-
ined in the presence of Ph3PAuOTf catalyst (Table 1) [13]. It was
found that the cascade transformation of propargylic esters 1a,c,d
possessing various 1,3-migrating groups, such as phosphatyloxy-
(entry 1), acyloxy- (entry 3) and pivaloxy- (entry 4), proceeded
highly stereoselectively to provide good to high yields of (1E,3E)-
dienes 2a,c,d, respectively [14]. b-Dialkyl- (entries 5 and 7), alkyl-
In summary, we developed a mild and stereoselective gold(I)-
catalyzed approach toward multisubstituted (1E,3E)-dienes from
propargylic esters which features tandem sequence of 1,3-migra-
tion and a proton transfer.
Acknowledgment
aryl (entries 2 and 6), as well as b-diaryl- and
a-alkyl- (entry 6)
substituted propargylic esters, were nearly equally efficient in this
transformation, providing corresponding 1,3-dienes 2b,e,f,g in good
to high yields. However, isomerization of phosphates 1b and 1e,
unsymmetrically substituted at the b-position, proceeded with low-
er stereoselectivity (entries 2 and 5).
The support of the National Institutes of Health (Grant GM-
64444) is gratefully acknowledged.
References
We propose the following mechanism for the cascade transfor-
mation of propargyl esters 1 into 1,3-dienes 2 (Scheme 1). The
Au(I)-catalyzed 1,3-migration [15] transforms 1 into a cyclic inter-
mediate iv [1b,3c,5b] which, upon elimination of gold catalyst, fur-
nishes allene intermediate 3. A direct elimination of the proton
from iv gives a vinyl gold intermediate v, which after the protio-
deauration produces 1,3-diene 2 and regenerates the Au(I)-catalyst
(Scheme 1).
[1] (a) For recent reviews, see: J. Marco-Contelles, E. Soriano, Chem. Eur. J. 13
(2007) 1350;
(b) N. Marion, S.P. Nolan, Angew. Chem., Int. Ed. 46 (2007) 2750.
[2] (a) For recent reviews, see: S. Ma, S. Yu, Z. Gu, Angew. Chem., Int. Ed. 45 (2006)
200;
(b) A.S.K. Hashmi, Angew. Chem., Int. Ed. 44 (2005) 6990;
(c) A. Hoffmann-Röder, N. Krause, Org. Biomol. Chem. 3 (2005) 387;
(d) A.M. Echavarren, C. Nevado, Chem. Soc. Rev. 33 (2004) 431;
(e) G. Dyker, Angew. Chem., Int. Ed. 39 (2000) 4237;
(f) A.S.K. Hashmi, Chem. Rev. 107 (2007) 3180;
Exclusive or predominant (1E,3E)-stereoselectivity of the for-
mation of 1,3-diene products 2, observed during the Au(I)-cata-
lyzed cascade isomerization of propargylic esters 1, can be
rationalized by the consideration of the stereoelectronic models
A/B and C/D for the proton elimination and protiodeauration steps,
respectively. Accordingly, proton elimination in cyclic iv occurs
through the conformationally more favorable model A leading to
3E-stereoisomeric v, whereas in the unfavorable model B bulkier
RL experiences repulsion with 1,3-dioxenium moiety (Scheme 2).
Similarly, 1E-configuration in 2 arises from the elimination of
Au(I)-catalyst proceeding exclusively via the conformationally pre-
ferred model C (Scheme 2).
(g) A.S.K. Hashmi, G.J. Hutchings, Angew. Chem., Int. Ed. 45 (2006) 7896;
(h) A. Fürstner, P.W. Davies, Angew. Chem., Int. Ed. 46 (2007) 3410;
(i) Y. Yamamoto, J. Org. Chem. 72 (2007) 7817;
(j) L. Zhang, J. Sun, S.A. Kozmin, Adv. Synth. Catal. 348 (2006) 2271;
(k) R.A. Widenhoefer, X. Han, Eur. J. Org. Chem. (2006) 4555;
(l) T. Ishida, M. Haruta, Angew. Chem., Int. Ed. 46 (2007) 7154;
(m) D.J. Gorin, F.D. Toste, Nature 446 (2007) 395.
[3] (a) C.H.M. Amijs, V. López-Carrillo, A.M. Echavarren, Org. Lett. 9 (2007) 4021;
(b) M. Yu, G. Zhang, L. Zhang, Org. Lett. 9 (2007) 2147;
(c) S. Wang, L. Zhang, J. Am. Chem. Soc. 128 (2006) 8414.
[4] (a) G. Lemière, V. Gandon, K. Cariou, T. Fukuyama, A.-L. Dhimane, L.
Fensterbank, M. Malacria, Org. Lett. 9 (2007) 2207;
(b) A. Buzas, F. Gagosz, J. Am. Chem. Soc. 128 (2006) 12614;
(c) N. Marion, S. Díez-González, P. Frémont, A.R. Noble, S.P. Nolan, Angew.
Chem., Int. Ed. 45 (2006) 3647;
(d) L. Zhang, S. Wang, J. Am. Chem. Soc. 128 (2006) 1442.
[5] (a) A. Buzas, F. Istrate, F. Gagosz, Org. Lett. 8 (2006) 1957;
(b) L. Zhang, J. Am. Chem. Soc. 127 (2005) 16804;
R1 R2
(c) A.W. Sromek, A.V. Kel’in, V. Gevorgyan, Angew. Chem., Int. Ed. 43 (2004)
2280;
(d) T. Schwier, A.W. Sromek, D.M.L. Yap, D. Chernyak, V. Gevorgyan, J. Am.
Chem. Soc. 129 (2007) 9868.
R2
R2
R1
H
O
LAu OTf
O
O
R1
LAu
X
O
H
X
O
X
O
- H
1,3-OXO~
L = Ph3P
[6] For Au(I)-catalyzed synthesis of 2-acyloxy-1,3-dienes from allenes via formal
1,3-acyloxy migration, see: A. Buzas, F. Istrate, F. Gagosz, Org. Lett. 9 (2007)
985.
LAu
LAu
v
iv
1
[7] S. Wang, L. Zhang, Org. Lett. 8 (2006) 4585.
- LAu
+H
LAu
- LAu
O
[8] G. Li, G. Zhang, L. Zhang, J. Am. Chem. Soc. 130 (2008) 3740.
[9] A.S. Dudnik, T. Schwier, V. Gevorgyan, Org. Lett. 10 (2008) 1465.
[10] For general review, see: P.H. Ducrot, in: A.R. Katritzky, R.J.K. Taylor (Eds.),
Comprehensive Organic Functional Group Transformations II, vol. 1, Elsevier,
Oxford, UK, 2005, pp. 375–426.
R2
R1
R2
E
E
X = >CMe;
>P(OEt)2
•
OXO
X
O
H
R1
3
2
H
[11] (a) G. Saucy, R. Marbet, H. Lindlar, O. Isler, Helv. Chim. Acta 42 (1959) 1945;
(b) H. Schlossarczyk, W. Sieber, M. Hesse, H.-J. Hansen, H. Schmid, Helv. Chim.
Acta 56 (1973) 875;
Scheme 1. Mechanistic rationale for Au(I)-catalyzed cascade.
(c) R.C. Cookson, M.C. Cramp, P.J. Parsons, J. Chem. Soc., Chem. Commun.
(1980) 197.
[12] (a) There has been a recent discussion on the role of Brønsted acids in
homogenous transition metal-catalyzed reactions. For the most relevant
references, see: A.S.K. Hashmi, Catal. Today 122 (2007) 211;
(b) Z. Li, J. Zhang, C. Brouwer, C.-G. Yang, N.W. Reich, C. He, Org. Lett. 8 (2006)
4175;
X
X
O
O
O
O
H
H
H
H
(c) D.C. Rosenfeld, S. Shekhar, A. Takemiya, M. Utsunomiya, J.F. Hartwig, Org.
Lett. 8 (2006) 4179;
(d) J.U. Rhee, M.J. Krische, Org. Lett. 7 (2005) 2493.
vs
vs
RS
RL
RL
RS
Au
PPh3
B
A
Au
PPh3
[13] Representative procedure for the Au(I)-catalyzed isomerization of propargylic
esters 1 into (1E,3E)-dienes 2: To a foiled 25 ml flask with septa charged with
2.5 mol% of 1:1 mixture of Au(PPh3)Cl (6.2 mg, 0.0125 mmol) and AgOTf
(3.2 mg, 0.0125 mmol) and the 10 ml of anhydrous dichloromethane and
stirred for 15 min was then added propargylic phosphate 1a (141.15 mg,
0.5 mmol) under argon atmosphere and the reaction mixture was stirred at
room temperature for 1 h. The reaction mixture was then filtered through a
layer of flash Silica (EtOAc – eluent), the solvents were removed in vacuo, and
the residue was purified by column chromatography (EtOAc-Hex: 1:1) to give
diethyl (1E,3E)-4-phenylbuta-1,3-dien-1-yl phosphate 2a (117.4 mg, 83%): 1H
NMR (500 MHz, CDCl3) d 7.36 (s, 2H), 7.28–7.33 (m, 2H), 7.19–7.24 (m, 1H),
6.83 (dd, J = 11.92, 6.42 Hz, 1H), 6.64 (dd, J = 15.77, 11.00 Hz, 1H), 6.52 (d,
J = 15.77 Hz, 1H), 6.21 (t, J = 11.46 Hz, 1H), 4.15–4.24 (m, 4H), 1.37 (td, J = 7.11,
favored
RS
H
RS
H
OXO
RL
RL
OXO
H
H
H
H
C
D
Au
PPh3
Au
PPh3
Scheme 2. Stereoelectronic models A–D.

A.S. Dudnik et al. / Journal of Organometallic Chemistry 694 (2009) 482–485
485
1.01 Hz, 6H); 13C NMR (126 MHz, CDCl3) d 139.7 (d, JCP = 5.5 Hz), 137.1, 132.0,
[15] (a) For reviews, see: S.M. Allin, R.D. Baird, Curr. Org. Chem. 5 (2001) 395;
128.6, 127.5, 126.1, 122.9, 118.0 (d, JCP = 11.1 Hz), 64.6 (d, JCP = 5.5 Hz), 16.1 (d,
JCP = 5.5 Hz); HRMS (EI) calcd. for C14H19O4P: 282.10210. Found: 282.10225%.
[14] Unfortunately, employment of internal alkynes possessing alkyl- and aryl
substituents in this transformation led to unseparable mixtures of 1,3-dienes
in low yields.
(b) U. Nubbemeyer, Synthesis 7 (2003) 961;
(c) K.N. Fanning, A.G. Jamieson, A. Sutherland, Curr. Org. Chem. 10 (2006)
1007.