An intramolecular journey of a carboxyl group around 1,2-dihydropyridines: multisite δ- versus γ-lactonization reactions

Article abstract of DOI:10.1016/j.tetlet.2009.10.038

In contrast to substituted 4-acetic acid 1,4-dihydropyridines, giving only δ-lactones upon intramolecular reactions, 2-substituted 1,2-dihydropyridines led, besides to δ-lactones, also to new, structurally interesting γ-lactones as the result of a bromine

Full text of DOI:10.1016/j.tetlet.2009.10.038

Tetrahedron Letters 50 (2009) 7274–7279
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
An intramolecular journey of a carboxyl group around 1,2-dihydropyridines:
multisite d- versus c-lactonization reactions
Andrée Parlier a, Catherine Kadouri-Puchot a, Sandra Beaupierre a, Nathalie Jarosz a, Henri Rudler a,
,
*
Louis Hamon a, Patrick Herson a, Jean-Claude Daran b
a Institut Parisien de Chimie Moléculaire UMR CNRS 7201, Université Pierre et Marie Curie, CC 47, 4 Place Jussieu 75252 Paris Cedex 5, France
b Laboratoire de Chimie de Coordination, 205 Route de Narbonne 31077 Toulouse Cedex 4, France
a r t i c l e i n f o
a b s t r a c t
Article history:
In contrast to substituted 4-acetic acid 1,4-dihydropyridines, giving only d-lactones upon intramolecular
reactions, 2-substituted 1,2-dihydropyridines led, besides to d-lactones, also to new, structurally interest-
Received 7 September 2009
Revised 2 October 2009
Accepted 7 October 2009
Available online 31 October 2009
ing
c-lactones as the result of a bromine-induced carbon-carbon double bond ‘Umpolung’.
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
1,2-Dihydropyridines
Lactones
Ring-closing/ring-opening
Rearrangements
Synthetic methods
1. Introduction
of dihydropyridines A, and to the presence in the substrate of a
directing group, a polarized ene-carbamate, the lactonization reac-
tions led only to one type of lactones, d-lactones B, and as expected
for substrates containing the double bond within a ring, with com-
plete stereocontrol. The acid-promoted ring-opening reactions of
lactones B led stereoselectively to the dihydropyridines C. For
R = H in C, re-lactonization reactions involving only the substituent
at C-2 occurred to give D regioselectively.
The purpose of the present Letter is to describe an even more
complex trip of the carboxyl group, starting from C-2-functional-
ized 1,2-dihydropyridines, giving upon halolactonizations inter
alia, new fluorolactones, interesting on a biological point of view,
and upon unexpected bromolactonizations/solvolytic rearrange-
ments, piperidinelactones, precursors of azasugars.
The applications of dihydropyridines have already a long and
interesting history due to their involvement as fundamental reduc-
ing agents in living systems, a property which was mimetically ex-
tended to organic1 and even to organometallic chemistries.2 Last
but not the least, dihydropyridines are also highly valuable and
nowadays essential in pharmaceutical sciences: they are part of
the chemist’s range of tools for the synthesis of highly elaborate
molecules. Yet, their non-biomimetic transformations, mainly
developed by Lavilla et al.,3 emerged also as part of important stra-
tegic starting material in organic synthesis. Inspired by the use of
bis (TMS) ketene acetals as dinucleophiles for the synthesis of a
broad range of c
-lactones,4 we also focused our attention these last
few years on the transformations of pyridines via dihydropyri-
dines, according to such a route.5
2. Results
Intramolecular reactions induced by electrophiles allowed us in-
deed to synthesize, starting from C-4 acetic acid derived 1,4-dihy-
dropyridines A (Fig. 1), a broad range of tetrahydropyridine- and
piperidine-fused lactones B and D and especially fluorolactones
(e.g., X = F in B) of biological relevance.6 The key transformations re-
lied on easy, stereoselective cascade ring-closing to B, ring-opening
toC, and ring-closingreactionsto D, leadingtotwotypes of products,
d-lactones B and D, as summarized in Figure 1. Due to the symmetry
2.1. Fluorolactones and hydroxylactones
Although C-2-functionalized dihydropyridines can be obtained
upon the interaction of ketene acetals with activated pyridines, the
reaction suffers from two drawbacks: either, mixtures of C-2 and
C-4 regioisomers were formed, depending on the substituent on
the pyridine-ring, or the selective C-2 regioisomer was observed
only in limited cases, for example, with the non-substituted ketene
acetal 1 (R1 = R2 = H).5b However, we found that the C-4 t-Bu-substi-
tuted pyridine was the substrate of choice for the introduction of
* Corresponding author. Tel.: +33 (0)144275092; fax: +33 (0)144273787.
E-mail address: henri.rudler@upmc.fr (H. Rudler).
0040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2009.10.038

A. Parlier et al. / Tetrahedron Letters 50 (2009) 7274–7279
7275
R2
O
R2
R2
R2
O
O
R1
R1
R1
O
X
R1
OH
OH
X+
OH
R= H
OR
X= H
O
O
O
O
N
N
N
N
R4
R4
MeOOC
R3
COOMe
MeOOC
COOMe
R3
A
B
C
D
Figure 1. Ring-closing and ring-opening reactions of 1,4-dihydropyridines.
substituents in C-2, and thus for the selective synthesis of 1,2-dihy-
dropyridines (Scheme 1).
The hydroxylactonization reactions carried out on 3a,b by
means of m-chloroperbenzoic acid led to a single compound 6a,b
which could again be fully characterized by NMR experiments
and by a single crystal structure determination on 6b (Fig. 3) as
C-4 lactonization products.9
Thus, the ketene acetals R1R2C@C(OSiMe3)2 1a,b (R1 = R2 = Me
and R1R2 = (CH2)5) reacted with 4 t-Bu pyridine 2 in the presence
of triflic anhydride to give selectively the corresponding 1,2-addi-
tion products 3a (98%, white solid, mp 118 °C) and 3b (56%, white
solid, mp 178 °C). The interaction of Selectfluor (1-chloromethyl 4-
fluoro-1,4-diazoniabicyclo (2.2.2) octane bis (tetrafluoroborate))7
with 3a and 3b led in each case to two compounds 4a,b and
5a,b, respectively, in 46% and 65% overall yields and separable by
column chromatography (Scheme 2).
2.2. Bromolactones
Three approaches were used for the bromolactonization reac-
tion of 3a,b,10 the two classical one’s involving N-bromosuccini-
mide, and a more unusual one, using copper bromide. Under
classical kinetic conditions, with NBS in ice-cold dichloromethane,
in the presence of sodium hydrogenocarbonate, a single, rather
unstable product formed rapidly from 3a. Its NMR data taken after
half an hour of reaction were in agreement with structure 9a and
were very close to those of fluorolactones 4. Indeed, the 1H NMR
spectrum disclosed signals at d 6.66 and 5.43 ppm again as a dou-
blet (J = 10 Hz) and a doublet of doublets (J = 10, 2.5 Hz), at d 4.72, t,
J = 2.5 Hz) and at d 4.28 ppm (d, J = 2.5 Hz). After one night at room
temperature, 9a could only be detected in trace amounts. Besides,
two new products, the 1H NMR data of which were in agreement
with those of 7a and 8a were observed.
Especially significant were the 1H NMR data of 4b showing up
two doublets at d 6.70 and 5.53 ppm (J = 8.5 Hz) for H-7 and H-8,
a multiplet at d 5.35 ppm for H-9 (ddd, J = 46.5, 3.5 and 2 Hz),
and a multiplet at d 4.38 (dd, J = 7 and 3.5 Hz) for H-5, the presence
of fluorine being established by 19F NMR with signals at d À73.6 (d,
J = 20 Hz) and À215.2 (dqt, J = 46, 16, 2 Hz), respectively, for the
fluorine of the triflate and the fluorine of the lactone.
Confirmation of the structure of these C-4 cyclization products
came from an X-ray analysis carried out on 4a (Fig. 2).8
The same mixture of products was obtained, respectively, in
67% and 45% yields from 3a,b when the reaction was carried out
under thermodynamic conditions, using NBS in anhydrous dichlo-
romethane as a source of Br+. According to their NMR data these
products differed only by the position of the introduced bromine.
Their structure, as C-6 lactonization products, was ascertained by
an X-ray analysis carried out on 7b (Fig. 4).11 This also confirmed
the stereochemical outcome of these reactions. Finally, the interac-
tion of 3a,b with CuBr2 on Al2O3 as a source of ‘electrophilic’ bro-
R1
OSiMe3
4
R2
O
5
OSiMe3
3
OH
R2
1
1'
6
2
N
1
N
R1
SO2CF3
Tf2O
1a R1=R2= Me
1b R1R2= (CH2)5
mine, in refluxing chloroform,12 gave in each case
a single
2
3a 98%
3b 56%
product, stable with respect to the purification conditions (silica
gel column chromatography), the physical data of which were in
all respect identical to those of 7a and 7b (Scheme 3).
Scheme 1. Synthesis of dihydropyridines 3. Reagent and conditions: CH2Cl2, 0 °C to
rt, 17 h.
7
1
X
X
8
6
5
O
9
i
8
O
OH
R2
ii
O
O
N
Tf
O
3
4
3
7
1
5
R2
N
N
R2
R1
4
R1
R1
Tf
SO2CF3
3a
X=F 4a 40%
X=F 4b 39%
X=OH 6a 42%
X=OH 6b 26%
5a 6%
3b
5b 26%
Scheme 2. Synthesis of fluoro- and hydroxylactones. Reagents and conditions: (i) X = F selectfluor, CH3CN, NaHCO3, rt, 17 h.; (ii) X = OH m-chloroperbenzoic acid, CH2Cl2, rt,
3 d.

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A. Parlier et al. / Tetrahedron Letters 50 (2009) 7274–7279
Figure 2. X-ray structure of compound 4a.
Figure 3. X-ray structure of compound 6b.
2.3. Solvolysis reactions of bromolactones 7: formation of new
c-lactones
c-lactones 10b and 11b, respectively, in 91% and 94% yields
(Scheme 4).
Their structure was again ascertained both by NMR and by an
X-ray analysis carried out on 10b (Fig. 5)13 confirming the presence
of a -lactone, and of a trisubstituted double bond. It is interesting
to notice here, as far as its straightforward synthesis is concerned,
that compounds 10b could be obtained directly and almost quan-
titatively during the interaction of dihydropyridine 3b with CuBr2
in the presence of ethanol-stabilized CHCl3.
Although stable on silica gel, compounds 7 underwent surpris-
ing but, as far as the resulting structures are concerned, highly
rewarding solvolysis reactions. These reactions were easy and fast
in the case of alcohols, taking place at room temperature, but oc-
curred slower and under more drastic conditions in the case of
water. Thus, the interaction of 7b with alcohols (MeOH or EtOH)
at room temperature led to new types of lactones, for the first time
c
Figure 4. X-ray structure of compound 7b.

A. Parlier et al. / Tetrahedron Letters 50 (2009) 7274–7279
7277
7
i
4
7
1
Br
Br
Br
8
6
5
6
O
ii
iii
5
8
8
3
O
O
O
OH
R2
O
O
O
N
Tf
3
3
4
3
4
1'
6
1
1
7
5
5
2
N
N
N
9
R2
Me
1
R2
4
R1
Tf
R1
R1
Tf
Tf
3a, 3b
Me
7a
7b
8a 8b
9a
i
0% 0%
0% 0%
27% 23%
0% 0%
100%
0%
ii 40% 22%
iii 70% 76%
0%
Scheme 3. Synthesis of bromolactones. Reagents and conditions: (i) NBS, NaHCO3, CH2Cl2, 0 °C, 1 h; (ii) NBS, CH2Cl2, rt, 17 h; (iii) CuBr2, Al2O3, ethanol free CHCl3, 65 °C, 36 h.
Br
R'OH
O
O
O
O
N
Tf
R'O
N
R'= Et, Me, H
Tf
7b
10b R'=Et 91%
11b R'=Me 94%
12b R'=H 32%
Scheme 4. Solvolysis reactions of bromolactone 7b.
Similarly, bromolactone 7b reacted with water in refluxing THF
to give the corresponding alcohol 12b in 32% yield. However, no
reaction was observed between 8b and MeOH, even under reflux.
3. Discussion
Figure 5. X-ray structure of compound 10b.
Starting from cationic species, resulting from the interaction of
an electrophile with the dihydropyridines, a rationale for all of
these transformations, based on calculations and previous results
in the field can be suggested. The calculations of the structures
and energies of the different species were performed using the
semiempirical AM1 Hamiltonian in the AMPAC14 or GAMESS15
suite of programs. The structures of the different cations were first
optimized in the AMPAC using the default BFGS Algorithm
minimizing the gradient norm. Ab initio calculations for some spe-
cies were also performed using STO3G or 631G atomic basis using
GAMESS. Atomic charges have been calculated using the Mulliken
Population Analysis.16 These calculations were run on RS/6000 Sys-
tem Regatta Power 4 machines.
of lactones was expected, the reaction taking place also under ther-
modynamic conditions. However, on one hand the nature of the
intermediates formed with that reagent might be questioned since
in the case of 2-methyldihydropyridine, products arising rather
from a radical reaction were observed.17On the second hand, the
conditions of the reaction are quite different.
As far as the other electrophiles are concerned and according to
the literature data, and our previous conclusions, F+ reacting with
dihydropyridines 3a,b leads to the formation, in the first irrevers-
ible step, of a kinetic product therefore upon the addition of fluo-
rine to carbon C-3.17,18 A syn-addition of the corresponding
counterion of Selecfluor, or the direct formation of carbocationic
species might then occur either at C-4 (stabilization by the t-Bu
group but b-destabilization by fluorine)19 or at C-6 (stabilization
by the nitrogen atom). An intramolecular substitution (or addition)
would then result in the formation of the two observed and more
stable products 4 and 5 in agreement with the calculated data.
The formation of piperidinelactones 10–12 might be ascribed to
a concerted, alcohol-mediated opening of the lactone-ring to the
iminium H, addition of an alcoholate exclusively to the less hin-
dered face of the intermediate H trans to Br, to give I. This is fol-
In the case of Br+, under kinetic control, the addition of the
halide occurs at C-3, which is also the more negatively charged car-
bon (Fig. 7). The intermediate cation E is stabilized both by the t-Bu
group and by the introduced bromine (in the form of a bridged bro-
monium ion) (Fig. 6).
Moreover, the bromination being very fast and reversible, the
structure of the final product will only be dependent on the site
of interaction of the carboxylate, where the more positive charge
is, thus at C-4 as in E, giving 9. The transformation of dihydropyr-
idine 3 into lactone 9 being reversible, it might give back, as inter-
mediates the bridged bromonium ions F and G.
lowed by a highly thermodynamically favorable
c-lactonization
The intramolecular ring-closing reaction would then provide
the observed thermodynamically more stable bridging lactones 7
and 8, in agreement with calculations and previous observations.5d
The formation of a single product during the interaction of CuBr2
with dihydropyridines 3 is somewhat surprising, since a mixture
reaction to 10 (Fig. 8).
That, however, no reaction was observed between 8b and
MeOH, even under reflux, can be inferred to a more favorable
intramolecular ring-closing reaction: even if the lactone-ring
would open to give the iminium J, no reaction with an external

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A. Parlier et al. / Tetrahedron Letters 50 (2009) 7274–7279
R
R
R
Br
Br
Br+
OH
O
3
O
Br
OH
OH
O
N
N
N
R2
R1
R2
R1
R2
R1
Tf
Tf
Tf
E
F
G
R
R
R
ßr
Br
Br
O
O
O
O
N
O
N
O
N
Tf
R2
R2
R2
R1
Tf
Tf
R1
R1
7
8
9
Figure 6. Bromolactonizations of dihydropyridines 3: mechanistic aspects.
tBu
-0.059
H
H
-0.237
-0.175
-0.115
COOH
H
N
-0.912
Tf
tBu
tBu
tBu
H
X
X
X
H
COOH
COOH
COOH
N
N
N
Tf
Tf
Tf
X= Br
X= F
-107.28
-141.95
tBu
-100.97
-135.39
tBu
-98.00
-133.91
tBu
Br
Br
Br
OH
O
N
Tf
H
O
N
Tf
O
N
Tf
OH
OH
-263.02
tBu
-267.63
tBu
-259.69
tBu
Br
Br
Br
O
O
N
Tf
H
O
N
Tf
O
N
Tf
O
O
-96.23
-93.69
-94.00
Figure 7. Respective charge distributions on substituted 1,4-dihydropyridines and formation enthalpies of the carbocationic species obtained therefrom.
nucleophile would take place, since the reverse reaction, giving
back the starting lactone, is, according to our previous observa-
tions, highly favoured6d (Fig. 9). Such a result is also supported
by the calculations which indeed confirm that among the bromo-
lactones 8b is thermodynamically the most stable.
4. Conclusions
As a conclusion, it appears that functionalized 1,2-dihydropyri-
dines such as those described herein are the precursors of choice
for the synthesis of diversely tetrahydropyridine-fused lactones,

A. Parlier et al. / Tetrahedron Letters 50 (2009) 7274–7279
7279
R
R
R
Br
Br
O
R'OH
R'O
O
O
O
7
H
R2
R'O
N
N
R'O
N
O
OH
R1
R2
R2
R1
R1
Tf
Tf
Tf
H
I
10, 11, 12
Figure 8. Solvolysis rearrangement reactions of bromolactones 7.
2. (a) Rudler, H.; Audouin, M.; Parlier, A.; Martin-Vaca, B.; Goumont, R.; Durand-
Réville, T.; Vaissermann, J. J. Am. Chem. Soc. 1996, 118, 12045–12058; (b)
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Audouin, M.; Certal, V.; Vaissermann, J. Tetrahedron 2000, 56, 5001–5027; (d)
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Lavilla, R.; Baron, X.; Coll, O.; Gullon, F.; Masdeu, C.; Bosch, J. J. Org. Chem. 1998,
63, 10001–10005. and references cited therein.
R
R
Br
Br
O
O
N
O
N
OH
R2
Tf
R2
Tf R1
R1
8b
J
4. Bellassoued, M.; Chelain, E.; Collot, J.; Rudler, H.; Vaissermann, J. J. Chem. Soc.,
Chem. Commun. 1999, 187–189.
Figure 9.
5. (a) Rudler, H.; Denise, B.; Parlier, A.; Daran, J.-C. Chem. Commun. 2002, 940–941;
(b) Rudler, H.; Denise, B.; Xu, Y.; Parlier, A.; Vaissermann, J. Eur. J. Org. Chem. 2005,
3724–3744; (c) Garduno-Alva, A.; Xu, Y.; Gualo-Soberanes, N.; Lopez-Cortes, J.;
Rudler, H.; Parlier, A.; Ortega-Alfaro, M. C.; Alvarez-Toledano, C.; Toscano, R. A.
Eur. J. Org. Chem. 2008, 3714–3723; (d) Xu, Y.; Rudler, H.; Denise, B.; Parlier, A.;
Chaquin, P.; Herson, P. Tetrahedron Lett. 2006, 47, 4541–4544.
O
R1
R2
OH
b
6. (a) Lourie, L. F.; Serguchev, Y. A.; Shevchenko, G. V.; Ponomenko, M. V.;
Chernega, A. N.; Rusanov, E. B.; Howard, J. A. K. J. Fluorine Chem. 2006, 127, 377–
385; (b) Meng, W.-D.; Qing, F.-L. Curr. Top. Med. Chem. 2006, 6, 1499–1528; (c)
Smart, B. E. J. Fluorine Chem. 2001, 109, 3–11; (d) Bégué, J. P.; Bonnet-Delpon, D.
Chimie bioorganique et médicinale du fluor; EDP Sciences/CNRS: Paris, 2005.; (e)
Singh, R. P.; Shree, J. M. Acc. Chem. Res. 2004, 37, 31–34; (f) O’Hagan, D. Chem.
Soc. Rev. 2008, 37, 308–319.
a
c
R
H
N
7. (a) Banks, R. E.; Murtagh, V.; Tsiliopoulous, E. J. Fluorine Chem. 1991, 52, 389–
401; (b) Lal, G. S. J. Org. Chem. Soc. 1993, 58, 2791–2796; (c) Singh, R. P.;
Tf
Shreeve, J. M. Acc. Chem. Res. 2004, 37, 31–44.
ꢀ
8. Crystal data for 4a: C14H19F4NO4S, M = 373.09
,
triclinic, space group P1,
Figure 10. Observed ring-closure sites of 1,2-dihydropyridines 3.
a = 6.2206(18) Å, b = 11.368(2) Å, c = 13.016(4) Å, V = 838.6(4) Å3, Z = 2, (MoK
a
,
k = 0.71073) T = 200 K, R1, wR2 [I > 2r(I)] = 0.0540, R1, wR2 (all data) = 0.169.
CCDC 717522.
9. Crystal data for 6b: C17H24F3NO5S, M = 474.333, monoclinic, space group Cc,
a = 10.0005(8) Å, b = 17.8028(16) Å, c = 10.8951(12) Å, V = 1907.2(3) Å3, Z = 4,
the reaction conditions promoting a series of ring-closing/ring-
opening/ring-closing transformations and directing the sites of
the lactonization reactions.
Dc = 1.43 g cmÀ3
0.100. CCDC 738889.
10. For review on halolactonization reactions, see: Ranganathan, S.;
, (VoKa, k = 0.71073) T = 200 K, R1, wR2 [I > 2r(I)] = 0.046,
a
The formation of piperidinelactones 10–12 via the route c in
only a few high-yielding steps from pyridine, besides the expected
d-lactones via the routes a and b (Fig. 10), is very interesting on a
synthetic point of view since they can be considered as valuable
and close starting materials for the synthesis of azasugars.20
Muraleedharan, K. M.; Vaish, N. K.; Jayaraman, N. Tetrahedron 2004, 60,
5273–5308. and references cited therein.
11. Crystal data for 7b: C16H23BrF3NO4S, M = 474.333, hexagonal, space group P65,
a = 10.3064(2) Å, b = 10.3064(2) Å, c = 33.2508(14) Å, V = 3058.77(15) Å3, Z = 6,
Dc = 1.496 g cmÀ3, (VoK
a, k = 0.71073) T = 180 K, R1, wR2 [I > 2r(I)] = 0.0367,
0.0831. CCDC 717647.
12. Rood, G. A.; DeHaan, J. M.; Zibuck, R. Tetrahedron Lett. 1996, 37, 157–158.
13. Crystal data for 10b: C19H28F3NO5S, M = 399.132, monoclinic, space group P21/
n, a = 11.1055(14) Å, b = 10.7290(8) Å, c = 19.388(2) Å, V = 2216.6(4) Å3, Z = 4,
Supplementary data
(VoKa, k = 0.71073) T = 200 K, R1, wR2 [I > 2r(I)] = 0.040. CCDC 717523.
14. Schmidt, M. W.; Baldridge, K. K.; Boatz, J. A.; Elbert, S. T.; Gordon, M. S.; Jensen,
J. J.; Koseki, S.; Matsunaya, N.; Nguyen, K. A.; Su, S.; Windus, T. L.; Dupuis, M.;
Montgomery, J. A. J. Comput. Chem. 1993, 14, 1337–1363.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.tetlet.2009.10.038.
15. Dewar, M. J. S.; Zoebisch, E. G.; Healy, E. F.; Stewart, J. J. P. J. Am. Chem. Soc.
1985, 107, 3902–3909.
16. Mulliken, R. S. J. Chem. Phys. 1955, 23, 1833–1840.
References and notes
17. Rudler, H.; Parlier, A.; Hamon, L.; Herson, P.; Chaquin, P.; Daran, J.-C.
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18. Rudler, H.; Parlier, A.; Hamon, L.; Herson, P.; Daran, J.-C. Chem. Commun. 2008,
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