A combined computational and experimental investigation of the oxidative ring-opening of cyclic ethers by oxoammonium cations

Article abstract of DOI:10.1039/c6ob00347h

The propensity of oxoammonium cations to facilitate the oxidative ring-opening of cyclic ethers to their corresponding distal hydroxy ketones is investigated. The reaction has been evaluated using experimental and computational methods to gain deeper insight into trends in reactivity.

Full text of DOI:10.1039/c6ob00347h

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Journal Name
RSCPublishing
ARTICLE
A Combined Computational and Experimental
Investigation of the Oxidative Ring-Opening of Cyclic
Ethers by Oxoammonium Cations
Cite this: DOI: 10.1039/x0xx00000x
Jacob. J. Loman,a Emma R. Carnaghan,a Trevor A. Hamlin,a John M. Ovian,a
Christopher B. Kelly,a Michael A. Mercadante,a and Nicholas E. Leadbeatera,b*
Received 00th January 2012,
Accepted 00th January 2012
DOI: 10.1039/x0xx00000x
The propensity of oxoammonium cations to facilitate the oxidative ringꢀopening of cyclic
ethers to their corresponding distal hydroxy ketones is investigated. The reaction has been
evaluated using experimental and computational methods to gain deeper insight into trends in
reactivity.
www.rsc.org/
Introduction
Oxoammonium salts are versatile oxidants that enable a wide
range of oxidation reactions to be performed under mild
conditions.1 These salts are metal free and recyclable and hence
serve as greener alternatives to traditional metalꢀbased oxidants.
While much of the literature involving oxoammonium salts
centres around the conversion of alcohols to their
corresponding carbonyl species,2 their ability to facilitate nonꢀ
traditional oxidation reactions is of particular interest. In our
laboratory, we have employed 4ꢀNHAcꢀTEMPO+ BF4
ꢀ
(Bobbitt’s salt,
1) extensively in the context of this
underexplored platform.3 Specifically, our interests lie in the
capture a transient oxidised intermediate with a nucleophilic
species, resulting in a net oxidative functionalisation.3c,4,5 Such
a strategy has also been employed successfully by Garciaꢀ
Mancheño6 and Bailey.7 Representative examples of this
concept are the cleavage of benzyl and allyl ethers via treatment
1
(Figure 1aꢀb).4,8 These reactions have proved to be
Figure 1: Oxidative cleavage of ethers using oxoammonium salt
1
with
valuable as mild deprotection strategies for alcohols. We have
also probed the mechanism of these and other oxidative
processes involving
1 computationally using density functional
Results and Discussion
theory (DFT) and correlated the results with experimentallyꢀ
derived trends in reactivity.8
We began our study by examining the first step of the reaction
computationally, namely the hydride abstraction from various
Based on the previous study with allyl and benzyl ethers,
we envisioned cyclic ethers, for example epoxides, oxetanes,
tetrahydrofurans (THFs), and tetrahydropyrans (THPs), could
be oxidatively ringꢀopened to allow efficient access to hydroxy
ketones (Figure 1c). Specifically, these ethers would need to
possess an αꢀaryl substituent because of the mechanistic nature
of oxoammonium cationꢀmediated oxidation. Despite their
common place nature in organic chemistry, there are
surprisingly few examples of this class of transformation in the
literature. Most reports centre on oxidative opening of the
smaller strained rings, namely oxetanes and epoxides.9,10,11,12,13
However, no mild method yet exists for this process, to the best
cyclic ether substrates by
1 to give the corresponding oxonium
ion (Figure 2). The highest energy barrier was found for styrene
oxide (n
= 1) with a ꢁG‡ leading to the intermediate of 26.4
kcal molꢀ1. This is likely a consequence of the large requisite
strain imparted during oxygenꢀmediated cation stabilization.
This is similarly reflected in the ꢁ
intermediate Interestingly, it appears that strain is not the only
factor governing the activation barrier of this process (i.e. the
for the activation barrier of a THP is greater than that of an
G value of the oxonium
.
ꢁG
oxetane). This may stem from differences in steric repulsion
between the -gem diꢀmethyl groups of the oxoammonium
cation and the ethereal substrate. Despite these differences, the
of our knowledge. Hence, using 1, we assessed the viability of
such a process, employing combined computational and
experimental techniques. We report out results here.
ꢁ
G values to the intermediate oxonium ion for oxetanes, THFs
and THPs suggest that the process is favourable and
spontaneous, with energies ≥10 kcal molꢀ1 lower than the
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DOI: 10.1039J/Co6uOrnB0a0l3N4a7Hme
oxonium ion derived from styrene oxide. In light of this, we
envisioned that oxetane, THF and THP scaffolds would likely
undergo oxidative ringꢀopening whereas epoxides would at the
very least be recalcitrant to cleavage.
Table 1 Optimisation of reaction conditions for the oxidative cleavage of
cyclic ethers a
O
O
1
OH
solvent, additive
concentration
3a
2a
Entry
1
Solvent
Conc. (M)
0.2
1 (eq.)
Additive
ꢀ
Yield
48% c
MeCN:H2O
(7:3)
1.02
MeCN:H2O
(8:2)
MeCN:H2O
(8:2)
MeCN:H2O
(8:2)
MeCN:H2O
(8:2)
MeCN:H2O
(8:2)
MeCN:H2O
(8:2)
MeCN:H2O
(8:2)
MeCN:H2O
(8:2)
2
3
0.2
0.4
0.2
0.2
0.4
0.4
0.5
0.4
0.4
0.4
0.4
1.02
1.02
1.12
2.00
1.12
2.00
1.02
1.12
2.24
2.24
1.12
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
57% c
39%d
67%d
61% d
75% c
51% d
ꢀ
4
5
6
7
8
9d
10
11
12e
ꢀ
MeCN:H2O
(1:1)
MeCN:H2O
(1:1)
MeCN:H2O
(8:2)
NaHCO3
(2 eq.)
2,6ꢀlutidine
(2 eq.)
ꢀ
Figure 2: Computed reaction profile for the hydride abstraction from
cyclic ethers by 1 based on the envisioned reaction pathway
ꢀ
ꢀ
63%c
With these data in hand, the oxidative ring opening process
was explored experimentally. We chose 2ꢀphenyloxetane, 2a
as a model substrate. Utilizing a slight excess of in a dilute
mixture of acetonitrile and water (7:3) at room temperature, we
obtained a 48% yield of the desired ringꢀopened ꢀhydroxy
ketone 3a, along with some polymeric sideꢀproducts (Table 1,
Entry 1). Adjusting the acetonitrile/water ratio to 8:2 did give
some improvement in yield (Entry 2), as did increasing the
,
a Performed on a 1.0 mmol scale unless otherwise noted, solvent ratios by
volume, conducted at room temperature with progress monitored by 1HꢀNMR
for consumption of starting material (~ 12 h on average). b Yield determined
by 1HꢀNMR using an internal standard c Isolated yield. d Reaction performed
at 50 °C. e Performed on a 10.0 mmol scale.
1
β
With optimised conditions in hand, our next objective was
to prepare a range of substrates for reaction screening. We
chose to define a modular synthetic route that could be used for
oxetane, THF, and THP substrates alike (Scheme 2). Friedelꢀ
Crafts acylation followed by sodium borohydride reduction and
loading of
1 from 1.02 to 1.12 equivalents (Entry 4). Increasing
the concentration from 0.2 M to 0.4 M improved the yield
further (Entry 6). Unfortunately, increasing the concentration or
quantity of
1 further had a deleterious effect on the reaction,
potassium t
ꢀbutoxide mediated15 ring closure proved to be a
giving a complex mixture of unidentifiable polymeric products
1
by H NMR in addition to the desired βꢀhydroxy ketone (Entry
facile method to generate the desired cyclic ether precursors
(Table 2).
7). Even at dilute concentrations, elevated temperatures had a
similar effect to increasing concentration, leading primarily to
polymerisation (Entry 9). Conditions similar to those used by us
and others for the baseꢀmediated oxidation of alcohols were
also evaluated.2c,14 However, these too proved unsuccessful
(Entries 10 & 11). Returning to our original conditions, we
scaled up the reaction and found that although the product yield
decreased somewhat, we were able to obtain pure 3a in 63%
isolated yield (Entry 8). We decided to take these conditions on
to our substrate screening.
O
O
Cl
Cl
Cl
n
n
AlCl3, CH2Cl2
R
R
NaBH4
MeOH
OH
O
t-BuOK
THF
Cl
n
n
To augment our reaction optimization studies, we also
tested various nucleophiles in search of alternative addition
products. One issue with using nucleophiles in conjunction with
the oxoammonium salt is the requirement that they not be too
basic nor easily oxidised in order to avoid competitive reactions
with the salt itself and hence oxidant consumption. Sodium
cyanide, sodium iodide, sodium azide, sodium acetate, and
lithium chloride were all examined and in all cases, no
nucleophilic addition products were observed.
R
R
Scheme 1: Preparation of cyclic ether substrates
2 | J. Name., 2012, 00, 1-3
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Table 2 Preparation of cyclic ethers a
although the activation energy for the first step is lower than the
energy required to continue on from the cationic oxetane
intermediate, it is more favourable than the reverse reaction.
Beyond this second transition state, the rest of the energetics
are calculated to be very favourable towards our desired
product.
Entry
1
Cyclic Ether
Yield (%)b
77
O
Interestingly, the energetics for the epoxide substrate
(Figure 3A) suggests that if we were able to overcome the
energy barrier for the hydride transfer step, the second step of
the reaction would be highly favoured and proceed rapidly.
However, the barrier for the initial hydride transfer would still
likely prevent the reaction from proceeding favourably.
2
3
77
90
2b
F
Table 3 Scope of the methodology for oxidative cleavage of cyclic ethers a
4
92
5
6
92
67
Entry
1
Cyclic Ether
Product
Yield (%)b
61
O
7
8
91
92
2
3
56
ꢀ
2b
F
9
92
99
4
ꢀ
10
5
6
45
23
a Prepared using the approach shown in Scheme 2. b Isolated yield.
These cyclic ethers were then subjected to our optimised
conditions (Table 3). While it was possible to affect the ringꢀ
opening of 2a and 2b, other oxetane substrates resulted in
inseparable mixtures of products or complete polymerisation
(Table 3, Entries 1ꢀ4). Likewise, only certain THF substrates
could be opened or adequately purified in moderate yield
(Entries 5ꢀ9). Using our reaction conditions, we observed
substantial polymerization when using 2ꢀphenyltetrahydropyran
7
8
36
ꢀ
(
2j), rather than the desired δꢀhydroxy ketone (Entry 10). Not
surprisingly, attempts using styrene oxide failed to afford any
of the αꢀhydroxy ketone (not shown).
9
ꢀ
ꢀ
Surprised by the rather limited scope of this reaction, we
attempted to rationalize our results computationally. The
complete reaction profiles (Figure 3) were able to provide at
least some explanation for the difficulties encountered during
our experimental studies. The interplay between the stability of
resulting cationic intermediate following hydride abstraction
and the activation barrier for ring opening may explain the
polymerisation and sideꢀproduct mixtures we observed
experimentally. In all cases, the energy required to continue
towards the second transition state is greater than the energy
needed to abstract the hydride in the first step. In the case of the
THF and THP (Figure 3C & D), the activation barrier for the
ring opening event is even greater than the hydride transfer
itself. Thus the first cationic intermediate may become trapped
in a potential energy well, extending the lifetime of this ion.
Other nonꢀproductive reaction pathways may then emerge. In
the case of the oxetane reaction (Figure 3B), we saw that
10
a Conditions: cyclic ether (10.0 mmol, 1 equiv), 1 (11.2 mmol, 1.12 equiv),
8:2 vol/vol MeCN:H2O (25 mL, 0.4 M in the cyclic ether). b Isolated yield.
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Figure 3: Computed reaction profiles for the ringꢀopening reactions of styrene oxide, 2a, 2e, and 2j at B3LYP/6ꢀ31+g(d). Free energies relative to
the reactants in the gas phase in units of kcal molꢀ1.
time, the crude reaction solution was diluted with Et2O (200
mL) and deionized water (200 mL). The phases were separated
and the aqueous layer was extracted with Et2O (3 × 50 mL).
The combined organic layers were washed with 2M HCl (≈ 100
mL), deionized water (≈ 100 mL), brine (≈ 100 mL), and dried
with Na2SO4. The solvent was removed in vacuo by rotary
evaporation to give the an orange oil which was then adhered to
silica gel using 1.5 weight equivalents of SiO2 (relative to the
theoretical yield) suspended in DCM. The dryꢀpacked material
was gently added atop a silica gel plug. The plug was washed
with a 9:1 by volume mixture of Hex:EtOAc (3 column
volumes) followed by an 8:2 mixture of Hex:EtOAc (1.5
column volumes). The desired product was eluted off the plug
via a 6:4 by volume mixture of Hex:EtOAc (2ꢀ3 column
volumes). The solvent was removed in vacuo by rotary
evaporation affording the pure 3a (0.92 g, 61%) as a clear
yellow oil. 1H NMR (CDCl3, 400 MHz) δ ppm 2.67 (br. s., 1 H)
Conclusions
In summary, we present
computational study of the oxidative ringꢀopening of cyclic
ethers facilitated by . The computations performed on this
a
combined synthetic and
1
transformation aid in the understanding of the limitations of the
methodology. Full elucidation of the reaction pathway via DFT
calculations revealed that the cationic species formed after
hydride transfer was comparably stable. The calculated energy
“valley” indicated to us that the reactive cationic intermediate is
relatively longꢀlived, enabling it to undergo undesired side
reactions such as the polymerization observed. This correlated
well with our observed experimental results.
Experimental section
Representative Procedure for Oxidative Ring-Opening:
Synthesis of 3-hydroxy-1-phenyl-1-propanone (3a)
3.24 (t, J=5.33 Hz, 2 H) 4.04 (t, J=5.30 Hz, 2 H) 7.45 ꢀ 7.52 (m,
2 H) 7.56 ꢀ 7.63 (m, 1 H) 7.95 ꢀ 8.00 (m, 2 H). 13C NMR
(CDCl3, 100 MHz) δ ppm 41.0 (CH2), 58.2 (CH2), 128.4 (CH),
128.9 (CH), 133.7 (CH), 137.1 (C), 200.5 (C).
To a 50ꢀmL round bottom flask equipped with stir bar was
added the oxoammonium salt
1 (3.36 g, 0.0112 mol, 1.12
equiv.) and a 8:2 by volume mixture of MeCN:H2O (25 mL, 0.4
M in the oxetane). The salt was allowed to dissolve to give a
homogeneous solution. After this time, the 2ꢀphenyloxetane
(1.34 g, 0.01 mol, 1.0 equiv.) was added slowly to the stirred
solution. The reaction was allowed to stir overnight. After this
Computational Studies
Quantum chemical calculations were performed using Gaussian
09.16 All optimized geometries were calculated using B3LYP, a
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hybrid density functional, with the 6ꢀ31G(d) basis set,17,18,19
with structures at energy minima showing no imaginary
frequencies and transitionꢀstate structures showing one
imaginary frequency. These calculations were conducted in the
gas phase, but the trends found can be expected to remain
consistent in solution.20 The calculated trends are further
supported by our experimental results. Conformational space
was thoroughly explored and the proposed structures are
expected to be global energy minima on the potential energy
surface. The Gibbs free energies were calculated by the sum of
electronic and thermal free energy. The thermal free energy
thermodynamic correction factor was obtained via frequency
analysis. All calculations were carried out at standard
conditions: 298 K and 1 atm. All energy values shown are in
kcal molꢀ1, bond lengths are reported in Ångstroms (Å), and
bond angles in degrees (˚). Molecular figures were generated
using CYLView.21
8141; (
b
) T. A. Hamlin, C. B. Kelly and N. E. Leadbeater, Eur. J.
Org. Chem., 2013, 3658ꢀ3661. (c) C. B. Kelly, M. A. Mercadante, R.
J. Wiles and N. E. Leadbeater, Org. Lett., 2013, 15, 2222ꢀ2225.
C. B. Kelly, J. M. Ovian, R. M. Cywar, T. R. Gosselin, R. J. Wiles
and N. E. Leadbeater, Org. Biomol. Chem., 2015, 13, 4255ꢀ4259.
C. B. Kelly, K. M. Lambert, M. A. Mercadante, J. M. Ovian, W. F.
Bailey and N. E. Leadbeater, Angew. Chem., Int. Ed., 2015, 54, 4241ꢀ
4245.
4
5
Acknowledgements
This work was supported by the National Science Foundation
CAREER Award CHEꢀ0847262) and the University of
Connecticut Office of Undergraduate Research.
6
7
8
9
H. Richter and O. García Mancheño, Eur. J. Org. Chem., 2010, 4460ꢀ
4467.
Notes and references
P. P. Pradhan, J. M. Bobbitt and W. F. Bailey, J. Org. Chem., 2009,
74, 9524–9527.
a
Department of Chemistry, University of Connecticut, 55 North
T. A. Hamlin, C. B. Kelly, J. M. Ovian, R. J. Wiles, L. J. Tilley and
N. E. Leadbeater, J. Org. Chem., 2015, 80, 8150ꢀ8167.
Eagleville Road, Storrs, CT 06269, United States. Eꢀmail:
nicholas.leadbeater@uconn.edu
b
K. Surendra, N. S. Krishnaveni and K. R. Rao, Tetrahedron Lett.
2005, 46, 4111ꢀ4113.
,
,
,
Department of Community Medicine & Health Care, University of
Connecticut Health Center, The Exchange, 263 Farmington Ave,
Farmington, CT 06030, United States.
10 V. Nair, R. Rajan, K. Mohanan and V. Sheeba, Tetrahedron Lett.
2003, 44, 4585ꢀ4588.
† Electronic supplementary information (ESI) available: Experimental
11 (a) V. Le Boisselier, E. Dunach and M. Postel, J. Organomet. Chem.
and
computational
details,
characterization
of
substrate
precursors/substrates/products, and copies of H and 13C, NMR spectra.
1
1994, 482, 119ꢀ123. (b) C. Coin, T. Zevaco, E. Dunach and M.
Postel, Bull. Soc. Chim. Fr., 1996, 133, 913ꢀ918.
See DOI: 10.1039/b000000x/
12 T. A. G. Duarte, A. C. Estrada, M. M. Q. Simões, I. C. M. S. Santos,
A. M. V. Cavaleiro, M. G. P. M. S. Neves and J. A. S. Cavaleiro,
Catal. Sci. Technol., 2015, 5, 351ꢀ363.
13 R. F. Moreira, E. Y. Tshuva and S. J. Lippard, Inorg. Chem., 2004,
43, 4427ꢀ4434.
14 J. M. Bobbitt, A. L. Bartelson, W. F. Bailey, T. A. Hamlin and C. B.
Kelly, J. Org. Chem., 2014, 79, 1055ꢀ1067.
15 F. Bertolini, S. Crotti, V. Di Bussolo, F. Macchia, and M. Pineschi, J.
Org. Chem., 2008, 73, 8998ꢀ9007.
16 Gaussian 09, Revision A.02, M. J. Frisch, G. W. Trucks, H. B.
Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, G. Scalmani,
V. Barone, B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato,
X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng, J. L.
Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa,
M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, J.
A. Montgomery, Jr., J. E. Peralta, F. Ogliaro, M. Bearpark, J. J.
Heyd, E. Brothers, K. N. Kudin, V. N. Staroverov, R. Kobayashi, J.
Normand, K. Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar, J.
Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene, J. E. Knox, J. B.
Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E.
Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W.
Ochterski, R. L. Martin, K. Morokuma, V. G. Zakrzewski, G. A.
Voth, P. Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels, Ö.
1
For reviews on TEMPOꢀbased oxoammonium salts and some of their
reactions, see: ( ) N. E. Leadbeater and J. M. Bobbitt, Aldrichimica
Acta, 2014, 47, 65ꢀ74. (
Synth., 2005, 82, 80ꢀ86; (
a
b
) J. M. Bobbitt and N. Merbouh, Org.
c
) H. Richter, R. Fröhlich, C.ꢀG. Daniliuc
and O. García Mancheño, Angew. Chem., Int. Ed., 2012, 51, 8656ꢀ
8660; ( ) R. Rohlmann, T. Stopka, H. Richter and O. Garcıa
d
́
Mancheño, J. Org. Chem., 2013, 78, 6050ꢀ6064..
2
3
M. A. Mercadante, C. B. Kelly, J. M. Bobbitt, L. J. Tilley and N. E.
Leadbeater Nat. Protoc., 2013, 8, 666ꢀ676.
For examples, see: (a) C. B. Kelly, M. A. Mercadante, T. A. Hamlin,
M. H. Fletcher and N. E. Leadbeater, J. Org. Chem., 2012, 77, 8131ꢀ
This journal is © The Royal Society of Chemistry 2012
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Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski and D. J. Fox,
Gaussian, Inc., Wallingford CT, 2009.
17 (
a
b
) V. Baron and M. Cossi, J. Phys, Chem. A., 1998, 102, 1995ꢀ2001;
(
) V. Barone, M. Cossi and J. Tomasi, J. Comp. Chem., 1998, 19
,
404ꢀ417.
18 ( ) A. D. Becke, J. Chem. Phys., 1993, 98, 5648ꢀ5652; (
a
b
) C. Lee, W.
Yang and R. G. Parr, Phys. Rev. B, 1988, 37, 785ꢀ789; (
Vosko, L. Wilk and M. Nusair, Can. J. Phys., 1980, 58, 1200ꢀ1211;
) P.J. Stephens, F. J. Devlin, C. F. Chabalowski and M. J. Frisch, J.
Phys. Chem., 1994, 98, 11623ꢀ11627.
19 ( ) R. Ditchfield, W. J. Hehre and J. A. Pople, J. Chem. Phys., 1971,
54, 724ꢀ728; ( ) W. J. Hehre, R. Ditchfield and J. A. Pople, J. Chem.
Phys., 1972, 56, 2257ꢀ2261; ( ) P. C. Hariharan and J. A. Pople,
c) S. H.
(d
a
b
c
Theor. Chim. Acta, 1973, 28, 213ꢀ222.
20 K. M. Lambert, J. M. Bobbitt, S. A. Eldirany, K. B. Wiberg and W. F.
Bailey, Org. Lett., 2014, 16, 6484ꢀ6487.
21 C. Y. Legault, CYLview, 1.0b. Université de Sherbrooke; 2009.
http://www.cylview.org.
6 | J. Name., 2012, 00, 1-3
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TOC GRAPHIC
TOC TEXT
The oxidative ring-opening of cyclic ethers using oxoammonium cations is investigated using
experimental and computational methods.