Decarboxylative Knoevenagel-type reactions on tetronamides: Synthesis of 5-ylidene-4-amino-2(5 H)-furanones

Article abstract of DOI:10.1055/s-0034-1378276

A detailed account regarding the synthesis of 5-ylidene-2(5H)-furanones is given. The key step is a decarboxylative Knoevenagel-type reaction of tetronamides with various α-functionalized aldehydes. The synthesis of protected basidalin is presented. Georg

Full text of DOI:10.1055/s-0034-1378276

LETTER
▌1713
lDetteercarboxylative Knoevenagel-Type Reactions on Tetronamides: Synthesis of
-Ylidene-4-Amino-2(5H)-Furanones
5
Alexandre Ear, Valérie Toum,a,b Serge Thorimbert,a,b Luc Dechoux*a,b
a
)-F,buranones
a
Sorbonne Universités. UPMC Univ Paris 06, UMR CNRS 8232, Institut Parisien de Chimie Moléculaire, 75005 Paris, France
E-mail: luc.dechoux@upmc.fr
b
CNRS UMR 8232, Institut Parisien de Chimie Moléculaire, 75005 Paris, France
Received: 11.04.2014; Accepted after revision: 11.05.2014
cus naucina. This natural product exhibits antibacterial
Abstract: A detailed account regarding the synthesis of 5-ylidene-
and antitumor activities, and its structure was elucidated
in 1983 by X-ray diffraction analysis. To the best of our
2
(5H)-furanones is given. The key step is a decarboxylative
Knoevenagel-type reaction of tetronamides with various α-func-
tionalized aldehydes. The synthesis of protected basidalin is pre- knowledge only the synthesis of the non-natural E isomer
9
1
0
sented.
has been described. Thiobasidalin, the thiolactone ana-
logue of basidalin, has been synthesized by Stachel and
Key words: Knoevenagel–Doebner reaction, β-enaminoesters, tet-
ronamides, 4-amino-2(5H)-furanones, basidalin
1
1
co-workers. Therefore, it was of interest to evaluate the
preparation of basidalin by means of a process that would
make use of glyoxal derivatives and the pivotal tetron-
amide 2 as reaction partners in a Knoevenagel–Doebner-
Amino-2(5H)-furanones, commonly referred to as tetron-
amides, are important intermediates in the synthesis of
natural products, and they are also of interest in the phar-
maceutical and agrochemical arenas. Most methods re-
ported for the preparation of substituted tetronamides are
based on the nucleophilicity of the enamine function. A
sequence involving condensation of primary or secondary
amines with tetronic acid followed by alkylation or aldol-
ization using, most generally, tert-butyllithium as a base
furnishes 5-substituted tetronamides. We have described
a novel N-bromosuccinimide (NBS) -promoted cycliza-
tion of enaminoesters 1 to 4-amino-5-carboxymethyl-
2
12
type reaction (Scheme 2).
1
2
CHO
CHO
MeO2C
RHN
O
HO
O
O
3
O
O
O
MeO2C
H2N
RHN
Scheme 2
4
5
Though the Knoevenagel–Doebner reaction has been ex-
tensively used in organic synthesis, only few examples
have been documented with α-functionalized aldehydes
6
(5H)-furanones 2 and subsequent C5-alkylation to pre-
1
3
such as dialkyl acetals of aldehydes in aldose chemistry.
Most generally, the reaction involves aromatic aldehydes,
pare 5-substituted tetronamides 3 in an overall three-step
approach (Scheme 1).7
1
4
giving access to cinnamic acid derivatives. The classical
Knoevenagel–Doebner reaction is carried out in a solvent
such as pyridine, catalyzed by secondary amines, com-
MeO2C
BnHN
MeO2C
H
R
O
NBS
O
15
O
monly piperidine. The List group has demonstrated that
aliphatic aldehydes react effectively using DMAP as cat-
O
BnHN
BnHN
CO2Me
3
16
H
alyst, while Zhenyuan and Wannian demonstrated that
1
2
β-alanine and DBU catalyzes the reaction with aromatic
1
7
Scheme 1
aldehydes. Recently, the group of Sandhu published a
solvent-free Doebner–Knoevenagel reaction between aro-
matic and heteroaromatic aldehydes and malonic acid
In our continuing efforts to develop efficient C5 modifica-
tions of tetronamides, we were interested in the possibility
of preparing 5-ylidene-4-amino-2(5H)-furanones 6.
Though the synthesis of these heterocyclic derivatives
have been described (most often obtained as unexpected
products through thermal rearrangements of azido- or
1
8
with alum [KAl(SO ) ·12H O] as catalyst. Kallikat
4 2
2
Augustine’s group used gem-dibromomethylarenes as an-
alogues of aldehydes with malonic acid in the synthesis of
1
9
cinnamic acid derivatives. Some examples of micro-
wave-assisted Knoevenagel–Doebner reactions of aro-
2
0
8
matic aldehydes have also been described. Bifunctional
polymeric catalysts have been successfully used in the ste-
isoxazoloquinones), no direct methylene insertion onto
the C5 position of tetronamides has been reported. More-
over, this structural framework is found in basidalin, a
natural product isolated from the mushroom Leucoagari-
2
1
reoselective synthesis of (E)-cinnamates, and a synthe-
sis of β-keto esters starting from β-ketoacids has been
2
2
described by Taddei.
We report herein the decarboxylative Knoevenagel-type
reaction of conjugated diester precursors, such as buteno-
lide ester 2, and an approach to the synthesis of basiladin.
SYNLETT 2014, 25, 1713–1716
Advanced online publication: 06.06.2014
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DOI: 10.1055/s-0034-1378276; Art ID: st-2014-d0306-l
Georg Thieme Verlag Stuttgart · New York
©

1714
A. Ear et al.
LETTER
The choice of the aldehyde was crucial since it has to de- Table 1 Synthesis of Compounds 6
liver the conjugate formyl function of basidalin in a few
R1
1
2
) NaOH (2 equiv)
) 1 M HCl
steps. We thus first considered the use of glyoxal in the
presence of NaOH, K CO , or LiHMDS to promote the
MeO C
2
O
O
O
1
2
3
O
+ R CHO
deprotonation of tetronamide 2, but only decomposition
of the starting material was observed.
2
2
R HN
R HN
H
6
2
or 2'
We thus turned our attention to the use of dimethoxyacet-
aldehyde and ethyl glyoxylate. By treating tetronamide 2 Entry R1
R2
Product Z/E of 6 Yield (%)
with one equivalent of NaOH in wet THF, we isolated the
1
2
3
4
5
6
CH OH
Bn
PMB
H
6d
6e
6f
92:8
>95:5
>95:5
>95:5
90:10
>95:5
–
67
79
35a
79
49
54
0
expected aldol products 4b,c in good yields. A further
treatment of compounds 4b and 4c with one equivalent of
NaOH followed by an acidic quench led quantitatively to
the formation of products 5b and 5c, respectively (path a,
Scheme 3). More interestingly, the same reactions per-
formed in the presence of two equivalents of NaOH fol-
lowed by an acidic quench led directly to the
decarboxylated products 5b and 5c as mixtures of two
diastereoisomers in 50:50 and 70:30 ratios, respectively
2
CH OH
2
CH OH
2
Ph
Bn
Bn
Bn
Bn
6g
6h
6i
Me
Me(CH2)10
7
Et CO
6j
(path b, Scheme 3).
2
a
1
Evaluated by H NMR analysis of the crude product mixture.
NaOH (1 equiv)
R
O
MeO2C
O
HO
O
+
THF–H O
2
R
MeO2C
OHC
O
2
observed starting from unprotected tetronamide 2 (R = H,
r.t.
BnHN
path a
Table 1, entry 3).
BnHN
2
Aromatic or aliphatic aldehydes such as benzaldehyde
(Table 1, entry 4), acetaldehyde (Table 1, entry 5), and do-
decanal (Table 1, entry 6) were also productive in this
novel decarboxylative Knoevenagel reaction. In all cases
the Z diastereoisomers 6d–i were formed with excellent
stereoselectivities. The assignment of the Z or E configu-
4
4
4
a R = CHO, degradation
b R = CH(OMe)2, 89%
c R = CH2CO2Et, 86%
1
2
) NaOH–THF–H2O
) 1 M HCl
R
1
2
) NaOH (2 equiv), THF–H2O HO
) 1 M HCl
1
O
O
ration of the double bond was achieved by H NMR anal-
H
ysis of the chemical shifts of the NH proton of both
stereoisomers of compound 6d (vide infra), as the NH
proton is deshielded in the E isomer appearing around 10
ppm; whereas the proton of the Z isomer presents standard
path b
BnHN
5
5
b R = CH(OMe)2, 98%
c R = CH2CO2Et, 86%
2
4
chemical shift around 6 ppm.
Scheme 3 Knoevenagel-type reactions
The reaction of 2 with a ketone such as pentan-3-one gave
neither the Knoevenagel–Doebner nor the aldol products
but the decarboxylated tetronamide 8 in quantitative
To our surprise, all standard acidic conditions examined
to deprotect the acetal function or to eliminate the hydrox-
yl group of 5b,c were unsuccessful. Both acetal and alco-
hol functions were stable in the presence of trifluoroacetic
acid, 6 M HCl, or aqueous toluenesulfonic acid. Further-
more, compounds 5b and 5c could not be dehydrated us-
ing trifluoroacetic anhydride in presence of base, as has
2
5
yield.
Concerning the mechanism of this novel one-pot decar-
boxylative Knoevenagel-type reaction, it is interesting to
note that the first step should be a classical condensation
leading to aldol adduct 4. The second step is the saponifi-
cation of the ester group; whereas the slower dehydration–
decarboxylation is only promoted by the acidic medium
(aq HCl) during the third step. As the formation of aldols
2
3
been reported in the synthesis of pulvinic acids. Instead,
we observed selective trifluoroacetylation on C3 as previ-
ously described.3a
5
d–i was not observed, we speculate that the decarboxyl-
To our satisfaction, the reaction of 2 with other aldehydes
led to more useful products (Table 1). Indeed, when the
reaction was conducted with dimeric glycolaldehyde, we
observed the formation of the expected decarboxylated
Knoevenagel-type product 6d in 67% yield (Table 1, en-
try 1). Starting with the para-methoxybenzyl-protected
2
6
ation is concomitant with dehydration. We propose an
asynchronous concerted mechanism in which a positive
charge is developed, induced by the departure of the alco-
hol function. This E -like mechanism can explain why the
1
reactions with dimethoxyacetaldehyde and ethyl glyoxyl-
ate (Scheme 3), in which the development of such positive
charge α to an electron-withdrawing group is strongly dis-
favored, yield adducts 4 and why there is a discrepancy
2
compound 2′ (R = PMB) significantly increased the yield
of product 6e to 79% (Table 1, entry 2). In contrast, a low-
er yield, associated with difficulties to purification, was
Synlett 2014, 25, 1713–1716
© Georg Thieme Verlag Stuttgart · New York

LETTER
Synthesis of 5-Ylidene-4-Amino-2(5H)-Furanones
1715
between the diastereoselectivities observed for the forma-
tion of aldols 4 and alkenes 6.
H
2
O (2 × 2 mL), dried over anhydrous MgSO , filtered, and evapo-
4
rated. The residue was purified by silica gel column chromatogra-
phy to afford the (Z)-3-(benzylamino)-[5-oxo-(5H)-furan-2-
ylidene]acetaldehyde (7d) {or (Z)-3-(p-methoxybenzylamino)-[5-
oxo-(5H)-furan-2-ylidene]acetaldehyde (7e)}.
HO
CHO
SO3⋅py
Et3N, DMSO
O
O
O
Compound 7d
O
–1 1
IR (NaCl): ν = 3317, 1753, 1739, 1636, 1615 cm . H NMR (250
CH2Cl2
MHz, CDCl ): δ = 4.41 (d, J = 5.5 Hz, 2 H), 4.98 (s, 1 H), 5.68 (d,
3
PHN
PHN
d–e
J = 7.5 Hz, 1 H), 5.84–5.87 (s, NH), 7.29–7.42 (m, 5 H, Ph), 10.10
7
7
d P = Bn, 76%
e P = PMB, 79%
6
13
(
d, J = 7.5 Hz, 1 H). C NMR (62.5 MHz, CDCl ): δ = 49.7, 84.5,
3
1
02.2, 127.8, 128.7, 129.4, 135.3, 157.5, 158.3, 167.7, 189.3.
+
Scheme 4 Synthesis of protected (Z)-basidalin
HRMS: m/z [M + Na] calcd for C H NO : 252.0631; found:
13 11 3
2
52.0633.
Compound 7e
Pyridinium chlorochromate oxidation of the allylic alco-
hol 6f did not lead to the expected basidalin. This could be
due to overoxidation of the unprotected nitrogen atom in
compound 6f. On the other hand, oxidation of 6d and 6e
1
H NMR (250 MHz, CDCl ): δ = 3.82 (s, 3 H), 4.33 (d, J = 5.5 Hz,
3
2
H), 5.00 (s, 1 H), 5.30 (s, NH), 5.58 (d, J = 7.5 Hz, 1 H), 6.91 (d,
J = 8.0 Hz, 2 H), 7.21 (d, J = 8.0 Hz, 2 H), 10.13 (d, J = 7.5 Hz, 1
13
H). C NMR (62.5 MHz, CDCl ): δ = 49.0, 55.4, 84.3, 102.2,
3
2
7
with SO ·pyridine gave the corresponding aldehydes 7d 114.5, 127.0, 129.0, 129.2, 159.9, 157.1, 158.1, 167.5, 189.0.
3
+
and 7e in good yields (Scheme 4). Attempts to remove the HRMS: m/z [M + Na] calcd for C14
H13NO : 282.0736; found:
4
2
82.0736.
p-methoxybenzyl group were conducted on aldehyde 7e
using ceric ammonium nitrate,28 DDQ, and TFA.
29
30
However, although the formation of p-methoxybenzalde-
hyde was observed, basidalin could not be isolated from
the mixture.
Acknowledgment
We wish to thank CNRS, UPMC for funding. FR2769 is acknow-
ledged for technical assistance. V.T. thanks the ‘Ministère de l’Edu-
In conclusion, we have described a methodology wherein cation Nationale, de l’Enseignement Supérieur et de la Recherche’
for a fellowship.
C5 ester-substituted tetronamide 2 can be employed as
malonate equivalent in the Knoevenagel–Doebner reac-
tion for the synthesis of 5-ylidene-4-amino-2(5H)-fura-
nones. The process is mild, efficient, and practical. Some
insights into the mechanism of the reaction and an appli-
cation to the synthesis of two protected basidalin deriva-
tives are presented.
References and Notes
(1) (a) Schlessinger, R. H.; Yu, Y. J. J. Am. Chem. Soc. 1996,
1
18, 3301. (b) Clark, J. S.; Marlin, F.; Nay, B.; Wilson, C.
Org. Lett. 2003, 5, 89. (c) Samaritani, S.; Bruyère, H.;
Ballereau, S.; Royer, J. C. R. Chimie 2005, 8, 841.
(
d) Bruyère, H.; Dos Reis, C.; Samaritani, S.; Ballereau, S.;
Royer, J. Synthesis 2006, 1673.
General Procedure for the Preparation of Compounds 6
(2) For some examples, see: Wang, J.; Jiang, X.; Chen, M.; Ge,
Z.; Hu, Y.; Hu, H. J. Chem. Soc., Perkin Trans. 1 2001, 66.
(3) (a) Zhou, L.-H.; Yu, X.-Q.; Pu, L. J. Org. Chem. 2009, 74,
2013. (b) Hertzberg, R.; Moberg, C. J. Org. Chem. 2013, 78,
9174; and references cited therein.
(4) (a) Nishide, K.; Aramata, A.; Kamanaka, T.; Inoue, T.;
Node, M. Tetrahedron 1994, 50, 8337. (b) Dankwardt, S.
M.; Dankwardt, J. W.; Schlessinger, R. H. Tetrahedron Lett.
To a solution of tetronamide 2 (0.88 mmol) in THF (10 mL) was
added NaOH (0.07 g; 1.76 mmol) in H O (1 mL), followed by the
2
aldehyde (0.88 mmol), and the mixture was stirred for 30 min.
Then, 10% HCl was added, and the solution was stirred overnight.
The mixture was then extracted with CH Cl , dried over anhydrous
2
2
MgSO , filtered, and evaporated. The residue was purified by silica
4
gel column chromatography to afford compounds 6d–i.
1
998, 39, 4971. (c) Dankwardt, S. M.; Dankwardt, J. W.;
Schlessinger, R. H. Tetrahedron Lett. 1998, 39, 4975.
d) Dankwardt, S. M.; Dankwardt, J. W.; Schlessinger, R. H.
Compound 6d
-1 1
IR (NaCl): ν = 3616, 3321, 1739, 1614 cm . H NMR (250 MHz,
MeOD): δ = 4.31 (d, J = 3.0 Hz, 2 H), 4.32 (d, J = 7.0 Hz, 2 H), 4.73
(
1
3
Tetrahedron Lett. 1998, 39, 4979. (e) Bruyère, H.;
Ballereau, S.; Selkti, M.; Royer, J. Tetrahedron 2003, 59,
5879.
(s, 1 H), 5.72 (t, J = 7.0 Hz 1 H), 7.21–7.34 (m, 5 H, Ph). C NMR
(62.5 MHz, MeOD): δ = 49.0, 56.6, 82.0, 107.7, 128.1, 128.3,
+
1
29.4, 138.1, 145.6, 160.3, 172.7. HRMS: m/z [M + Na] calcd for
(
5) For cyclizations with NBS, see: (a) Agami, C.; Amiot, F.;
Couty, F.; Dechoux, L. Tetrahedron Lett. 1998, 39, 5373.
(b) Agami, C.; Dechoux, L.; Hebbe, S. Synlett 2001, 1440.
(c) Agami, C.; Dechoux, L.; Hebbe, S.; Moulinas, J.
Synthesis 2002, 79. (d) Agami, C.; Dechoux, L.; Hamon, L.;
Hebbe, S. Synthesis 2003, 859. (e) Banide, E.; Lemau de
Talance, V.; Schmidt, G.; Lubin, H.; Comesse, S.; Dechoux,
L.; Hamon, L.; Kadouri-Puchot, C. Eur. J. Org. Chem. 2007,
4517.
C H NO : 254.0787; found: 254.0789.
1
3
13
3
Compound 6e
1
H NMR (250 MHz, CDCl ): δ = 3.94 (s, 3 H), 4.26 (d, J = 3.0 Hz,
3
2
H), 4.48 (d, J = 6.0 Hz, 2 H), 4.93 (s, 1 H), 5.30 (t, J = 6.0 Hz 1
1
3
H), 6,90 (d, J = 7.0 Hz, 2 H), 7,22 (d, J = 7.0 Hz, 2 H). C NMR
62.5 MHz, CDCl ): δ = 53.8, 56.0, 56.6, 82.0, 107.7, 114.3, 127.0,
(
3
+
127.5, 160.0, 145.6, 160.4, 172.6. HRMS: m/z [M + Na] calcd for
C H NO : 284.0893; found: 284.0896.
1
4
15
4
(
6) (a) Agami, C.; Dechoux, L.; Ménard, C.; Hebbe, S. J. Org.
Chem. 2002, 67, 7573. (b) Alladoum, J.; Dechoux, L.
Tetrahedron Lett. 2005, 46, 8203. (c) Alladoum, J.; Toum,
V.; Hebbe, S.; Kadouri-Puchot, C.; Dechoux, L.
Tetrahedron Lett. 2009, 50, 617.
General Procedure for the Preparation of Compounds 7d,e
To a solution of 5-ylidene-4-amino-2(5H)-furanones 6d,e (0.32
mmol) in CH Cl (2 mL) was successively added SO ·pyridine (65
2
2
3
mg, 0.38 mmol), DMSO (0.4 mL), and Et N (0.4 mL), and the mix-
3
ture was stirred for 4 h. The organic phase was then washed with
©
Georg Thieme Verlag Stuttgart · New York
Synlett 2014, 25, 1713–1716

1716
A. Ear et al.
LETTER
(
7) Toum, V.; Kadouri-Puchot, C.; Hamon, L.; Lhommet, G.;
Mouriès-Mansuy, V.; Vanucci-Bacqué, C.; Dechoux, L.
Synthesis 2011, 2781.
(18) Suresh Dhruva Kumar, D.; Sandhu, J. S. Indian J. Chem.,
Sect. B: Org. Chem. Incl. Med. Chem. 2011, 50, 1479.
(19) (a) Kallikat Augustine, J.; Naik, Y. A.; Mandal, A. B.;
Chowdappa, N.; Praveen, V. B. J. Org. Chem. 2007, 72,
9854. (b) Kallikat Augustine, J.; Naik, Y. A.; Poojari, S.;
Chowdappa, N.; Sherigara, B. S.; Areppa, K. Synthesis
2009, 2349.
(
8) (a) Moore, H. W.; Shelden, R.; Shellhamer, D. F. J. Org.
Chem. 1969, 34, 1999. (b) Moore, H. W.; Shelden, R.;
Deters, D. W.; Wikholm, R. J. J. Am. Chem. Soc. 1970, 92,
1
675. (c) Moore, H. W.; Hernandez, L.; Kunert, D. M.;
Mercer, F.; Sing, A. J. Am. Chem. Soc. 1981, 103, 1769.
(20) (a) McNulty, J.; Steere, J. A.; Wolf, S. Tetrahedron Lett.
1998, 39, 8013. (b) Karchgaudhuri, N.; De, A.; Mitra, A. K.
J. Chem. Res. 2002, 180. (c) Peng, Y.; Song, G. Green
Chem. 2003, 5, 704.
(21) Lu, J.; Toy, P. H. Synlett 2011, 1723.
(22) Balducci, E.; Attolino, E.; Taddei, M. Eur. J. Org. Chem.
2011, 311.
(d) Torres, T.; Shäfer, W. Tetrahedron Lett. 1991, 32, 5825.
(e) Martínez-Díaz, M. V.; Rodríguez-Morgade, S.; Schäfer,
W.; Torres, T. Tetrahedron 1993, 49, 2261. (f) Armesto, D.;
Rodriguez-Morgade, S.; Ortiz, M. J.; Vasquez, P.; Torres, T.
Tetrahedron 1997, 53, 3363.
(
9) Iinuma, H.; Nakamura, H.; Naganawa, H.; Masuda, T.;
Takano, S.; Takeuchi, T.; Umezawa, H.; Iitaka, Y.;
Obayashi, A. J. Antibiot. 1983, 36, 448.
(23) Habrant, D.; Le Roux, A.; Poigny, S.; Meunier, S.; Wagner,
A.; Mioskowski, C. J. Org. Chem. 2008, 73, 9490.
1
1
(
10) (a) Yamamoto, Y.; Ohno, M.; Eguchi, S. Tetrahedron 1994,
(24) We demonstrated by solvent effects in H NMR that the H
NMR chemical shift of the NH proton in (Z)-β-enamino-
diesters is downfielded due to an intramolecular hydrogen
bond, see: Toum, V.; Lhommet, G.; Dechoux, L. Synlett
2012, 2349.
5
0, 7783. (b) For another albeit unsuccessful approach to
basidalin see: Hiyama, T.; Oishi, H.; Suetsugu, Y.; Nishide,
K.; Saimoto, H. Bull. Chem. Soc. Jpn. 1987, 60, 2139.
11) Schachtner, J. E.; Stachel, H. D.; Polborn, K.; Anke, T. Eur.
J. Med. Chem. 1998, 33, 309.
(
(
(
(
(25) Decarboxylated tetronamide 8.
12) (a) Knoevenagel, E. Ber. Dtsch. Chem. Ges. 1898, 31, 2596.
(b) Doebner, O. Ber. Dtsch. Chem. Ges. 1902, 35, 1136.
O
O
13) Collins, P. M.; Overend, W. G.; Shing, T. S. J. Chem. Soc.,
Chem. Commun. 1982, 297.
14) For recent publications concerning the Doebner reaction,
see: (a) Milite, C.; Viviano, M.; Santoriello, M.; Arico, F.;
Sbardella, G.; Castellano, S. RSC Advances 2012, 2, 5229.
BnHN
8
Figure 1
(
b) Varadwaj, G. B. B.; Rana, S.; Parida, K. M. Dalton
Trans. 2013, 42, 5122. (c) Mohite, A. R.; Bhat, R. G. Org.
Lett. 2013, 15, 4564; and references cited therein.
15) (a) Kemme, S. T.; Smejkal, T.; Breit, B. Adv. Synth. Catal.
(26) For a basic dehydrodecarboxylation reaction see:
Thorimbert, S.; Taillier, C.; Bareyt, S.; Humilière, D.;
Malacria, M. Tetrahedron Lett. 2004, 55, 9123.
(27) Parikh, J. R.; v. E. Doering, W. J. Am. Chem. Soc. 1967, 89,
5505.
(
2
008, 350, 989; and references cited therein. (b) For a recent
study concerning the mechanism, see: Bermudez, E.;
Ventura, O. N.; Saenz Mendez, P. J. Phys. Chem. 2010, 114,
1
3086.
(28) Boyer, N.; Gloanec, P.; De Nanteuil, G.; Jubault, P.;
Quirion, J. C. Eur. J. Org. Chem. 2008, 4277.
(29) Tanaka, T.; Oikawa, Y.; Hamada, T.; Yonemitsu, O.
Tetrahedron Lett. 1986, 31, 3651.
(30) Mallinger, A.; Nadal, B.; Chopin, N.; Le Gall, T. Eur. J.
Org. Chem. 2010, 1142.
(
(
16) List, B.; Doehring, A.; Hechavarria Fonseca, M. T.; Wobser,
K.; van Thienen, H.; Rios Torres, R.; Llamas Galilea, P.
Adv. Synth. Catal. 2005, 347, 1558.
17) Lingjian, Z.; Ning, L.; Zhenyuan, M.; Chunquan, S.;
Chunlin, Z.; Jianzhong, Y.; Wannian, Z. Chin. J. Chem.
2
012, 30, 139.
Synlett 2014, 25, 1713–1716
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