Diversity-oriented synthesis of functionalized 1-aminopyrroles by regioselective zinc chloride-catalyzed, one-pot 'conjugate addition/cyclization' reactions of 1,3-bis(silyl enol ethers) with 1,2-diaza-1,3-butadienes

Article abstract of DOI:10.1002/adsc.200800097

In a convenient one-pot process, the easily accessible 1,2-diaza-1,3- butadienes and 1,3-bis(silyl enol ethers) are converted into the previously unknown functionalized 1-aminopyrroles and 1-amino-4,5,6,7-tetrahydroindoles. The domino reaction proceeds through a zinc chloride-catalyzed Econjugate addition/cyclizationG sequence.

Full text of DOI:10.1002/adsc.200800097

FULL PAPERS
DOI: 10.1002/adsc.200800097
Diversity-Oriented Synthesis of Functionalized 1-Aminopyrroles
by Regioselective Zinc Chloride-Catalyzed, One-Pot ꢀConjugate
Addition/Cyclizationꢁ Reactions of 1,3-Bis(silyl enol ethers) with
1,2-Diaza-1,3-butadienes
Vahuni Karapetyan,a,b Satenik Mkrtchyan,a,b Andreas Schmidt,a
Orazio A. Attanasi,c,* Gianfranco Favi,c Fabio Mantellini,c Alexander Villinger,a
Christine Fischer,d and Peter Langera,d,*
a
Institut für Chemie, Universität Rostock, Albert Einstein Str. 3a, 18059 Rostock, Germany
Fax : (+49)-381-498-6410; e-mail: peter.langer@uni-rostock.de
Faculty of Chemistry, Yerevan State University, Alex Manoogian 1, 0025 Yerevan, Armenia
Istituto di Chimica Organica, Università degli Studi di Urbino “Carlo Bo”, Via I Maggetti 24, 61029 Urbino, Italy
Leibniz-Institut für Katalyse an der Universität Rostock e.V., Albert Einstein Str. 29a, 18059 Rostock, Germany
b
c
d
Received: February 14, 2008; Published online: May 16, 2008
Supporting information for this article is available on the WWW under http://asc.wiley-vch.de/home/.
Abstract: In a convenient one-pot process, the easily ceeds through a zinc chloride-catalyzed ꢀconjugate
accessible 1,2-diaza-1,3-butadienes and 1,3-bis(silyl addition/cyclizationꢁ sequence.
enolethers) are converted into the previousyl un-
known functionalized 1-aminopyrroles and 1-amino- Keywords: cyclizations; 1,2-diaza-1,3-butadienes; N-
4,5,6,7-tetrahydroindoles. The domino reaction pro- heterocycles; pyrroles; silyl enol ethers
Introduction
compounds is of considerable interest. The base-medi-
ated conjugate addition of nucleophiles to a,b-unsatu-
Pyrroles and pyrrolidines are present in many biologi- rated carbonylcompounds is of great synthetic utiil-
cally active natural products, such as the porphyrins, ty.[6] Mukaiyama and co-workers were the first to
phthalocyanines, various alkaloids, or vitamin B12. A report a Lewis acid-catalyzed variant of this reaction.
variety of synthetic compounds are of pharmacologi- These transformations, which proceed under mild
cal relevance and are used in the clinic. This includes, conditions, rely on the use of silyl enol ethers as the
for example, triprolidine, piracetam, anirolac, pyrvini- nucleophiles.[7,8]
um, fenpiclonil, pyrrolnitrin, stallimycin, tolmetin, zo-
Recently, some of us reported[9] the synthesis of 1-
mepirac, clemizole, dextromoramide, prostaglandin aminopyrroles and 1-aminoindoles by one-pot ꢀconju-
PGF2a, vinblastine, vincristine, vincamine, reserpine, gate addition/cyclizationꢁ reactions of simple silyl enol
and perfluoroalkylpyrroles.[1] Oligo- and polypyrroles ethers with 1,2-diaza-1,3-butadienes.[10,11] 1,3-Bis(silyl
also represent important electronic materials, due to enol ethers) represent electroneutral equivalents of
[12]
their high electroconductivity.[1,2] 1-Aminopyrroles 1,3-dicarbonyldianions.
Like dianions, they gener-
also represent pharmacologically important heterocy- ally react with electrophiles at their terminal carbon
cles. Recently, 1-aminopyrroles have been employed atom. One-pot cyclizations of 1,3-bis(silyl enol ethers)
as intermediates during the synthesis of analgesic[3] with oxalyl chloride,[13] 1,3-dielectrophiles,[14] pyryl-
and NMDA receptor antagonists.[4] Whereas a variety
ium[15] and iminium salts,[16] and other electrophiles[12]
ACHTREUNG
of pyrrole syntheses are known, methods for the have been reported. The Lewis acid-catalyzed con-
direct preparation of functionalized 1-aminopyrroles densation of 1,3-bis(silyl enol ethers) with 1,1-dime-
are rare.[5] Moreover, these approaches usually pres- thoxy-2-azidoethane and subsequent cyclization
ent significant limitations in terms of substitutent allows a convenient synthesis of functionalized pyr-
groups that can be introduced, the substitution pat- roles.[17] Recently, we have reported a catalytic one-
tern and/or the regioselectivity. Therefore, the devel- pot cyclization of 1,3-bis(silyl enol ethers) with 1,2-
opment of new methods for the synthesis of these diaza-1,3-butadienes which provides a convenient and
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Figure 1. Retrosynthetic approach of pyrroles and tetrahy-
droindoles.
direct approach to a variety of functionalized 1-ami-
nopyrroles.[18] Herein, we report full details of these
studies. With regard to our preliminary communica-
tion,[18] the scope has been considerably extended.
This synthetic strategy can be regarded as domino
ꢀconjugate addition/cyclizationꢁ reactions, allowing the
construction of 1-aminopyrrole rings in an efficient
manner from easily available intermediates (see
Figure 1).
It is noteworthy that these products are not readily
available by other methods. Moreover, the presence
of different groups in these systems confer an inter-
esting contribution to this work, making them suitable
as intermediates for more complex compounds.
Results and Discussion
The 1,3-bis(silyl enol ether) 2a was prepared from
[19]
Scheme 1. Possible mechanism of the formation of 1-amino-
pyrrole 3a; i: 1) ZnCl2 (0.2 equiv.), CH2Cl2, 208C, 12 h; 2)
TFA.
methylacetoacetate in two steps.
The ZnCl2-cata-
lyzed reaction of 2a with 1,2-diaza-1,3-butadiene 1a
and subsequent addition of trifluoroacetic acid (TFA)
afforded the 1-aminopyrrole 3a (Scheme 1). The best
yields were obtained when ZnCl2 and TFA were used methylsilyloxyethene) with 1,2-diaza-1,3-butadienes.
as the catalyst and for protonation, respectively. The In these studies, the progress of the reaction of 1a
reaction was carried out following the protocol as pre- with 1-methoxy-2-methyl-1-(trimethylsiloxy)-propene
viously reported for simple silyl enol ethers.[9]
was directly monitored by NMR. In addition, a silylat-
The generally accepted mechanism for the Lewis ed open-chain intermediate could be successfully iso-
acid-catalyzed conjugate addition of silyl enol ethers lated and structurally characterized when the reaction
to Michaelacceptors invovles an activation of the
was stopped immediately after the disappearance of
[9]
latter by the Lewis acid.[20] Some of us earlier report- the starting material(TLC contro)l.
In fact, our pre-
ed[9] mechanistic studies related to the reaction of vious studies suggested that the silyl enol ether rather
simple silyl enol ethers (such as 1-methoxy-1-tri- than the diazadiene is activated by the Lewis acid.
ACHTREUNGmethylsilyloxyethene or 2,2-dimethyl-1-methoxy-1-tri- Accordingly, we assume that the regioselective forma-
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Diversity-Oriented Synthesis of Functionalized 1-Aminopyrroles
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Scheme 3. Synthesis of 3ar and 3as; i: 1) ZnCl2 (0.2 equiv.),
CH2Cl2, 208C, 12 h; 2) TFA.
Scheme 2. Synthesis of 1-aminopyrroles 3a–3aq; i: 1) ZnCl2
(0.2 equiv.), CH2Cl2, 208C, 12 h; 2) TFA.
tion of 3a can be explained by ZnCl2-catalyzed attack
of the terminalcarbon atom of 2a at the terminal
carbon of the azo-ene system of 1a (Mukaiyama–Mi-
chaeladdition) to give intermediate B. In analogy to
our previous studies,[9] the short-lived silylhydrazonic
intermediate A is also hypothesized. The addition of
TFA subsequently results in the cleavage of the silyl
groups to give intermediate C. The latter undergoes
an acid-catalyzed cyclization (by attack of the nitro-
gen atom to the carbonylgroup) to give intermediate
D. Subsequently, the acid-catalyzed elimination of a
water molecule affords the final product 3a
(Scheme 1).
The addition/cyclization of various 1,3-bis(silyl enol
ethers) 2a–ab with 1,2-diaza-1,3-butadienes 1a–e af-
forded the novel1-aminopyrroels
3a–aq (Scheme 2,
Figure 2. Ortep plot of 3ai.
Table 1). 1-Aminopyrroles were successfully prepared
from 1,3-bis(silyl enol ethers) derived from b-keto
esters (products 3a–d, 3i–k, 3m–ak) or 1,3-diketones
(3e–h, 3l), from open-chained (3a–w, 3aj, 3ak, 3ao,
3ap) or cyclic 1,3-dicarbonyl compounds (3x–3ai), and Conclusions
from non-substituted (3a–g, 3j–n, 3s) or substituted
1,3-dicarbonylcompounds ( 3h, i, 3o–r, 3t–w, 3aj, 3ak, In conclusion, we have reported the regioselective
3ao, 3ap). The cyclizations generally proceeded in synthesis of functionalized 1-aminopyrroles by ZnCl2-
moderate to excellent yield (except for 3aj, 3ak). The catalyzed one-pot ꢀconjugate addition/cyclizationꢁ re-
employment of the 7-membered cyclic bis(silyl enol actions of 1,3-bis(silyl enol ethers) with 1,2-diaza-1,3-
ether) 2x, of 1,1,1-trifluoro-2,4-bis(trimethylsilyloxy)- butadienes. These reactions are easy to carry out, pro-
pentane-2,4-diene 2y, and of methoxy-substituted ceed under mild conditions and with high yields. It is
diene 2z proved to be unsuccessful. The failure of 2y noteworthy that the products are not directly avail-
can be explained by its low reactivity. The failure of able from the b-dicarbonylcompounds. In fact, previ-
2z might be explained by compe-ting chelation of the ous investigations[5b,10a] have shown that the reactions
Lewis acid by the additionalmethoxy group. Note-
between 1,2-diaza-1,3-butadiene and b-keto esters or
worthy, the employment of the amide 1e failed.
1,3-diketones proceed by base-catalyzed nucleophilic
The cyclization of 1,2-diaza-1,3-butadienes 1a and attack of the activated methylene group at the hetero-
1d with 1,3-bis(silyl enol ether) 2ac, prepared from cy- diene system leading to regioisomeric 1-aminopyr-
clohexane-1,3-dione, afforded the 1-amino-4,5,6,7-tet- roles. The 1-aminopyrroles prepared represent useful
rahydroindol-6-ones 3ar and 3as, respectively synthetic building blocks. For example, it has been re-
(Scheme 3).
ported previously that 1-aminopyrroles, including de-
The structures of all products were established by rivatives containing a urea moiety (similar to products
spectroscopic methods. The structure of 3ai was inde- 3a–as), can be transformed into the corresponding
pendently confirmed by X-ray crystal structure analy- pyrroles by reaction with Cr CHTREUNG
(OAc)4,[22] KO-t-Bu/
2A
sis (Figure 2).[21]
DMF,[23] or H2/Raney Ni,[24] or by diazotation.[25]
Adv. Synth. Catal. 2008, 350, 1331 – 1336
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Vahuni Karapetyan et al.
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Table 1. Synthesis of 1-aminopyrroles 3a–aq.
1
2
3
R1
R2
R3
R4
R5
Yield [%] of 3[a]
a
a
a
a
a
a
a
a
a
b
c
b
c
d
d
c
a
a
a
d
a
d
a
a
d
a
d
a
d
a
d
a
d
a
d
a
d
a
a
a
a
a
e
a
b
c
d
e
f
g
h
i
b
b
e
j
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
p
q
r
s
t
u
v
w
x
y
z
aa
ab
ac
ad
ae
af
ag
ah
ai
aj
ak
al
am
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
Me
Me
Me
Me
Me
Me
Me
Me
Me
Et
H
H
H
H
H
H
H
Me
Et
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
OMe
OEt
O-i-Bu
O-t-Bu
Me
t-Bu
Ph
Et
OMe
OEt
OEt
Me
64
92
80
81
56
82
60
86
71
60
61
72
60
52
65
63
44
47
60
75
74
97
63
50
53
40
35
97
87
79
61
49
37
42
46
20
20
0
OEt
OMe
O-t-Bu
OMe
O-t-Bu
OMe
OMe
O-t-Bu
OEt
OEt
OEt
OMe
OEt
OMe
OEt
OEt
OMe
OEt
OMe
OEt
OMe
OEt
OMe
OEt
OMe
OEt
OMe
OEt
OMe
OEt
Me
Et
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
O
O
ACHTREUNG
ACHTREUNG
j
H
k
k
l
n-Hex
n-Hex
Allyl
n-Oct
H
n-Hept
n-Hept
n-Pr
n-Pr
H
OMe
OMe
OMe
OEt
OBn
OEt
m
n
o
o
p
p
q
q
r
r
s
s
t
OEt
OMe
OMe
-(CH2)2O-
-(CH2)2O-
OMe
OMe
OEt
H
-(CH2)2-
-(CH2)2-
-(CH2)3-
-(CH2)3-
OEt
-CH2CHMeCH2-
-CH2CHMeCH2-
-CHMeCH2CH2-
-CHMeCH2CH2-
-(CH2)9-
OMe
OMe
OEt
OEt
OMe
OMe
t
u
u
v
v
w
w
x
y
z
-(CH2)9-
CH2CH2ClH
CH2CH2ClH
-(CH2)4-
H
OMe
H
OEt
OEt
OMe
CF3
OMe
OEt
OMe
OMe
OEt
OEt
OEt
OEt
H
H
Me
Et
H
0
0
45
40
0
an
aa
ab
a
ao
ap
aq
H
H
NMe2
[a]
Isolated yields.
General Procedure for the Synthesis of 1-Aminopyr-
roles 3 by Mukaiyama–Michael-Type Reactions of
1,3-Bis(silyl enol ethers) with 1,2-Diaza-1,3-
butadienes
Experimental Section
General Comments
The spectroscopic data of all compounds are given in the
supporting information.
To a CH2Cl2 solution (12 mL) of 1,2-diaza-1,3-butadiene 1
(2.0 mmol) were added 1,3-bis(silyl enol ether) 2 (2.4 mmol)
and freshly dried ZnCl2 (0.055 g, 0.4 mmol) at 208C. The so-
lution was stirred for 12 h at room temperature and subse-
quently TFA (0.3 mL) was added. The solvent was removed
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Diversity-Oriented Synthesis of Functionalized 1-Aminopyrroles
FULL PAPERS
under vacuum and the residue was purified by column chro-
matography (silica gel, heptane!heptane/EtOAc=1:2).
kaiyama, Chem. Lett. 1994, 97–100; j) B. C. Ranu, M.
Saha, S. Bhar, J. Chem. Soc. Perkin Trans. 1 1994,
2197–2199; k) J. Otera, T. Sato, H. Nozaki, in: Stereo-
controlled Organic Synthesis, (Ed.: B. M. Trost),
IUPAC, Oxford, 1994, pp 117–144; l) L. A. Telan, C.-
D. Poon, S. A. Evans, Jr., J. Org. Chem. 1996, 61, 7455–
7462; m) S. Sankararaman, R. Sudha, J. Org. Chem.
1999, 64, 2155–2157; n) K. Takasu, S.-J. Ueno, K. Ina-
naga, M. Ihara, J. Org. Chem. 2004, 69, 517–521; o) Z.-
L. Shen, S. J. Ji, T.-P. Loh, Tetrahedron Lett. 2005, 46,
507–508.
Acknowledgements
We thank Mr. Gnuni Karapetyan for helpful discussions. Fi-
nancial support from the State of Mecklenburg-Vorpommern
(scholarships for A. S. and V. K.), fromthe DAAD (scholar-
ship for S. M.) and fromthe Ministero dell ’Università, dell’Is-
truzione e della Ricerca (MIUR) - Rome, Università degli
Studi di Urbino “Carlo Bo” is gratefully acknowledged.
[9] O. A. Attanasi, G. Favi, P. Filippone, S. Lillini, F. Man-
tellini, D. Spinelli, M. Stenta, Adv. Synth. Catal. 2007,
349, 907–915.
[10] a) O. A. Attanasi, L. De Crescentini, P. Filippone, F.
Mantellini, S. Santeusanio, Arkivoc 2002, xi, 274–292;
b) O. A. Attanasi, L. De Crescentini, G. Favi, P. Fili-
ppone, F. Mantellini, S. Santeusanio, J. Org. Chem.
2004, 69, 2686–2692; c) O. A. Attanasi, G. Favi, P. Fili-
References
[1] a) R. J. Sundberg, in: Comprehensive Heterocyclic
Chemistry, (Eds.: A. R. Katritzky, C. W. Rees), Perga-
mon Press, Oxford, 1984, Vol. 4, p 314; b) G. W. Grib-
ble, in: Comprehensive Heterocyclic Chemistry II,
(Eds.: A. R. Katritzky, C. W. Rees, E. F. V. Scriven),
Pergamon-Elsevier Science, Amsterdam, 1996, Vol. 2,
Chapter 4.
[2] M. I. Goller, C. Barthet, G. P. McCarthy, R. Corradi,
B. P. Newby, S. A. Wilson, S. P. Armes, S. Y. Luk, Coll.
Polym. Sci. 1998, 276, 1010–1018.
ˇ
ppone, A. Golobic, B. Stanovnik, J. Svete, J. Org.
Chem. 2005, 70, 4307–4313; d) O. A. Attanasi, G. Bac-
colini, C. Boga, L. De Crescentini, P. Filippone, F. Man-
tellini, J. Org. Chem. 2005, 70, 4033–4037; e) O. A. At-
tanasi, L. De Crescentini, G. Favi, P. Filippone, S. Lilli-
ni, F. Mantellini, S. Santeusanio, Org. Lett. 2005, 7,
2469–2471; f) O. A. Attanasi, G. Favi, P. Filippone, G.
Giorgi, S. Lillini, F. Mantellini, F. R. Perrulli, Synlett
2006, 2731–2734; g) O. A. Attanasi, L. De Crescentini,
[3] R. C. Effland, J. T. Klein, US Patent 4,546,105, 1985;
Chem. Abstr. 1986, 104, 186307.
ˇ
G. Favi, P. Filippone, A. Golobic, S. Lillini, F. Mantelli-
[4] J. Kulagowski, J. Janusz, P. D. Leeson, UK Patent
2,265,372, 1993; Chem. Abstr. 1993, 120, 134504.
[5] For select examples: a) G. S. Gadaginamath, A. S.
ni, Synlett 2006, 2735–2738; h) O. A. Attanasi, P.
Davoli, G. Favi, P. Filippone, A. Forni, G. Moscatelli, F.
Prati, Org. Lett. 2007, 9, 3461–3464; i) O. A. Attanasi,
G. Giorgi, G. Favi, P. Filippone, S. Lillini, F. R. Perrulli,
S. Santeusanio, Synlett 2007, 1691–1694; j) O. A. Atta-
nasi, G. Giorgi, G. Favi, P. Filippone, S. Lillini, F. R.
Perrulli, S. Santeusanio, Synlett 2007, 1691–1694.
[11] a) K. N. Zelenin, V. A. Nikitin, N. M. Anodina, Khim.
Geterotsikl. Soedin. 1973, 124–128; b) S. Sommer,
Chem. Lett. 1977, 583–586; c) S. Sommer, Angew.
Chem. Int. Ed. Engl. 1977, 16, 59–60; d) T. L. Gilchrist,
R. Sanchez, R. C. Wasson, J. Chem. Soc. Perkin Trans.
1 1989, 353–359; e) K. Banert, in: Targets in Heterocy-
clic Systems – Chemistry and Properties, (Eds.: O. A.
Attanasi, D. Spinelli), Società Chimica Italiana, Rome,
1999, Vol. 3, pp 1–32; f) S. Polanc, in: Targets in Heter-
ocyclic Systems – Chemistry and Properties, (Eds.:
O. A. Attanasi, D. Spinelli), Società Chimica Italiana,
Rome, 1999, Vol. 3, pp 33–92; g) R. K. Boeckman, Jr.,
P. Ge, J. E. Reed, Org. Lett. 2001, 3, 3647–3650;
h) R. K. Boeckman, Jr., P. Ge, J. E. Reed, Org. Lett.
2001, 3, 3651–3653; i) M. Kim, H.-J. Gais, J. Org.
Chem. 2006, 71, 4642–4650; j) D. Aparicio, O. A. Atta-
nasi, P. Filippone, R. Ignacio, S. Lillini, F. Mantellini, F.
Palacios, J. M. de Los Santos, J. Org. Chem. 2006, 71,
5897–5905.
Shyadligeri Indian J. Chem.
B 2000, 39, 31–35;
b) O. A. Attanasi, L. De Crescentini, G. Favi, P. Fili-
ppone, F. Mantellini, S. Santeusanio, J. Org. Chem.
2002, 67, 8178–8181; c) Y. Zhang, J. W. Herndon, Org.
Lett. 2003, 5, 2043–2045.
[6] P. Perlmutter, Conjugate Addition Reactions in Organic
Synthesis, Pergamon Press, Oxford, 1992.
[7] a) K. Narasaka, K. Soai, T. Mukaiyama, Chem. Lett.
1974, 1223–1224; b) K. Narasaka, K. Soai, Y. Aikawa,
T. Mukaiyama, Bull. Chem. Soc. Jpn. 1976, 49, 779–
783; c) K. Saigo, M. Osaki, T. Mukaiyama, Chem. Lett.
1976, 163–164; d) T. Mukaiyama, Angew. Chem. 1977,
89, 858–866; Angew. Chem. Int. Ed. Engl. 1977, 16,
817–826; e) T. Mukaiyama, Challenges in Synthetic Or-
ganic Chemistry, (translated by E. Baldwin), Clarendon
Press, Oxford, 1990.
[8] a) T. Mukaiyama, S. Matsui, K. Homma, S. Kobayashi,
Bull. Chem. Soc. Jpn. 1990, 63, 2687–2690; b) T. Sato,
Y. Wakahara, J. Otera, H. Nozaki, Tetrahedron 1991,
47, 9773–9782, and references cited therein; c) S. Ko-
bayashi, I. Hachiya, T. Takahori, Tetrahedron Lett.
1992, 33, 6815–6818; d) S. Mizukami, N. Kihara, T.
Endo, Tetrahedron Lett. 1993, 34, 7437–7440; e) B. C.
Ranu, M. Saha, S. Bhar, Tetrahedron Lett. 1993, 34,
1989–1990; f) C. LeRoux, H. Gaspard-Iloughmane, J.
Dubac, J. Jaud, P. Vignaux, J. Org. Chem. 1993, 58,
1835–1839; g) C. L. Roux, H. Gaspard-Iloughmane, J.
Dubac, Bull. Soc. Chim. Fr. 1993, 130, 832–842; h) G.
Dujardin, J. M. Poirier, Bull. Soc. Chim. Fr. 1994, 131,
900–909; i) S. Kobayashi, S. Suda, M. Yamada, T. Mu-
[12] Review: P. Langer, Synthesis 2002, 441–459.
[13] Review: P. Langer, Synlett 2006, 3369–3381.
[14] Review: H. Feist, P. Langer, Synthesis 2007, 327–347.
[15] Review: P. Langer, Synlett 2007, 1016–1025.
[16] Review: P. Langer, Eur. J. Org. Chem. 2007, 2233–
2238.
Adv. Synth. Catal. 2008, 350, 1331 – 1336
ꢂ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
1335

Vahuni Karapetyan et al.
FULL PAPERS
[17] E. Bellur, H. Gçrls, P. Langer, J. Org. Chem. 2005, 70,
4751–4761.
[18] A. Schmidt, V. Karapetyan, O. A. Attanasi, G. Favi, H.
Gçrls, F. Mantellini, P. Langer, Synlett 2007, 2965–
2968.
[19] G. A. Molander, K. O. Cameron, J. Am. Chem. Soc.
1993, 115, 830–846.
[20] a) S. J. Blarer, W. B. Schweizer, D. Seebach, Helv.
Chim. Acta 1982, 65, 1637–1654; b) M. Miyashita, T.
Yanami, T. Kumazawa, A. Yoshikoshi, J. Am. Chem.
Soc. 1984, 106, 2149–2156; c) D. Seebach, M. A.
Brook, Helv. Chim. Acta 1985, 68, 319–324; d) T. Mu-
kaiyama, M. Tamura, S. Kobayashi, Chem. Lett. 1986,
1017–1020; e) M. A. Brook, D. Seebach, Can. J. Chem.
1987, 65, 836–850; f) for an example of electron trans-
fer mechanism involving silyl ketene acetal and Lewis
acid-coordinated Michaelacceptor, see: T. Sato, Y. Wa-
kahara, J. Otera, H. Nozaki, S. Fukuzumi, J. Am.
Chem. Soc. 1991, 113, 4028–4030.
[21] CCDC 677345 contains the supplementary crystallo-
graphic 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
or can be ordered from the following address: Cam-
bridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: (+44)-1223–1336–033
or deposit@ccdc.cam. ac.uk).
[22] a) G. R. Martinez, P. A. Grieco, C. V. Srinivasan, J.
Org. Chem. 1981, 46, 3760–3761; b) G. R. Martinez,
P. A. Grieco, E. Williams, K.-i. Kanai, C. V. Srinivasan,
J. Am. Chem. Soc. 1982, 104, 1436–1438.
[23] G. Macaluso, G. Cusmano, G. Cirrincione, A. M. Al-
merico, P. Diana, Heterocycles 1991, 32, 1973–1981.
[24] a) G. Chelucci, M. Marchetti, J. Heterocycl. Chem.
1988, 25, 1135–1137; b) M. Satomura, J. Org. Chem.
1993, 58, 3757–3760.
[25] A. J. G. Baxter, J. Fuher, S. J. Teauge, Synthesis 1994,
207–211.
1336
asc.wiley-vch.de
ꢂ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2008, 350, 1331 – 1336