Lewis acid catalyzed synthesis of cyclic carbonates, precursors of 1,2- and 1,3-diols

Article abstract of DOI:10.1002/ejoc.201402557

An eco-friendly synthesis of cyclic carbonates through a Lewis acid catalyzed cyclization of tert-butyl carbonates is described. These cyclic carbonates are precursors of 1,2- and 1,3-diols, and the developed method was applied to a short synthesis of a diarylheptanoid, (3S,5S)-alpinikatin.

Full text of DOI:10.1002/ejoc.201402557

SHORT COMMUNICATION
DOI: 10.1002/ejoc.201402557
Lewis Acid Catalyzed Synthesis of Cyclic Carbonates,
Precursors of 1,2- and 1,3-Diols
Johan Cornil,[a] Laurine Gonnard,[a] Amandine Guérinot,[a] Sébastien Reymond,[a] and
Janine Cossy*[a]
Keywords: Iron / Indium / Homogeneous catalysis / Carbonates / Diols / Alpinikatin
An eco-friendly synthesis of cyclic carbonates through a
Lewis acid catalyzed cyclization of tert-butyl carbonates is
described. These cyclic carbonates are precursors of 1,2- and
1,3-diols, and the developed method was applied to a short
synthesis of a diarylheptanoid, (3S,5S)-alpinikatin.
Introduction
As 1,2- and 1,3-diols are ubiquitous units in biologically
active compounds such as polyketide derivatives, a myriad
of methods allowing the diastereoselective preparation of
1,2- and 1,3-diols has been developed[1] and utilized in the
synthesis of natural products.[2] Among them, the stereo-
selective cyclization of allylic and homoallylic tert-butyl
carbonates has emerged as a powerful strategy relying on
asymmetric induction,[3,5] and the resulting cyclic carb-
onates can easily be converted into the corresponding diols
under basic conditions. Since the pioneering work of Bart-
lett et al. in 1982,[4a] halogeno-cyclization providing iodo-
or bromocarbonates has been widely used in total synthesis
to introduce 1,2- as well as 1,3-diol moieties.[6] In contrast,
examples of metal-catalyzed cyclization of allylic and
homoallylic carbonates are still scarce and, to the best of
our knowledge, most of them involve palladium cataly-
sis.[7–9] Thus, an atom-economic and eco-friendly process is
highly desirable to access 1,2- and 1,3-diols via cyclic carb-
onates. Our group has been involved in iron-catalyzed reac-
tions[10] and particularly in the diastereoselective synthesis
of a variety of heterocycles such as piperidines, tetra-
hydropyrans, or isoxazolidines.[10b–10d] Heterocycle forma-
tion implies an iron-induced activation of allylic and/or
benzylic acetate derivatives. Herein, we would like to report
an iron- and/or indium-catalyzed cyclization of tert-butyl
carbonates A providing cyclic carbonates B (Scheme 1).
Scheme 1. Formation of cyclic carbonates from tert-butyl carb-
onates.
Results and Discussion
The cyclization of 1a was first examined, and a variety
of Brønsted and Lewis acids were screened (Table 1). In the
presence of 10 mol-% PTSA·H2O (PTSA = p-toluene-
sulfonic acid) or HCl (2 m in dioxane) in CH2Cl2, the start-
ing material was completely recovered, whereas upon treat-
ment with 10 mol-% TfOH, degradation was observed with
no trace of the desired product (Table 1, entries 1–3). Lewis
acids appeared more powerful than Brønsted acids, as the
use of 10 mol-% FeCl3·6H2O, La(OTf)3, Cu(OTf)2, or
Zn(OTf)2 in CH2Cl2 yielded the cyclic carbonate 2a in 56–
69% NMR yield with a diastereomeric ratio of 70:30 in
favor of the cis-isomer (Table 1, entries 4–7).[11] To our de-
light, when CH2Cl2 was replaced by CH3CN, upon treat-
ment with 10 mol-% FeCl3·6H2O,[12] 2a was formed in 74%
isolated yield and in a diastereomeric ratio of 73:27
(Table 1, entry 8). The best result was obtained in the pres-
ence of 10 mol-% InCl3 as a 92% yield in cyclic carbonate
2a was reached (Table 1, entry 9).[13,14] Thus, these two
Lewis acids were selected to evaluate the scope and limita-
tion of the cyclization of tert-butyl carbonates.
[a] Laboratoire de Chimie Organique, Institute of Chemistry,
Biology and Innovation (CBI) – UMR 8231 – ESPCI
ParisTech/CNRS/PSL* Research University,
10 rue Vauquelin, 75231 Paris Cedex 05, France
E-mail: janine.cossy@espci.fr
The optimized conditions were then applied to the cycli-
zation of homoallylic tert-butyl carbonates 1b–1o (Table 2).
A phenylallylic substituent (R2 = Ph) was found to be
essential to the cyclization, as no conversion was observed
for primary acetate 1b (R2 = H) or for homoallylic
carbonate 1c (R2 = C5H11), regardless of the catalytic sys-
www.lco.espci.fr
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201402557.
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Lewis Acid Catalyzed Synthesis of Cyclic Carbonates
Table 1. Optimization of the cyclization conditions.
The presence of an hydroxy group was found to be detri-
mental to the cyclization, as no trace of the desired product
was observed when 1h was treated with InCl3 (Table 2, en-
try 7).[16] In contrast, an aryl ether was compatible with the
reaction conditions as the InCl3-catalyzed cyclization of 1i
proceeded smoothly, affording the expected carbonate in
79% yield with a 70:30 diastereomeric ratio (Table 2, entry
8).[17] More surprisingly, the presence of a pyridyl ether did
not disrupt the cyclization (Table 2, entry 9). In both pre-
vious examples, it should be highlighted that halogen atoms
were well tolerated, thus offering opportunities for further
functionalization. In addition, an alkyl bromide was also a
suitable substituent, as carbonate 2k was formed in 79%
yield (Table 2, entry 10). Gratifyingly, in the presence of
InCl3, cyclic carbonates 1l and 1m, incorporating an ester
and a phthalimide moiety, respectively, were formed in
moderate to good yields of 54 and 78%, respectively, in a
70:30 and 75:25 cis/trans ratio (Table 2, entries 11 and 12),
respectively.
Entry Solvent
Catalyst
NMR yield[a] cis/trans ratio[b]
1
2
3
4
5
6
7
8
9
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH3CN
CH3CN
PTSA·H2O
TfOH
0%
0%
0%
–
–
–
HCl[c]
FeCl3·6H2O 56%
70:30
70:30
70:30
70:30
73:27
La(OTf)3
Cu(OTf)2
Zn(OTf)2
FeCl3·6H2O 94% (74%)
InCl3
59%
63%
69%
100% (92%) 73:27
[a] Isolated yields in parentheses. [b] Determined by 1H NMR spec-
troscopy on the crude reaction mixture. [c] 2 m in dioxane.
tem used (Table 2, entries 1 and 2).[15] When alkyl-substi-
tuted homoallylic tert-butyl carbonates 1d (R1 = Cy) and
1e (R1 = Me) were treated with 10 mol-% FeCl3·6H2O, the
corresponding cyclic carbonates were isolated in good
yields (82 and 89%, respectively), however with moderate
diastereoselectivities (dr = 75:25 and 71:29, respectively)
(Table 2, entries 3 and 4). A phenyl group can also be toler-
ated, as cyclic carbonate 2f was obtained in 76% yield and
in a 75:25 diastereomeric ratio (Table 2, entry 5). Interest-
ingly, when homoallylic carbonate 1g, derived from a terti-
ary alcohol, was treated with FeCl3·6H2O, the expected cy-
clic carbonate was formed with a good yield of 77%, albeit
with low diastereoselectivity (dr = 60:40) (Table 2, entry 6).
In order to access 1,2-diols, we then turned our attention
to the formation of five-membered-ring carbonates through
allylic carbonate cyclization (Table 3). Upon treatment with
10 mol-% FeCl3·6H2O, allylic carbonates possessing an
alkyl substituent such as 4a (R1 = C9H19) or 4b (R1 = Cy)
delivered the corresponding cyclic carbonates with excellent
yields (98 and 81% for 4a and 4b, respectively) but with
moderate diastereoselectivity in favor of the trans-dia-
stereomer (dr = 63:37 and 65:35, respectively) (Table 3, en-
tries 1 and 2). However, the two diastereomers were sepa-
rated by flash chromatography on silica gel. Disappoint-
ingly, the presence of a phenyl substituent (4c, R1 = Ph) led
to the formation of the deprotected and/or the isomerized
products with no trace of the expected cyclized derivative.
Switching from FeCl3·6H2O to InCl3 did not bring any im-
provement (Table 3, entry 3). This result could be explained
by the presence of two benzylic positions in 4c, both of
which could be activated in the presence of a Lewis acid to
yield a complex mixture of products. When a hydroxy group
was present, such as in 4d, the expected cyclic carbonate
was formed (37%) (Table 3, entry 4) together with tetra-
Table 2. Synthesis of
carbonates.
a
variety of six-membered-ring cyclic
Entry
1
R1
R2
R3
Cat.[a]
2, yield % (dr)[b,c]
1
2
3
4
5
6
7
1b Ph
1c Ph
1d Cy
1e Me
H
C5H11
Ph
Ph
Ph
Ph
Ph
Ph
H
H
H
H
H
Me
H
H
H
H
H
H
[Fe], [In] 2b, 0% (n.d.)
[Fe], [In] 2c, 0% (n.d.)
Table 3. Synthesis of
carbonates.
a variety of five-membered-ring cyclic
[Fe]
[Fe]
[Fe]
[Fe]
[In]
[In]
[In]
[In]
[In]
[In]
2d, 82% (75:25)
2e, 89% (71:29)
2f, 76% (75:25)
2g, 77% (60:40)
2h, 0% (n.d.)
2i, 79% (70:30)
2j, 82% (73:27)
2k, 79% (75:25)
2l, 54% (70:30)
2m, 78% (75:25)
1f Ph
1g C4H9
1h C3H6OH
1i C3H6OAr
1j C3H6OHetAr Ph
1k C3H6Br
1l CO2Et
8[d]
9[d]
10
11
12
Ph
Ph
Entry
4
R1
Cat.[a]
5, yield % (dr)[b],[c]
1m C3H6NHPhth Ph
1
2
3
4
5
6
4a C9H19
4b Cy
4c Ph
4d C3H6OH
4e C3H6OPMB
4f C3H6NTsBoc
[Fe]
[Fe]
[Fe], [In]
[In]
[In]
5a, 98% (63:37)
5b, 81% (65:35)
5c, 0% (n.d.)
[a] [Fe] = FeCl3·6H2O, [In] = InCl3. [b] Isolated yields. [c] Deter-
mined by H NMR spectroscopy on the crude mixture. [d]
1
5d, 37% (75:25), 5Јd[18]
5e, 62% (70:30)
5f, 83% (64:36)
[In]
[a] [Fe] = FeCl3·6H2O, [In] = InCl3. [b] Isolated yields. [c] Deter-
1
.
mined by H NMR spectroscopy on the crude mixture.
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J. Cornil, L. Gonnard, A. Guérinot, S. Reymond, J. Cossy
SHORT COMMUNICATION
hydropyran 5Јd resulting from the nucleophilic attack of the as shown in Scheme 3 for the cyclization of homoallylic
alcohol (25%, dr = 60:40) (Table 3, entry 4).[18] Protection carbonates (TS I vs. TS II). However, the ability of
of the alcohol as a PMB ether (4e) significantly improved FeCl3·6H2O to induce the epimerization of 2,6-piperidines
the yield of the cyclic carbonate (62%) (Table 3, entry 5). or 2,6-tetrahydropyrans by a re-opening process has already
A protected amine is also tolerated under these reaction been highlighted,[9] and, as a consequence, the hypothesis
conditions, as carbonate 5f was isolated in 83% yield with of a thermodynamic control could not be completely ruled
a diastereomeric ratio of 64:36 (Table 3, entry 6).
In order to ensure the easy formation of 1,3- and 1,2-
diols from cyclic carbonates, 2a (dr = 70:30) was treated
with K2CO3 in MeOH. As expected, the corresponding
1,3-diol 3a was isolated in quantitative yield with no modi-
fication of the diastereomeric ratio (Scheme 2). Similarly,
carbonate cis-5b was easily transformed into 1,2-diol 3b
(Scheme 2).
out.
Scheme 3. Hypothetical origin of diastereoselectivity under kinetic
control.
In order to illustrate the potential of our method, we
embarked on a short synthesis of (3S,5S)-alpinikatin
(Scheme 4), which was recently extracted from the seeds of
Alpinia katsumadai.[20] (3S,5S)-Alpinikatin is part of the di-
Scheme 2. Preparation of 1,3- and 1,2-diols.
Considering our previous mechanistic studies on iron- arylheptanoid family, which includes more than 300 mol-
catalyzed heterocyclizations,[10] we suggest that an allylic ecules exhibiting attractive biological properties.[21] From a
carbocation intermediate is formed during the reaction. structural point of view, (3S,5S)-alpinikatin possesses a 1,3-
When the InCl3-catalyzed cyclization of 1e was monitored diol motif that could come from a homoallylic carbonate
1
by H NMR spectroscopy, no change in the diastereomeric through the developed indium-catalyzed cyclization fol-
ratio was observed, which suggests a kinetic control.[19] The lowed by methanolysis. The synthesis started with the pro-
diastereoselectivities could be explained by the minimi- tection and subsequent reduction of methyl 3-(4-
zation of the steric interactions in the transition state hydroxyphenyl)propionate to provide the corresponding
Scheme 4. Total synthesis of (3S,5S)-alpinikatin.
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Lewis Acid Catalyzed Synthesis of Cyclic Carbonates
Ferrié, L. Boulard, F. Pradaux, S. Bouzbouz, S. Reymond, P.
Capdevielle, J. Cossy, J. Org. Chem. 2008, 73, 1864.
For a review on organic carbonates, see: A.-A. G. Shaikh,
Chem. Rev. 1996, 96, 951.
aldehyde. An enantioselective allyltitanation with the
Duthaler–Hafner complex (S,S)-Ti-I[22] was then performed
to afford the expected homoallylic alcohol 6 with good yield
and enantiomeric excess (ee Ͼ 90%). A cross-metathesis
with 1-phenylallyl acetate in the presence of the Grubbs II
catalyst (GII) and CuI[23] furnished 7, which was trans-
formed into carbonate 8 upon treatment with Boc2O. When
this homoallylic carbonate was treated with 10 mol-%
InCl3, the corresponding cyclic product was isolated with a
good yield of 81% albeit with a moderate diastereoselecti-
vity of 73:27 in favor of the cis-isomer. Flash chroma-
tography on silica gel allowed a partial separation of the
two diastereomers, and a pure sample of the cis-compound
was isolated. Finally, the use of K2CO3 in MeOH provided
(3S,5S)-alpinikatin through carbonate methanolysis and de-
protection of the phenolic group.
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[5]
[6]
Conclusions
In summary, we have developed a new approach to five-
and six-membered-ring cyclic carbonates by a Lewis acid
catalyzed cyclization of allylic and homoallylic tert-butyl
carbonates. In most examples, the reaction proceeds with
high yields and moderate diastereoselectivities. The cheap
FeCl3·6H2O with its low toxicity can be used as a catalyst
for the cyclization, but InCl3 was preferred when functional
groups were present. The synthesized carbonates can easily
be transformed to the corresponding 1,2- and 1,3-diols, and
the method has been successfully applied to the total syn-
thesis of a natural product, (3S,5S)-alpinikatin.
[7]
Experimental Section
[8]
[9]
For an indium-promoted synthesis of carbonates, see: M. Lom-
bardo, F. Pasi, C. Trombini, Eur. J. Org. Chem. 2006, 3061.
Typical Procedure for Lewis Acid Catalyzed Cyclization of Allylic
and Homoallylic Carbonates: To a solution of the tert-butyl carb-
onate A (1 equiv.) in CH3CN (0.1 m) was added FeCl3·6H2O
(0.1 equiv.) or InCl3 (0.1 equiv.). The resulting mixture was stirred
for 24 h at room temp., and the crude mixture was concentrated
under reduced pressure. Flash chromatography on silica gel af-
forded the desired cyclic carbonates B.
Gold-catalyzed rearrangement of propargylic tert-butyl
carbonates has been well documented, see for example: a) A.
Buzas, F. Gagosz, Org. Lett. 2006, 8, 515; b) C. Lim, J.-E.
Kang, J.-E. Lee, S. Shin, Org. Lett. 2007, 9, 3539; c) A. K.
Buzas, F. M. Istrate, F. Gagosz, Tetrahedron 2009, 65, 1889; d)
J.-E. Kang, S. Shin, Synlett 2006, 717.
a) B. Anxionnat, A. Guérinot, S. Reymond, J. Cossy, Tetrahe-
dron Lett. 2009, 50, 3470; b) A. Guérinot, A. Serra-Muns, C.
Gnamm, C. Bensoussan, S. Reymond, J. Cossy, Org. Lett.
2010, 12, 1808; c) A. Guérinot, A. Serra-Muns, C. Bensoussan,
S. Reymond, J. Cossy, Tetrahedron 2011, 67, 5024; d) J. Cornil,
A. Guérinot, S. Reymond, J. Cossy, J. Org. Chem. 2013, 78,
10273.
[10]
Supporting Information (see footnote on the first page of this arti-
cle): Experimental procedures, characterization data and copies of
1H NMR and 13C NMR spectra.
Acknowledgments
[11]
[12]
The same results were obtained with anhydrous FeCl3 and
FeCl3·6H2O, and the latter was preferred as it was easier to
handle.
FeCl3·6H2O was purchased from Sigma–Aldrich (purity 97%,
Cu Ͻ 0.003%, Zn Ͻ 0.003%).
Agence Nationale de la Recherche (ANR) is thanked for financial
support.
[13]
[14]
InCl3 was purchased from Sigma–Aldrich (98%).
Surprisingly, in CH2Cl2, the use of InCl3 (10 mol-%) led to
poor conversion of 1a (17%).
The reactions became sluggish, and the sole new product ob-
served resulted from a cleavage of the Boc group. Increasing
the temperature to 50 or 120 °C under microwave irradiation
did not improve the result.
Nucleophilic attack of the hydroxy group took place, delivering
the seven-membered ring with no diastereoselectivity in 50%
yield; see Supporting Information for more details.
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[2] Our group has been involved in the synthesis of natural prod-
ucts possessing 1,3-diol moieties, see for example: a) S. Bouz-
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[15]
[16]
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SHORT COMMUNICATION
[17] Compound 2j was formed in 36% yield in the presence of
FeCl3·6H2O.
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[18] See Supporting Information for details.
[19] The same experiment could not be monitored in the presence
of FeCl3·6H2O, as the reaction proved to be too fast.
[20] J. W. Nam, G. Y. Kang, A. Han, D. Lee, Y. Lee, E. Seo, J. Nat.
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Received: May 13, 2014
Published Online: July 11, 2014
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Eur. J. Org. Chem. 2014, 4958–4962