Cyclizative atmospheric CO2 fixation by unsaturated amines with t-BuOI leading to cyclic carbamates

Article abstract of DOI:10.1021/ol302201q

A cyclizative atmospheric CO₂ fixation by unsaturated amines such as allyl and propargyl amines under mild reaction conditions, efficiently leading to cyclic carbamates bearing a iodomethyl group, have been developed utilizing tert-butyl hypoiodite (t-BuOI).

Full text of DOI:10.1021/ol302201q

ORGANIC
LETTERS
2012
Vol. 14, No. 18
4874–4877
Cyclizative Atmospheric CO2 Fixation by
Unsaturated Amines with t‑BuOI Leading
to Cyclic Carbamates
Youhei Takeda,†,‡ Sota Okumura,† Saori Tone,† Itsuro Sasaki,† and Satoshi Minakata*,†
Department of Applied Chemistry and Frontier Research Base for Global Young
Researchers, Graduate School of Engineering, Osaka University, Yamadaoka 2-1, Suita,
Osaka 565-0871, Japan
minakata@chem.eng.osaka-u.ac.jp
Received August 8, 2012
ABSTRACT
A cyclizative atmospheric CO2 fixation by unsaturated amines such as allyl and propargyl amines under mild reaction conditions, efficiently
leading to cyclic carbamates bearing a iodomethyl group, have been developed utilizing tert-butyl hypoiodite (t-BuOI).
Control of the concentration level of carbon dioxide, a
notorious greenhouse gas, in the atmosphere has been a
worldwide issue to be solved urgently.1 To address the
issue, there are two main types of approaches: CO2 capture
and storage/sequestration (CCS); CO2 capture and its
utilization (CCU).2 The former approach is based on the
idea of capturing CO2 into adsorbents such as solid, liquid,
and membranes.3 On the other hand, the CCU approach
would allow for not only consuming CO2 but also produ-
cing value-added chemicals by synthetic methods from
abundant and environmentally friendly C1 feedstock.
Nevertheless, the biggest obstacle to this approach lies in
the thermodynamic stability of CO2, which is at the highest
oxidation state of carbon. To activate CO2, harsh reaction
conditions such as the use of external strong acids/bases, or
high pressures, have been utilized.2,4 Therefore, the devel-
opment of chemical transformation methods of CO2 with-
out energy-consuming processes is desired. In this regard,
we have developed an atmospheric CO2 fixation method
by allyl alcohols under mild reaction conditions utilizing
tert-butyl hypoiodite (t-BuOI).5 The key to success was the
use of a powerful iodinating reagent (t-BuOI),6,7 which
readily reacts with carbonic acid monoalkyl esters
((allyl)OC(O)OH)) generated from the reaction of CO2
and allyl alcohols, thereby exchanging the acidic proton
with iodine leading to cyclic carbonate products. The only
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Catal. Today 2006, 115, 33. (f) Behr, A. Angew. Chem., Int. Ed. Engl.
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Ed. 2012, 51, 7804. (b) Minakata, S.; Okumura, S.; Nagamachi, T.;
Takeda, Y. Org. Lett. 2011, 13, 2966. (c) Minakata, S.; Morino, Y.; Ide,
T.; Oderaotoshi, Y.; Komatsu, M. Chem. Commun. 2007, 3279.
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2006, 8, 3335. (e) Minakata, S.; Morino, Y.; Oderaotoshi, Y.; Komatsu,
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† Department of Applied Chemistry.
‡ Frontier Research Base for Global Young Researchers.
(1) (a) Olah, G. A.; Goeppert, A.; Prakash, G. K. S. Beyond Oil and
Gas: The Methanol Economy, 2nd ed.; Wiley-VCH: Weinheim, Germany,
2009. (b) Bakker, D.; Watson, A. Nature 2001, 410, 765. (c) Abelson, P. H.
Science 2000, 289, 1293.
(2) Yang, Z.-Z.; He, L.-N.; Gao, J.; Liu, A.-H.; Yu, B. Energy
Environ. Sci. 2012, 5, 6602.
(3) (a) D’Alessandro, D. M.; Smit, B.; Long, J. Angew. Chem., Int.
Ed. 2010, 49, 6058. (b) Wang, Q.; Luo, J.; Zhong, Z.; Borgna, A. Energy
Environ. Sci. 2010, 4, 42. (c) Choi, S.; Drese, J. H.; Jones, C. W.
ChemSusChem 2009, 2, 796 and references cited therein.
r
10.1021/ol302201q
Published on Web 08/31/2012
2012 American Chemical Society

byproduct formed in this reaction is nontoxic alcohol
(t-BuOH), which would not interfere with the progression
of the reaction. However, due to the existence of a highly
reactant-favored equilibrium between two systems of CO2/
allyl alcohols and carbonic acid monoalkyl esters (Scheme 1),
2 equiv of t-BuOI were required to obtain products in high
yields. Contrary to the system, amines including allyl amines
have been known to be good capturing agents for CO2 to
form carbamic acids or ammonium carbamates owing to
their higher nucleophilicities than alcohols.8 Utilization of
the thermodynamically favored process in two cyclizative
atmospheric CO2 fixation methods by allyl amines leading to
cyclic carbamates, which constitute an important class of
heterocyclic compounds serving as synthetic intermediates
for complex molecules9 or as biologically active agents,10 has
been reported.11 Both reactions require the concomitant use
of stoichiometric amounts of I2 and an external strong base
(TMG11a or Cs2CO311b), which would trap the liberated
strong acid (HI), to gain high yields of product. As related
reactions, metal-catalyzed cyclizative CO2 fixations by pro-
pargyl amines under pressurized conditions or supercritical
CO2 have also been developed.12 With these backgrounds in
mind, we envisaged that an efficient cyclizative atmospheric
fixation of CO2 by allyl amines utilizing t-BuOI under mild
conditions would be feasible without the use of external
strong bases or metal catalysts (Scheme 1).
Table 1. Substrate Scope of Allyl Aminesa
Scheme 1. Cyclizative CO2 Fixation under Neutral Conditions
To verify the hypothesis, we treated the simplest allyl
amine (1a) with an equimolar amount of t-BuOI, which
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Pampaloni, G. Chem. Rev. 2003, 103, 3857. (b) Werner, E. A. J. Chem.
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Chem. 2006, 14, 4227. (c) Barbachyn, M. R.; Ford, C. W. Angew. Chem.,
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A. M.; Forbes, M. J. Med. Chem. 1989, 32, 1673.
a Reaction conditions: CO2 (1 atm), allyl amine (0.5 mmol), NaI
(0.5 mmol), t-BuOCl (0.5 mmol), and MeCN (3 mL). b Isolated yield.
c Reaction was conducted at 0 °C. d CH2Cl2 was used as a solvent.
ꢀ
~
(11) (a) Egido, G. E; Fernandez, I.; Munoz, L. Synth. Commun. 2006,
36, 3029. (b) Toda, T.; Kitagawa, Y. Angew. Chem., Int. Ed. Engl. 1987,
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Org. Lett., Vol. 14, No. 18, 2012
4875

gave very poor yields. The reason why t-BuOI is the most
suitable iodinating reagent in the reaction system could be
due to the liberation of only a weak acid (t-BuOH) instead
of HI that should be trapped by an external base in similar
reaction systems.9
Table 2. Substrate Scope of Homoallyl and Propargyl Aminesa
Having optimized the reaction conditions, the substrate
scope was then explored (Table 1). β-Branched allyl amine
1b was transformed into the corresponding carbamate
2b in moderate yield (entry 2). An allyl amine having a
γ-disubstituent 1c was also applicable to the reaction (entry 3).
When structurally defined geometric isomers 1d and 1e
were employed as substrates, the reaction proceeded ster-
ospecifically to afford 2d and 2e as single stereoisomers in
bothcases (entries 4 and 5).14 Moreover, N,N-diallylamine
(1f) was successfully transformed into the corresponding
carbamate 2f while keeping the other allylic moiety intact
(entry 6). N-Substitution with alkyl groups did not signifi-
cantly retard reaction efficiencies (entries 7ꢀ9). Various
functionalities showed good compatibility with the reaction
conditions, leading to the corresponding cyclic carbamates
2jꢀ2l in good to high yields (entries 10ꢀ12).
The successful results in the transformation of allyl
amines into five-membered cyclic carbamates through
the CO2 fixation prompted us to further investigate the
use of homoallyl and propargyl amines as substrates
(Table 2). When homoallyl amine 1m was subjected to
the reaction conditions, six-membered carbamate 2m was
obtained in moderate yield (entry 1), while γ-branched
homoallyl amine 1n was also converted to the correspond-
ing carbamate 2n in moderate yield (entry 2). Unfortu-
nately, the reaction using the simplestpropargylamine (1o)
failed to provide the desired product 2o (entry 3). In sharp
contrast, amines bearing a gem-disubstituent at the pro-
pargylic position gave cyclic carbamates 2p and 2q in good
yields as sole constitutional isomers with an E-configuration
(entries 4 and 5).14 This significant discrepancy in these
reaction outcomes would be explained in terms of the
“ThorpeꢀIngold effect”15 through the intramolecular cy-
clization process from the intermediately generated iodo-
nium intermediates (vide infra). It is noted that the silyl
group on the acetylenic carbon of 1r survived the reaction
conditions in which “Iþ” species coexist, leading to 2r
having a tetra-substituted olefinic moietyin moderate yield
(entry 6).
a Reaction conditions: CO2 (1 atm), homoallyl or propargyl amine
(0.5 mmol), NaI (0.5 mmol), t-BuOCl (0.5 mmol), and MeCN (3 mL).
b Isolated yield.
was generated in situ from NaI and t-BuOCl,6,7 under
the atmospheric pressure (1 atm) of CO2 in acetonitrile
at room temperature. Gratifyingly, the expected 4-
iodomethyl-2-oxazolidinone (2a) was successfully produced
and isolated in 47% yield. To improve the efficiency of
the reaction, reaction parameters such as solvents and
temperatures were scrutinized (Table S1). As a result, the
reaction at a lower temperature (ꢀ20 °C) in acetonitrile
was found to give the desired carbamate 2a in the highest
yield of 91% (entry 1, Table 1). The reactions with other
iodinating reagents such as IPy2BF4 (BPIT) and N-
iodosuccinimide (NIS) resulted in rather low yields of 2a.13
TheemploymentofI2 alone or the concomitant use of I2/Et3N
The oxazolidinones that were obtained by our method
would serve as useful building blocks, because an iodo-
functionality attached to sp3- or sp2-hybridized carbon
(14) The determination of their stereochemistry is described in the
Supporting Information.
(15) Beesley, R. M.; Ingold, C. K.; Thorpe, J. F. J. Chem. Soc., Trans.
1915, 107, 1080.
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Renhowe, P. A.; Li, B. J. Am. Chem. Soc. 1999, 121, 7509. (g) Duddu, R.;
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(13) For details, see the Supporting Information.
4876
Org. Lett., Vol. 14, No. 18, 2012

Scheme 2. Facile Synthesis of AMOZ Starting from 1a
Scheme 3. Pausible Reaction Mechanism
cyclic carbamate 2a in the solution was identified upon
successive addition of t-BuOI to the solution.22 Based on
the experimental results, the most likely reaction mechan-
ism is illustrated in Scheme 3: (1) allyl carbamic acid A is
generated as a result of the product-favored equilibrium of
allyl amine and CO2;8 (2) the resulting carbamic acid A
reacts with t-BuOI to undergo protonꢀiodine exchange,
leading to an O-iodinated species B; (3) the intermediate B
would serve as an iodonium source to form cyclic iodo-
nium intermediate C; (4) intramolecular cyclization from
C would give a cyclic carbamate product, with the process
being possibly supported by the stereospecific production
of 2d and 2e.
atoms can be transformed into other functional groups.16
To demonstrate a synthetic application of the present
reaction, a three-step preparation of 3-amino-5-morpholi-
nomethyl-2-oxazolidinone (AMOZ),17 which is a synthetic
intermediate of moxnidazole (antiparasite drug)18 and
furaltadone (antibacterial drug),18a,19 was efficiently ac-
complished starting from allyl amine 1a (Scheme 2). The
CO2 fixation by 1a was applicable to a gram scale opera-
tion, producing 2a in 88% yield. The iodo functionality
of 2a was then substituted with a morpholino group, lead-
ing to oxazolidinone 3 in good yield. The treatment of 3
with O-(diphenylphosphinyl)hydroxylamine (DppONH2)20
and NaH in DMF afforded AMOZ in 70% yield. The fact
that the conventional synthetic route to AMOZ requires as
many as six steps starting from (2,2-dimethyl-1,3-dioxolan-4-
yl)methanol as a starting material21 demonstrates the utility
of our reaction.
In conclusion, we have developed an efficient, metal/
base-free, and nonpressurized CO2 fixation by allyl amines,
leading to cyclic carbamates utilizing t-BuOI. The method
was applicable to a wide range of unsaturated amines under
mild conditions.
For a deeper understanding of the reaction mechanism,
several experiments were conducted. In situ monitoring of
a CD3CN solution of a mixture of allyl amine (1a) and
t-BuOI under a N2 atmosphere using the 1H NMR tech-
Acknowledgment. This work was supported by a
Grant-in-Aid for Scientific Research on Innovative Areas
“Molecular Activation Directed toward Straightforward
Synthesis” from the Ministry of Education, Culture,
Sports, Science, and Technology (MEXT), Japan. One of
the authors (Y.T.) acknowledges support from the Fron-
tier Research Base for Global Young Researchers, Osaka
University, on the Program of MEXT.
1
nique revealed that no change in the H NMR spectrum
of allyl amine occurred. On the other hand, under a
CO2 atmosphere similar monitoring (1H, 13C NMR,
and FT-IR) of a CD3CN solution of 1a without t-BuOI
indicated quantitative formation of allylammonium
allylcarbamate.8,13 Furthermore, gradual formation of
Supporting Information Available. General procedures,
spectral data for new compounds, and NMR experiments
results. This material is available free of charge via the
Internet of http://pubs.acs.org.
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unknown structure was also observed, which was too unstable to be
isolated.
~
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M. I. N.; Ramos, F. J. Agric. Food Chem. 2011, 59, 11927.
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The authors declare no competing financial interest.The authors
declare no competing financial interest.
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