Aluminum-Catalyzed Formation of Functional 1,3,2-Dioxathiolane 2-Oxides from Sulfur Dioxide: An Easy Entry towards N-Substituted Aziridines

Article abstract of DOI:10.1002/adsc.201600831

Aluminum(III) complexes derived from aminotriphenolate ligands are shown to be excellent catalysts for the formation of cyclic sulfites from a range of (functionalized) terminal and internal epoxides, and ex situ generated sulfur dioxide. The developed catalytic protocol is characterized by its operational simplicity, wide scope in epoxide reaction partners, good to excellent isolated yields and mild reaction conditions [50–70 °C, p(SO₂) <1 bar]. The synthetic potential of these cyclic sulfites in organic synthesis is demonstrated in the preparation of N-substituted aziridines through a three-step protocol. (Figure presented.).

Full text of DOI:10.1002/adsc.201600831

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DOI: 10.1002/adsc.201600831
Aluminum-Catalyzed Formation of Functional 1,3,2-Dioxathio-
lane 2-Oxides from Sulfur Dioxide: An Easy Entry towards N-
Substituted Aziridines
Victor Laserna,a Eddy Martin,a Eduardo C. Escudero-Adꢀn,a
and Arjan W. Kleija,b,*
a
Institute of Chemical Research of Catalonia (ICIQ), the Barcelona Institute of Science & Technology, Av. Paꢁsos Catalans
16, 43007 Tarragona, Spain
Fax : (+34)-97-792-0823; Phone: (+34)-97-792-0247; e-mail: akleij@iciq.es
Catalan Institute of Research and Advanced Studies (ICREA), Pg. Lluꢂs Companys 23, 08010 Barcelona, Spain
b
Received: July 28, 2016; Revised: September 9, 2016; Published online: && &&, 0000
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201600831.
Abstract: Aluminum(III) complexes derived from reaction conditions [50–708C, p(SO2) <1 bar]. The
aminotriphenolate ligands are shown to be excellent synthetic potential of these cyclic sulfites in organic
catalysts for the formation of cyclic sulfites from synthesis is demonstrated in the preparation of N-
a range of (functionalized) terminal and internal ep- substituted aziridines through a three-step protocol.
oxides, and ex situ generated sulfur dioxide. The de-
veloped catalytic protocol is characterized by its op-
erational simplicity, wide scope in epoxide reaction Keywords: aluminum; aziridines; cyclic sulfites; ho-
partners, good to excellent isolated yields and mild mogeneous catalysis; sulfur dioxide
Introduction
a more general and sustainable route towards these
cyclic sulfites. In particular, low-temperature conver-
Small molecule catalysis and recycling has become sions and further widening the scope in reaction part-
a popular and rewarding theme in the field of organic ners may be required to promote these cyclic sulfites
synthesis.[1] In particular, the conversion of heterocu- as chemical building blocks. To this end, isolation of
mulenes such as carbon dioxide (CO2),[2] carbon disul- the pure sulfite targets is often hampered due to the
fide (CS2)[3] and isocyanates (R–NCO)[4] has received
a great deal of attention by enabling the synthesis of
various heterocyclic structures. Whereas the use of
CO2 as a carbon synthon in synthesis has now become
well established,[5] the use of sulfur dioxide (SO2) as
a reagent is still in its infancy.[6] One of the targeted
structures that can be prepared from SO2 are cyclic
sulfites (i.e., 1,3,2-dioxathiolane 2-oxides) by coupling
with epoxides (Scheme 1), providing structures of use
in polymer science, as electrolyte solvents or as syn-
thetic intermediates.[7]
The SO2 approach has been developed as a more
sustainable methodology compared to the convention-
al preparation of these scaffolds through a base-assist-
ed reaction of 1,2-diols with thionyl chloride that gen-
erates stoichiometric amounts of halide-containing
by-products.[8] Despite the development of various ef-
fective homogeneous and heterogeneous catalyst sys-
tems for the coupling of epoxides and SO2,[9] there
Scheme 1. Conversion of SO2 into cyclic sulfites by reaction
are still synthetic challenges to overcome pertinent to with epoxides: below the current approach.
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Table 1. Screening study towards the formation of the cyclic
sulfite product derived from 1,2-epoxyhexane and
DABSO using various catalysts and solvents.[a]
presence of mixtures of poly- and cyclic sulfites.
Moreover, as far as we know only limited potential
towards the more challenging coupling of internal ep-
oxides and SO2 has been reported to date. Conse-
quently, this restricts the synthesis of cyclic sulfites
mostly to the use of terminal oxiranes.
1
In recent years, we have reported on the applica-
tion of highly reactive and versatile aluminum(III)
aminotriphenolate catalysts (Scheme 1) in the activa-
tion of terminal and internal epoxides towards the
formation of various heterocyclic products[10] and
polymers.[11] Inspired by these results we envisaged
that these Al(III) complexes would also be potentially
useful for the coupling of epoxides and SO2 to afford
cyclic sulfites, and moreover could offer a more pow-
erful methodology towards their formation. The pres-
ent contribution will show that these catalyst systems
indeed show unparalleled reactivity and unusual
scope in the formation of these sulfur-containing het-
erocycles in good to excellent isolated yields under at-
tractively mild conditions. Furthermore, the use of
these cyclic sulfites as molecular synthons is demon-
strated in the preparation of N-substituted aziridines,
which can be easily obtained through oxidation of the
sulfite to a sulfate intermediate followed by subse-
quent aminolysis and a Wenker type base-assisted
cyclization.[12]
Entry
Catalyst
Solvent
t [h]
Yield [%][b]
1
2
3
4
5
6
7
8
A
B
C
D
E
F
G
H
C
C
C
C
–
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
EtOAc
THF
3
3
3
3
3
3
3
3
6
6
6
6
3
41
51
55 (63)[c]
45 (49)[c]
31
26
30
47 (58)[c]
9
59
23
24
19
45
10
11
12
13
DMF
MEK
CH3CN
Results and Discussion
[a]
General conditions: 3.0 mmol of 1,2-epoxyhexane,
2.5 mol% cat., 5.0 mol% NBu4I, solvent as indicated
(1 mL), 508C, 1 equiv. DABSO.
Isolated yield.
Isolated yield after a 6 h reaction time.
Our first attempts to produce cyclic sulfites from ep-
oxides and SO2 were based on the use of DABSO
(the bis-SO2 adduct derived from DABCO: 1,4-diaza-
bicyclo[2.2.2]octane) as an easy to handle SO2 surro-
gate,[13] see Table 1. Among the metal complexes used
(cf., A–G), the Al(III) aminotriphenolate C, com-
bined with an external nucleophile (NBu4I) to medi-
[b]
[c]
ate the epoxide ring-opening, gave the best results in the reaction when more SO2 (DABSO) is consumed.
terms of isolated yield (entry 3; 55% after 3 h, 63% Such diamines (and other N-donor Lewis bases) were
after 6 h). Other polar solvents beside acetonitrile found to be good ligands for Al(III) and Fe(III) ami-
were also examined but gave inferior results (en- notriphenolate complexes[15] and the presence of
tries 9–12). More importantly, the use of the nucleo- DABCO almost certainly causes catalyst deactivation.
philic additive only (entry 13) produced only a slightly In order to avoid in situ deactivation of Al complex
lower yield (45%) than noted for the best case scenar- C, we designed a different protocol that takes advant-
io (entry 3).[14] We therefore investigated the kinetic age of easy SO2 generation under practical conditions
profile for the synthesis of 1 from 1,2-epoxyhexane using a combination of copper powder and H2SO4. Ex
and DABSO in more detail (Figure 1).
situ formation of SO2 and using a gentle and opti-
As can be judged from Figure 1, formation of 1 in mized nitrogen flow (see the Supporting Information
the presence or absence of complex C [i.e., traces (a) for more details) to transport the SO2 to a reactor
and (b) in the graph] does not show much difference, containing the epoxide and catalyst should deliver
and the yield of cyclic sulfite 1 reaches a plateau after a more productive protocol for cyclic sulfite forma-
around 800 min. This suggests that the Lewis acid cat- tion. Indeed, when we probed such conditions
alytic potential of Al complex C is significantly ham- (Table 2 and Figure 1) we noted that the reaction to-
pered under these experimental conditions. The most wards the formation of 1 proceeded more smoothly
likely reason for this lethargic behaviour is the release and gave the product in nearly quantitative NMR
of the bicyclic amine DABCO during the course of yield after only 200 min.
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1
Figure 1. Kinetic profiles determined by H NMR (CD3CN) for the synthesis of 1 using DABSO (1.2 equiv.) and mesitylene
as internal standard. (a) Using C/NBu4I as binarycatalyst; (b) Only NBu4I; (c) Reaction performed with ex situ generated
SO2 from H2SO4/Cu: epoxide (3 mmol), C (1.0 mol%), NBu4I (2.5 mol%), CH3CN (1.0 mL), 508C.
Table 2. Optimization of the protocol involving ex situ SO2
(cf., formation of compounds 1–18, Figure 2) using
formation from Cu/H2SO4 using catalysts A–C/NBu4X and
CH3CN in the formation of the cyclic sulfite product 1.[a]
1.0 mol% of Al complex C, 2.5 mol% of NBu4I in
CH3CN at 508C. Under these conditions, cyclic sulfite
1 could be isolated in excellent yield (93%) as a mix-
ture of two diastereoisomers in an 82:18 ratio. The
presence of two diastereoisomers is the result of the
non-planarity of the cyclic sulfite, with the sulfur lone
pair either being on the same or opposite side of the
ring substituent. The two diastereoisomers are well
separated and assignable by NMR analysis (see the
Supporting Information). For instance, for 1 the
major isomer is characterized by three distinct signals
for the hydrogens attached to the sulfite ring whereas
the minor isomer shows only two peaks located at
4.52 and 4.32 ppm. The much larger difference in
chemical shift for the methylene H of the ring struc-
ture (Dd=0.76 ppm) in the major isomer seems to
suggest that this diastereoisomer has the sulfur lone
pair on the same face as the butyl substituent, thereby
causing an anisotropic shift for the axial H of the
methylene group. For the majority of the other cases
Entry Cat. [mol%] Nu [mol%]
T [8C] Yield [%][b]
1
2
3
4
5
6
7
8
–
–
–
–
NBu4I (1.0)
NBu4I (2.5)
NBu4I (5.0)
50
50
50
11
29
61
25
85
41
65
86
61
22
84
NBu4Br (2.5) 50
C (0.5)
B (0.5)
A (0.5)
C (1.0)
C (1.0)
C (0.5)
C (0.5)
NBu4I (2.5)
NBu4I (2.5)
NBu4I (2.5)
NBu4I (2.5)
NBu4I (1.0)
NBu4I (2.5)
NBu4I (2.5)
50
50
50
50
50
25
70
9
10
11
[a]
[b]
General conditions: 3.0 mmol of 1,2-epoxyhexane, C
(amount indicated), NBu4X (amount indicated), CH3CN
(1 mL), Cu (3 equiv.) in H2SO4 (10 mL) at 908C (ex situ),
2 h.
NMR yields based on mesitylene as an internal standard.
We then further optimized this improved protocol, studied similar drs were noted. Fortunately, the X-ray
and Table 2 summarizes the results from these experi- molecular structure of cyclic sulfite 13 could be deter-
ments. Clearly, catalyst C shows the best performance mined (Figure 3): the relative orientation of the ring
(entries 5–7) with markedly better yields of 1 com- substituent (p-biphenylene) and the sulfur lone pair is
pared to the reaction in the absence of the complex in line with the NMR observations for 1 and most of
(cf., entries 2 versus 5) using a lower amount of Al the other isolated products.[16]
complex C (0.5 mol%) and nucleophile (2.5 mol%).
Many different and potentially useful substituents
Higher amounts of Al complex (entry 8) and an ele- on the cyclic sulfite ring can be introduced including
vated temperature (708C, entry 11) did not much alcohol (4), allyloxo (6), propargyloxo (7), and tosyl
affect the yield of 1, suggesting that the conditions of ester (10) groups that do not seem to hamper product
entry 5 and 8 are fairly optimal.
formation through coordination to the Al center in
Next we investigated the scope of terminal epoxide C.[17] In those cases where styrene oxides were used
substrates in the formation of various cyclic sulfites (cf., the formation of 11–13), a higher loading of the
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Figure 3. X-ray molecular structure for 13. Selected bond
lengths (ꢄ) and angles (8): S(1A)–O(1)=1.454(7), S(1A)–
O(2 A)=1.633(6), S(1A)–O(3 A)=1.614(6); O(1A)–S(1A)–
O(2A)=105.3(4), O(1A)–S(1A)–O(3A)=108.9(4).
pound and isolated in good yield (89%). Compound
14 could be easily converted into the mixed sulfite/
carbamate 17 (52%) and sulfite/carbonate 18 (81%)
by treatment with phenyl carbamate and CO2, respec-
tively, under appropriate reaction conditiACTHNUTRGNEUNG
ons.[10a,f]
These latter conversions clearly demonstrate the post-
modification potential of functional sulfites.
Motivated by the successful preparation of func-
tional mono-substituted sulfites, we next turned our
focus towards the more challenging conversion of in-
ternal epoxides. We selected cyclohexene oxide
(CHO) as a representative epoxide and followed its
conversion in time using the optimized conditions es-
tablished for 1–18 (508C, 3 equiv. of SO2, 1.0 mol% of
C). However, NBu4Br was utilized instead as bromide
nucleophiles were previously shown to be more effec-
tive for internal epoxide conversion compared to
iodide-based ones.[10a,c,e] The conversion at 508C
1
proved to be a bit sluggish and, moreover, H NMR
analysis showed the presence of peaks reminiscent of
poly-sulfites with only trace amounts of cyclic prod-
uct. Therefore, the reaction between CHO and SO2
mediated by complex C/NBu4Br was then carried out
at 708C using longer reaction times, and to our de-
light we found that the reaction mixture contained
virtually only the cyclic sulfite product 19 (see the
Supporting Information for more details). The latter
was isolated in moderate yield (46%; Figure 4) by
chromatographic purification. Notably, compound 19
was mostly isolated as the trans isomer which is the
expected result if the cyclic sulfite would be formed
by back-biting of an initially formed poly-sulfite poly-
mer.[19]
Figure 2. Synthesis of cyclic sulfites 1–18 from various termi-
nal epoxides using ex situ generated SO2. Conditions (unless
stated otherwise): complex C (1.0 mol%), NBu4I (2.5 mol%),
CH3CN (1.0 mL), 508C, 3 h. Reported yields are isolated
ones after column purification.
Then other internal epoxides were examined as re-
action partners thereby producing the cyclic sulfites
20–29 generally in appreciable yields (except for 28;
21%). The more rigid nature of the 8-membered ring
epoxide leading to cyclic sulfite 29 delivers the prod-
nucleophile was required to prevent significant forma- uct in much better yield (64%) than noted for 28;
tion of ketone by-products through Meinwald rear- such a distinct behaviour was previously also noted in
rangement.[18] Interestingly, mono-sulfite 14 derived cyclic carbonate formation.[10e] The likely reason for
from its bis-epoxide precursor could be isolated in this is the unfavourable conformation upon activation
61% yield and incorporates a synthetically useful oxir- by the Al(III) center in complex C thereby complicat-
ane unit. By increasing the amount of SO2 to 6 equiv., ing nucleophile-assisted ring-opening. The introduc-
the bis-sulfite 15 was obtained as the major com- tion of a double bond in the 8-membered ring reduces
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of cyclic sulfites from SO2. For the conversion of
trans-2,3-dimethyloxirane (leading to 23) and its cis-
isomer (giving rise to 24) a different behaviour was
noted. Whereas the trans substrate retains the original
stereochemistry (cis/trans=97:3), the cis-substrate
gives rise to cis/trans-24 with significantly lower
stereo-retention indicating competing pathways lead-
ing to the formation of this product.[20]
All new compounds were completely characterized
by IR/NMR spectroscopic techniques, and high-reso-
lution mass analyses. In addition, the structures of 22
and 25 were also confirmed by X-ray analyses
(Figure 4, bottom). In the determined molecular
structures, the same mutual orientation of the sulfur
lone pair and the cyclic sulfite ring substituents was
found as revealed for 13 (Figure 3).
In order to investigate further the potential of these
cyclic sulfites in organic synthesis, we considered the
formation of aziridines by first oxidizing the respec-
tive sulfites to their sulfates.[12a] This oxidation could
be simply achieved by NaIO4 using RuCl3 as catalyst.
The cyclic sulfates are then easily ring-opened by
amines allowing us to form (in situ) their linear
amino-sulfates which undergo base-assisted ring-clo-
sure to give the N-substituted aziridines 30–32 in ap-
preciable yields. These Wecker-type cyclizations are
in general accompanied by side-product formation,
and typically the amino alcohol product (Scheme 2,
top) is found in the crude reaction mixtures.[21]
Aziridines 30 and 31 are known compounds for
which, however, do not exist many preparative meth-
Figure 4. Synthesis of cyclic sulfites 19–29 from internal ep-
oxides using ex situ generated SO2. Conditions (unless stated
otherwise): complex C (1.0 mol%), NBu4Br (2.5 mol%),
CH3CN (1.0 mL), 708C, 16 h. Reported yields are isolated
ones after column purification. The cis/trans assignments
1
and dr ratios were determined by H NMR. Note that for
the cis/trans mixtures, only the major isomer is drawn in the
Figure.
the conformational complexity and flexibility, and this
should facilitate its conversion into the cyclic sulfite.
The scope of products displayed in Figure 4 shows
that epoxides with different ring sizes are suitable
coupling partners for SO2, and as far as we are aware
our newly developed catalytic process is the first to
Scheme 2. Synthesis of N-substituted aziridines 30–32 from
cyclic sulfites through an oxidation, aminolysis and ring-clo-
exhibit such general potential towards the formation sure sequence.
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ods.[12a,22] More importantly, aziridine 32 has not been
reported before and shows that the present modular
protocol thus offers new potential towards a wider
range of N-substituted aziridines including the use of
poorly nucleophilic aromatic amines.
to 708C and stirred for 12 h after which the product was ex-
tracted by ethyl acetate, concentrated and purified by
column chromatography. The corresponding analytical data
and NMR/IR spectra for 30–32 are reported in the Support-
ing Information.
Conclusions
Crystallographic Studies
We here report on a new catalytic procedure for the
formation of functional cyclic sulfites from a wide
range of terminal and internal epoxides and SO2
under productive Al(III) catalysis. The process is
characterized by its operational simplicity, unprece-
dented product scope and mild reaction conditions.
Furthermore, the synthetic potential of these cyclic
sulfites was further demonstrated by application in N-
substituted aziridine synthesis. The present work thus
further expands the use of small molecules such as
SO2 in preparative chemistry, and offers new potential
towards the construction of valuable chemicals.[23]
The measured crystal was stable under atmospheric condi-
tions; nevertheless it was treated under inert conditions im-
mersed in perfluoro-polyether as protecting oil for manipu-
lation. Data Collection: measurements were made on
a Bruker-Nonius diffractometer equipped with an APPEX
II 4 K CCD area detector, a FR591 rotating anode with Mo
Ka radiation, Montel mirrors and a Kryoflex low tempera-
ture device (T=À1738C). Full-sphere data collection was
used with w and f scans. Programs used: data collection
Apex2V2011.3 (Bruker-Nonius 2008), data reduction
Saint+Version 7.60 A (Bruker AXS 2008) and absorption
correction SADABS V. 2008–1 (2008). Structure solution:
SHELXTL Version 6.10 (Sheldrick, 2000) was used.[24] Struc-
ture refinement: SHELXTL-97-UNIX VERSION.
Crystal data for cyclic sulfite 13: C14H12SO3, Mr =260.30,
monoclinic, P2(1), a=5.7150(4) ꢄ, b=39.165(4) ꢄ, c=
Experimental Section
5.8138(4) ꢄ,
a=908,
b=114.065(9)8,
g=908,
V=
1188.20(19) ꢄ3, Z=4, 1=1.455 mgMÀ3, m=0.269 mmÀ1, l=
0.71073 ꢄ, T=100(2) K, F(000)=544, crystal size=0.20ꢅ
0.08ꢅ0.01 mm, q(min)=3.128, q(max)=26.698, 12372 reflec-
tions collected, 4368 reflections unique (Rint =0.0682),
GoF=1.039, R1 =0.0734 and wR2 =0.1811 [I> 2s(I)], R1 =
0.0876 and wR2 =0.1892 (all indices), min/max residual den-
sity=À0.605/1.116 [e·ꢄÀ3]. Completeness to q(26.698)=
91.0%.
Crystal data for cyclic sulfite 22: C4H6SO4, Mr =150.15,
monoclinic, P21/c, a=4.3700(3) ꢄ, b=11.7211(8) ꢄ, c=
11.1311(7) ꢄ, a=908, b=100.0185(19)8, g=908, V=
561.45(6) ꢄ3, Z=4, 1=1.776 mgMÀ3, m=0.507 mmÀ1, l=
0.71073 ꢄ, T=100(2) K, F(000)=312, crystal size=0.30ꢅ
0.15ꢅ0.04 mm, q(min)=2.548, q(max)=32.518, 6736 reflec-
tions collected, 1865 reflections unique (Rint =0.0365),
GoF=1.046, R1 =0.0316 and wR2 =0.0830 [I> 2s(I)], R1 =
0.0393 and wR2 =0.0887 (all indices), min/max residual den-
sity=À0.312/0.544 [e·ꢄÀ3]. Completeness to q(32.518)=
91.5%.
Crystal data for cyclic sulfite 25: C10H10SO3, Mr =210.24,
monoclinic, P21/c, a=7.4377(13) ꢄ, b=11.56071(19) ꢄ, c=
21.1227(4) ꢄ, a=908, b=90.0436(16)8, g=908, V=
1816.24(5) ꢄ3, Z=8, 1=1.538 mgMÀ3, m=0.331 mmÀ1, l=
0.71073 ꢄ, T=100(2) K, F(000)=880, crystal size=0.20ꢅ
0.10ꢅ0.10 mm, q(min)=2.018, q(max)=36.948, 39202 reflec-
tions collected, 8857 reflections unique (Rint =0.0294),
GoF=1.081, R1 =0.0312 and wR2 =0.0900 [I> 2s(I)], R1 =
0.0358 and wR2 =0.0942 (all indices), min/max residual den-
sity=À0.387/0.694 [e·ꢄÀ3]. Completeness to q(36.948)=
96.3%.
CCDC 1494964 (13), CCDC 1494963 (22) and CCDC
1494965 (25) contain the supplementary crystallographic
data for the above compounds. These data can be obtained
free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
Cyclic Sulfite Synthesis
Copper powder (9.0 mmol) was added to sulfuric acid
(10 mL) and then heated to 908C. This reaction vessel was
connected to another through a Teflon tube and an over-
pressure “trap” containing a solution of NaOH (2M). The
main reactor was charged with a solution of the epoxide
(3.0 mmol), complex C (0.5–1.0 mol%) and NBu4I (2.5–
5.0 mol%) in acetonitrile (1.0 mL), and a gentle flow of N2
was adjusted such that the ex situ formed SO2 was transport-
ed towards the reactor containing the substrate/catalyst.
Once the SO2 started to form (bubbles), the reaction flask
was heated to 508C and the mixture stirred for 3 h (terminal
epoxides) or 16 h (internal epoxides). Thereafter, the sol-
vent was removed and the product purified by column chro-
matography. The corresponding analytical data and NMR/
IR spectra for 1–29 are reported in the Supporting Informa-
tion.
Cyclic Sulfate Synthesis
The respective cyclic sulfite (1.0 mmol) was dissolved into
acetonitrile (1.0 mL) and cooled down to 08C. Then NaIO4
(1.2 equiv), RuCl3 (1.0 mol%) and pre-cooled water
(1.0 mL) were added to the reaction mixture. The mixture
was stirred at room temperature for 15 min. Then the prod-
uct was extracted with ethyl acetate and dried over anhy-
drous sodium sulfate. The crude product thus obtained was
purified by column chromatography.
Aziridine Synthesis
The respective cyclic sulfate (1.0 mmol) was combined with
the corresponding amine (1.2 mmol) and this mixture was
stirred for 15 min, whereafter toluene (2.0 mL) and NaOH
(6M, 2.0 mL) were added. This biphasic mixture was heated
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Chem. 2010, 14, 401–432. For an early review, see:
e) B. B. Lohray, Synthesis 1992, 1035–1052.
Acknowledgements
[8] For a few selected examples following the thionyl chlo-
ride route, see: a) A. Garcia-Granados, A. Parra, F.
Rivas, A. J. Segovia, J. Org. Chem. 2007, 72, 643–646;
b) S. Tanaka, Y. Sugihara, A. Sakamoto, A. Ishii, J. Na-
kayama, Heteroat. Chem. 2003, 14, 587–595; c) C. Har-
dacre, I. Messina, M. E. Migaud, K. A. Ness, S. E.
Norman, Tetrahedron 2009, 65, 6341–6347; d) Y. Gao,
K. B. Sharpless, J. Am. Chem. Soc. 1988, 110, 7538–
7539.
We thank ICIQ, ICREA, and the Spanish Ministerio de
Economꢀa y Competitividad (MINECO) through project
CTQ2014-60419-R, and support through Severo Ochoa Ex-
cellence Accreditation 2014–2018 (SEV-2013–0319). VL
thanks the MINECO for an FPU pre-doctoral fellowship. Dr.
Noemꢀ Cabello is thanked for the MS studies.
[9] Cyclic sulfite synthesis from epoxides and SO2 using
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Aluminum-Catalyzed Formation of Functional 1,3,2-
Dioxathiolane 2-Oxides from Sulfur Dioxide: An Easy
Entry towards N-Substituted Aziridines
9
Adv. Synth. Catal. 2016, 358, 1 – 9
Victor Laserna, Eddy Martin, Eduardo C. Escudero-Adꢀn,
Arjan W. Kleij*
Adv. Synth. Catal. 0000, 000, 0 – 0
9
ꢃ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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These are not the final page numbers!