The base-mediated cyclization of selected benzyl alkynyl sulfones with aromatic aldehydes: Novel synthetic access to aryl-substituted 5,6-dihydro-1,4-oxathiin S,S -dioxides

Article abstract of DOI:10.1080/17415993.2012.719509

Based on an unexpected product isolated during the LDA-mediated intramolecular cyclization of a benzyl alkynyl sulfones, a conceptually new cyclization method for the formation of 5,6-dihydro-1,4-oxathiin S,S-dioxides is demonstrated. The reaction affords

Full text of DOI:10.1080/17415993.2012.719509

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The base-mediated cyclization of
selected benzyl alkynyl sulfones
with aromatic aldehydes: novel
synthetic access to aryl-substituted 5,6-
dihydro-1,4-oxathiin S,S-dioxides
Lilly U. Ho a , Mohanad Gh. Shkoor a , M. Selim Hossain a , Matthew
C. Deen a , Dmitriy V. Soldatov a & Adrian L. Schwan a
a Department of Chemistry, University of Guelph, Guelph, ON,
Canada, N1G 2W1
Version of record first published: 18 Sep 2012.
To cite this article: Lilly U. Ho , Mohanad Gh. Shkoor , M. Selim Hossain , Matthew C. Deen , Dmitriy
V. Soldatov & Adrian L. Schwan (2013): The base-mediated cyclization of selected benzyl alkynyl
sulfones with aromatic aldehydes: novel synthetic access to aryl-substituted 5,6-dihydro-1,4-
oxathiin S,S-dioxides, Journal of Sulfur Chemistry, 34:1-2, 79-87
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Journal of Sulfur Chemistry, 2013
Vol. 34, Nos. 1–2, 79–87, http://dx.doi.org/10.1080/17415993.2012.719509
SHORT COMMUNICATION
The base-mediated cyclization of selected benzyl alkynyl
sulfones with aromatic aldehydes: novel synthetic access to
aryl-substituted 5,6-dihydro-1,4-oxathiin S,S-dioxides
Lilly U. Ho, Mohanad Gh. Shkoor, M. Selim Hossain, Matthew C. Deen, Dmitriy V. Soldatov†
and Adrian L. Schwan*
Department of Chemistry, University of Guelph, Guelph, ON, Canada N1G 2W1
(Received 10 July 2012; final version received 6 August 2012)
On the occasion of his 70th birthday, this paper is dedicated to Professor Eric Block, a valued mentor and a recognized
leader in the international sulfur community.
Based on an unexpected product isolated during the LDA-mediated intramolecular cyclization of a benzyl
alkynyl sulfones, a conceptually new cyclization method for the formation of 5,6-dihydro-1,4-oxathiin
S,S-dioxides is demonstrated. The reaction affords products with (het)aryl groups at the 5- and 6-positions
in 7–54% yield.
R
O O
S
1. base
Ar'
Ar
THF
2. ArCHO
Ar'
SO2
O
R
7-54%
Keywords: sulfone; cyclization; 1,4-oxathiin S,S-dioxides; base-mediated; alkyne
1. Introduction
In a previous publication, the Schwan group introduced the LDA-mediated intramolecular cycliza-
tion of selected benzyl alkyl sulfones (1). In that communication, we indicated that either direct
or indirect formation of a carbanion at the benzylic position brought about a new mode for the
formation of 1H-2-benzothiopyran S,S-dioxides (isothiochroman 2,2-dioxides) (2). The cycliza-
tion has similarities and differences compared to established anionic cyclizations involving the
dearomatization of aryl sulfones (3–7).
Herein, we introduce a recently discovered product from an intramolecular cyclization attempt
and demonstrate, on a proof-of-principle basis, that one of the possible reactions involved in its
formation can serve as an inspiration for the preparation of 5,6-dihydro-1,4-oxathiin S, S-dioxides.
*Corresponding author. Email: schwan@uoguelph.ca
†Author to whom correspondence regarding the X-ray analysis should be directed: Email: dsoldato@uoguelph.ca.
© 2013 Taylor & Francis

80 L.U. Ho et al.
2. Results and discussion
While pursuing the scope of the aforementioned intramolecular cyclization chemistry of benzyl
alkyl sulfones, it was discovered that cyclization was severely hindered by placement of a t-butyl
group on the alkyne opposite the sulfone (1). Whereas 2a could be formed in 59% yield by
cyclization, compound 2b was not observed at all. The reaction mixture did, however, yield a
different and unexpected compound as a major product (Scheme 1).
Scheme 1. Divergent directions of benzyl alkynyl sulfone cyclizations.
That main product, eventually identified as 3, was isolated and purified and a single-crystal
X-ray diffraction study was conducted to confirm the molecular structure and elucidate the
molecular geometry. The study revealed two crystallographically different, but chemically iden-
tical molecules of 3 in the crystal structure (referred to as molecules 3A and 3B further in the
text). Molecule 3A is shown in Figure 1. The distances S1A–C1A (1.806(8) Å), C1A–C2A
(1.55(1) Å), C2A–O3A (1.457(9) Å), O3A–C3A (1.342(9) Å), C3A–C4A (1.36(1) Å) and C4A–
S1A (1.713(9)Å) are within the expected range and confirm the double character of the C3A–C4A
bond. The corresponding distances in the molecule 3B are 1.801(8), 1.54(1), 1.445(9), 1.351(9),
1.34(1) and 1.719(9)Å. Two crystal structures showing the same six-membered ring fragment with
the sulfone group and the adjacent double bond have been reported previously (8, 9). The overall
geometry of the ring is similar in these structures. In the 3,3,5,6-tetraphenyl-2-one derivative (8),
the S–C(sp3), C(sp3)–C(sp3), C(sp3)–O, O–C(sp2), C(sp2)–C(sp2) and C(sp2)–S distances are
Figure 1. ORTEP view of molecule 3A as found in the crystal structure of 3. The thermal ellipsoids are at the 50%
probability level.

Journal of Sulfur Chemistry 81
1.838(6), 1.541(8), 1.364(7), 1.383(7), 1.341(8) and 1.761(6) Å, respectively. The correspond-
ing distances for another structure, systemic fungicide oxycarboxin (9), are 1.761(4), 1.509(5),
1.432(5), 1.346(5), 1.357(5) and 1.754(4) Å. As expected, the sulfone S atom and the O atom of
3
=
the ring are coplanar with the C C double bond in 3 (within 0.005Å), while the two C(sp ) atoms
deviate from the plane by 0.3–0.5 Å. The conformational geometry of the molecule is quite rigid:
the dihedral angles between the least-squares plane of the S-containing ring and the phenyl rings
C5A–C10A and C11A–C16A are 89.6(2)◦and 69.1(3)◦, respectively, while the corresponding
angles in molecule B are 88.1(3)◦and 67.9(3)◦. The arrangement of the molecules in the crystal
is consistent with van der Waals type of packing and the only found short intermolecular contact
is between I2A and I2B of 3.8 Å.
The mode of formation of heterocycle 3 presumably follows the principles of Scheme 2, where
=
R2C Y is o-iodobenzaldehyde. Whereas the mechanism for the apparent in situ formation of
the aldehyde from 1b in the reaction mixture is still under investigation, the proposed mode of
formation of 3 provided the impetus to evaluate the chemistry of Scheme 2 directly. The chemistry
=
would provide a facile synthetic access to the 5,6-dihydro-1,4-oxathiin S,S-dioxide (Y O). The
oxathiin S,S-dioxide heterocyclic core is central to a well-recognized family of fungicides (10–
12). Whereas a variety of synthetic approaches to the ring system are documented (10, 13–16),
generally applicable methodologies are rare, as are accesses to substrates with multiple aryl
substituents (14).
R'
O O
S
O O
S
H+
R
2C=Y
H
SO2
R
2C
R'
Y-
R
2C
Y
R'
–
Scheme 2. Proposed formation of sulfone-containing heterocycles.
The premise of Scheme 2 forms the model for a conceptually new preparation of 5,6-dihydro-
1,4-oxathiin S,S-dioxides and this chemistry was pursued by our group. Specifically, compounds
of type 1b were deprotonated and an aldehyde was then introduced to effect electrophilic capture
and subsequent intramolecular conjugate addition to the triple bond. The key to establishing the
chemistry is to intercept the benzyl anion prior to its intramolecular cyclization or competitive
polymerization (1). Several experiments were carried out at temperatures below −10◦C in order
to probe incorporation of aldehyde. For several reaction temperatures, a cyclization product was
observed, but the mixture still contained significant starting material. Eventually, the selected
conditions involved the exposure of sulfones 1 in THF to base (LDA or nBuLi, vide infra) at
−35◦C for 2 h. Introduction of the aldehyde in THF was followed by stirring overnight at −35◦C,
followed by aq. acid quench at the same temperature. Under these conditions, the amount of
starting sulfone 1 that typically remained was 0–40%.
Products 4 were isolated after multiple flash chromatographies and were typically characterized
by diagnostic peaks in the proton NMR. Specifically, the lone vinylic proton was evident as
a sharp singlet in the 5.85–6.46 ppm range. The two lone methine protons appeared each as
1
1
doublets in the 5.81–6.38 and 4.81–5.57 ppm regions of the H NMR spectrum. Their H–1H
coupling constant was typically in the 11.4–11.7 Hz range, in keeping with that observed for 3
− − −
(11.4 Hz). Indeed the H C C H dihedral angle of the trans-disposed protons of the oxathiin ring
skeleton established by the X-ray crystal structure analysis [168.2(7)◦(3A) and 170.2(7)◦(3B)]
are consistent with the large 1H–1H coupling constant according to the Karplus curve. Thus, the
5,6-(het)aryl groups of all cyclization products 4a–c, e–g possessed the trans-stereochemistry.

82 L.U. Ho et al.
Table 1. Formation of 5,6-dihydro-1,4-oxathiin S,S-dioxides (2) by reaction of alkynyl sulfones 1 with aldehydes.
Starting sulfone
Aldehyde/base
5,6-dihydro-1,4-oxathiin S,S-dioxide % Yielda
1
2
Benzaldehyde/nBuLi
4a:
54 (57)
19 (22)
Furfural/nBuLi
4b:
4c:
Ph
SO2
7b
1c
3
4
4-Nitro-benzaldehyde/nBuLi
n−Butyraldehyde/nBuLi
0c
4d:
O O
S
2-I-C6H4
5
7
1a
Benzaldehyde/LDA
Benzaldehyde/LDA
11
4e:
4f:
H
H
O
Ph
Ph
1b
25 (37)
Ph
8
Benzaldehyde/nBuLi
25d
4g:
SO2
S
1d
Notes: aIsolated yield is indicated. Yield in parenthesis indicates yield based on the consumed starting material.
bLow intensity peaks were observed in the 1H NMR that could be attributable to a minor stereoisomer of 4c.
cNo cyclization product was obtained.
dProduct could not be obtained in pure form. Yield is estimated from the 1H NMR spectrum of the crude reaction mixture. See Section 5
for partial characterization of 4g.
13C NMR and IR spectroscopies and mass spectrometry data are also fully consistent with the
assigned structures.
Judging by the outcome of the reactions, the identity of the base exhibited little influence
on the chemical yield. nBuLi was the most convenient, but a control experiment indicated that

Journal of Sulfur Chemistry 83
nBuLi prefers to react with an o-iodobenzyl substrate by way of lithium–halogen exchange,
as evidenced by the intramolecular cyclization of 1e to 2e (Scheme 3). Hence, o-iodobenzyl
containing substrates 1a and 1b were treated with LDA.
Scheme 3. Intramolecular cyclization from chemoselective reaction of nBuLi with o-iodobenzyl
sulfone 1e.
Assuming equally effective benzyl anion formation with either LDA or nBuLi, the cyclization
proceeded in poor to fair yields with a number of substrates (Table 1). NMR evidence suggests
polymerization was competitive in a number of instances. Moreover, difficult separations also led
to reduced yields. Since the optimized conditions for 4a and benzaldehyde provided the best yield,
it is possible that each of the other reactions requires a separate optimization assessment. Thienyl
containing substrate 4d reacted with benzaldehyde only in low yield; the product (4g) could not be
obtained pure, but diagnostic NMR and MS data indicated some cyclization occurred. The reaction
proved unsuitable for aliphatic aldehydes (Table 1, Entry 4). The reaction is also not amenable
=
= =
to replacement of the aromatic aldehydes with carbon disulfide (Scheme 2, R2C Y = S C S),
=
=
an N-phenyl aldimine (Scheme 2, R2C Y = PhCH NPh) or phenyl isothiocyanate (Scheme 2,
=
R2C Y = PhNCS): no 1,4-dithiin or 1,4-thiazine based heterocycles were obtained in those trials.
In the latter instance, with sulfone 1c as the starting substrate, only after warming the product of
fully intramolecular cyclization was observed.
3. Conclusion
The chemistry of this communication successfully demonstrates the principle that the benzyl anion
derived from selected benzyl alkynyl sulfones can be captured with aromatic aldehydes for the
eventual formation of 5,6-di(het)aryl-5,6-dihydro-1,4-oxathiin S,S-dioxides, albeit in poor to fair
yields. Clearly, additional optimization is required to increase the yields, and there is potential
for cyclization with catalytic base. The chemistry suggests that the inclusion of an aldehyde
unit may be a component of the mechanism leading to the unexpected formation of a 5,6-di-(2-
iodophenyl)-5,6-dihydro-1,4-oxathiin S,S-dioxide (3) when o-iodobenzyl 3,3-dimethylbutynyl
sulfone (1b) was treated with base.
4. Experimental
Flash column chromatography was performed with silica gel particle size 30–63 (mesh 230–
400) supplied by Silicycle®. 1H NMR and 13C NMR spectra were recorded on a Bruker Avance
1
1
300 (300 MHz H), a Bruker Avance 400 (400 MHz H, 100.6 MHz 13C) or a Bruker Avance
1
600 (600 MHz H, 150.9 MHz 13C). High-resolution mass spectrometry was carried out using
a Q-TOF micro (Waters, Cambridge, MA, USA). Samples were infused at a concentration of
approximately 10 μM in 9:1 acetonitrile:water with 0.1 mM ammonium acetate at a flow rate
of 5 μL/min through an ESI source in positive ionization mode with a spray voltage of 3700V.

84 L.U. Ho et al.
Gentle source conditions including a cone voltage of 20V and a collision cell voltage of 8V were
used with N2 nebulizer (300 l/h) and cone (30 l/h) gas. External mass calibration was carried out
using [Glu1]-Fibrinopeptide.
4.1. Formation of 1,4-oxathiin S,S-dioxide 3
Freshly prepared LDA (1.00 equiv.) in THF was slowly added to a solution of 2-iodobenzyl-
3,3-dimethyl-1-butynyl sulfone (1b [R = tBu], 0.500 g, 1.38 mmol) (0.05 M concentration of
substrate, 27.60 ml of THF) at −78◦C. The cold bath was removed and the reaction mixture
was permitted to warm to rt for overnight. The mixture was quenched with saturated aqueous
NH4Cl. The layers were separated, and the aqueous layer was extracted with EtOAc (3 × 10 ml).
The combined organic layers were washed with brine, dried over MgSO4 and concentrated under
reduced pressure.After flash chromatography (hexanes and EtOAc) and recrystallization (hexanes
and EtOAc), 0.201 g of 3 was isolated (68% based on the recovery of 0.139 g of the starting
material). Mp: 184–185◦C. 1H NMR (400 MHz, CDCl3): δ: 7.77 (m, 2H), 7.46 (dd, J = 1.5 and
7.9 Hz, 1H), 7.37 (dd, J = 1.6 and 7.9 Hz, 1H), 7.31–7.22 (m, 2H), 6.97–6.89 (m, 2H), 6.38 (d,
J = 11.4 Hz, 1H), 5.93 (s, 1H), 5.51 (d, J = 11.4 Hz, 1H), 1.18 (s, 9H). 13C NMR (100.6 MHz,
CDCl3): δ: 171.14, 140.15, 139.87, 137.15, 131.44, 131.11, 130.68, 129.30, 128.82, 128.75,
128.21, 103.87, 101.38, 100.36, 85.96, 69.47, 37.21, 27.41. IR (neat, νmax): 2969, 1608, 1471,
1305, 1136, 1101, 1013, 911 cm−1. ESI HRMS, calculated for [C20H20SO3I2+H]+: 594.9296;
found: 594.9374.
4.2. X-ray analysis of 3
Acrystalof 3(thincolorlesssheet, 0.4×0.2×0.01mm)wasselectedfromabulkproductobtained
bycrystallizationfromethylacetate–hexane.Thecrystalwasmountedonthetipofaglassfiberand
studied at room temperature on a SuperNovaAgilent single-crystal X-ray diffractometer equipped
with a microfocus CuKα (λ = 1.54184 Å) radiation source and Atlas CCD detector. Diffraction
intensity data were collected using ω-scan to the maximum 2θ angle of 130◦(resolution of 0.85Å),
with the redundancy factor of 4. The unit cell parameters were refined using the entire data set.
The data were processed using CrysAlisPro software (17).Absorption corrections were applied
using the multiscan method. Since the crystal was very thin (<0.01 mm) and displayed lower
quality data, the SADABS software (18) was used to introduce the absorption correction through
a special treatment procedure for plate-like crystals (face {010}, min glancing angle 5◦). The
structure was solved (direct methods) and refined (full-matrix least-squares on F2) using SIR-92
(19) and SHELXL-97 (20). Non-hydrogen atoms were refined anisotropically, while hydrogen
atoms were introduced at calculated positions as riding on their corresponding carbon atoms and
refined isotropically.All significant residual extrema on the final electron density map were located
near the iodine atoms. Geometric calculations were carried out using the WinGX (21) and Olex
(22) software packages and molecular graphics was prepared using ORTEP-3 for Windows (23).
Crystal data: C20H20I2O3S, formula weight 594.22; temperature of study 293(2) K; tri-
clinic, P−1; a = 10.347(1), b = 12.185(1), c = 17.087(2) Å; α = 95.87(2)◦, β = 90.05(2)◦,
γ = 101.89(2)◦; V = 2096.5(4) Å3; Z = 4; Dcalc = 1.883 g/cm3; µ (CuKα) = 24.63 mm−1
;
F(000) = 1144 e; reflections collected/unique 23565/6932 (Rint = 0.058); refinement of 476
parameters with full-matrix least-squares on F2; final R indices [5393 data with I > 2σI]
R1 = 0.074, wR2 = 0.197; goodness-of-fit 1.097. Full crystallographic data including a CIF file
have been deposited with the Cambridge Crystallographic Data Centre with the deposition number
CCDC 886549 and can be obtained free of charge via http://www.ccdc.cam.ac.uk/data_request/cif
or by e-mail deposit@ccdc.cam.ac.uk.

Journal of Sulfur Chemistry 85
4.3. Preparation of sulfones 1
Sulfones 1 were prepared from the corresponding sulfides (1,24) by oxidation. Compounds 1a–d
have been previously reported (1).
4.4. General procedure for preparation of 1,4-oxathiin S,S-dioxides 4
To a solution of starting sulfone in THF (1.0 equiv., 0.05 M) at −78◦C, nBuLi (1.2 equiv., 1.6 M
in hexanes) or LDA (1.2 equiv. in THF) was added dropwise. The mixture was allowed to warm
up to −35◦C and stirred for 2 h. A solution of the aldehyde in THF (2.0 equiv., 0.4 M) was
added to the reaction mixture which was then left to stir at −35◦C overnight. The reaction was
quenched with sat. aq. NH4Cl at −35◦C, and the aq. layer was extracted with EtOAc (3 × 10 ml).
The combined organic layers were washed with H2O, brine, dried over MgSO4, filtered and
concentrated under vacuum. Two to three flash chromatography separations on silica gel (EtOAc
or ethyl ether/hexane: 5–15%:95–85%) gave pure product, unless otherwise noted.
4.4.1. 3,5,6-Triphenyl-5,6-dihydro-1,4-oxathiin S,S-dioxide 4a
From sulfone 1c and benzaldehyde, 1,4-oxathiin S,S-dioxide 4a was obtained as a white solid,
54% yield; mp = 187–189◦C (dec.). 1H NMR (600 MHz, CDCl3), δ: 7.47–7.25 (m, 15H), 6.46
(s, 1H), 6.18 (d, J = 11.7 Hz, 1H), 4.81 (d, J = 11.7 Hz, 1H); 13C NMR (150.9 MHz, CDCl3), δ:
159.49, 134.92, 132.03, 131.52, 131.13, 129.47, 129.29, 128.79, 128.71, 128.64, 128.12, 126.38,
125.42, 101.37, 83.08, 67.96; IR (neat, νmax): 3067, 1609, 1575, 1364, 1283, 1127, 1078, 910,
695 cm−1; ESI HRMS, calculated for [C22H18SO3+H]+: 363.1050; found: 363.1066.
4.4.2. 3,6-Diphenyl-5-(2-furyl)-5,6-dihydro-1,4-oxathiin S,S-dioxide 4b
From sulfone 1c and furfural, 1,4-oxathiin S,S-dioxide 4b was obtained as a white solid, 19%
yield; mp = 144–146◦C (dec.). 1H NMR (600 MHz, CDCl3), δ: 7.63 (d, J = 7.8 Hz, 2H), 7.48–
7.26 (m, 9H), 6.42 (s, 1H), 6.39 (s, 1H), 6.24, (d, J = 11.7 Hz, 1H), 6.23 (s, 1H), 4.96 (d, J =
11.7 Hz, 1H); 13C NMR (150.9 MHz, CDCl3), δ: 159.25, 147.37, 143.91, 131.94, 131.56, 130.72,
129.44, 128.44, 128.79, 128.63, 126.43, 125.20, 112.18, 110.49, 101.52, 65.61; IR (neat, νmax):
3070, 1609, 1575, 1496, 1283, 1127, 1078 cm−1; ESI HRMS, calculated for [C20H16SO4+H]+:
353.0843; found: 353.0878.
4.4.3. 3,6-Diphenyl-5-(4-nitrophenyl)-5,6-dihydro-1,4-oxathiin S,S-dioxide 4c
From sulfone 1c and 4-nitrobenzaldehyde, 1,4-oxathiin S,S-dioxide 4c was obtained as a pale pink
solid, 7% yield; mp = 213–215◦C (dec.). 1H NMR (400 MHz, CDCl3), δ: 8.14 (d, J = 8.8 Hz,
2H) 7.63 (d, J = 7.2 Hz, 2H), 7.55–7.28 (m, 10H), 6.52 (s, 1H), 6.31 (d, J = 11.6 Hz, 1H),
4.79 (d, J = 11.6 Hz, 1H); 13C NMR (100.6 MHz, CDCl3), δ: 159.13, 148.30, 141.65, 131.80,
131.55, 130.92, 129.83, 129.02, 128.96, 128.92, 126.28, 124.73, 123.90, 102.02, 81.90, 67.82;
IR (neat, νmax): 3072, 1609, 1523, 1349, 1281, 1127, 1086 cm−1; ESI HRMS, calculated for
[C22H17SO5N+H]+: 408.0901; found: 408.0923. Low-intensity peaks were observed in the 1H
NMR that could be attributable to a minor stereoisomer of 4c.

86 L.U. Ho et al.
4.4.4. 3,5-Diphenyl-6-(2-iodophenyl)-5,6-dihydro-1,4-oxathiin S,S-dioxide 4e
Fromsulfone 1a andbenzaldehyde, 1,4-oxathiinS,S-dioxide 4e wasobtainedasawhitesolid, 11%
yield. 1H NMR (600 MHz, CDCl3), δ: 7.71 (dd, J = 8.0, 1.0 Hz, 1H), 7.58 (d, J = 7.4 Hz, 2H),
7.46–7.02 (m, 11H), 6.85 (m, 1H), 6.39 (s, 1H), 6.07 (d, J = 11.4 Hz, 1H), 5.57 (d, J = 11.4 Hz,
1H); 13C NMR (150.9 MHz, CDCl3), δ: 159.48, 140.29, 134.34, 131.91, 131.56, 131.27, 130.69,
129,67, 129.38, 128.78, 128.67, 128.27, 128.06, 126.44, 104.48, 101.69, 83.94, 70.12; IR (neat,
ν
max): 3068, 2931, 1609, 1575, 1495, 1451, 1307, 1283, 1120, 1078 cm−1; ESI HRMS, calculated
for [C22H17SO3I+H]+: 489.0016; found: 488.9979.
4.4.5. 3-(t-Butyl)-6-(2-iodophenyl)-5-phenyl-5,6-dihydro-1,4-oxathiin S,S-dioxide 4f
From sulfone 1b and benzaldehyde, 1,4-oxathiin S,S-dioxide 4f was obtained as a white solid,
25% yield; mp = 180–182◦C (dec.). 1H NMR (600 MHz, CDCl3), δ: 7.66 (dd, J = 8.4, 1.2 Hz,
1H), 7.42 (dd, J = 8.1, 1.8 Hz, 1H), 7.20–7.17 (m, 6H), 6.82 (dt, J = 7.8, 1.2 Hz, 1H), 5.85 (s,
1H), 5.81 (d, J = 11.5 Hz, 1H), 5.19 (d, J = 11.5 Hz, 1H), 1.12 (s, 9H); 13C NMR (150.9 MHz,
CDCl3), δ: 171.40, 140.25, 134.62, 131.14, 130.62, 129.52, 129.48, 128.56, 128.03, 127.98,
104.45, 100.08, 83.45, 69.75, 37.27, 27.48; IR (neat, νmax): 2967, 1608, 1468, 1305, 1287, 1218,
1136, 1103 cm−1; ESI HRMS, calculated for [C20H21SO3I+H]+: 469.0329; found: 469.0310.
4.4.6. 3,5-Diphenyl-6-(2-thienyl)-5,6-dihydro-1,4-oxathiin S,S-dioxide 4g
From sulfone 1d and benzaldehyde, 1,4-oxathiin S,S-dioxide 4g was obtained in impure form
in low yield. Estimated chemical yield: 25%. 1H NMR (300 MHz, CDCl3), δ: (partial spectrum)
6.45 (s, 1H), 6.02 (d, J = 11.7 Hz, 1H), 5.08 (d, J = 11.7 Hz, 1H); ESI HRMS, calculated for
[C20H16S2O3+H]+: 369.0614; found: 369.0628.
4.5. Intramolecular cyclization of sulfone 1e.
nBuLi (1.0 equiv., 1.83 mmol) in THF was slowly added to a solution of sulfone 1e (0.750 g,
1.83 mmol) in THF (15 ml) at −78◦C. The cold bath was removed and the reaction mixture was
permitted to warm to rt over 45 min. The mixture was quenched with saturated aqueous NH4Cl.
The layers were separated, and the aqueous layer was extracted with EtOAc (3 × 5 ml). The
combined organic layers were washed with brine, dried over MgSO4 and concentrated under
reduced pressure. The product was purified by flash chromatography (hexanes/EtOAc) followed
by recrystallization from hexanes/EtOAc to give cyclic sulfone 2e (0.250 g, 1.28 mmol, 55%) as
white crystals. mp: 99–100◦C. 1H NMR (600 MHz, CDCl3): δ: 7.54 (d, J = 8.7 Hz, 1H, Ar H),
7.45–7.36 (m, 2H, Ar H), 7.28 (d, J = 6.9 Hz, 1H, Ar H), 6.52 (s, 1H, CH), 4.35 (s, 2H, CH2),
2.32 (s, 3H, CH3). 13C NMR (150.9 MHz, CDCl3): δ: 146.26, 130.57, 130.23, 130.03, 129.09,
128.66, 126.35, 124.58, 54.73, 21.15. IR (neat, νmax): 3019, 2922, 1586, 1537, 1483, 1314, 1127,
941 cm−1. ESI HRMS, calculated for [C10H10SO2+H]+: 195.0475; found: 195.0454.
Acknowledgements
The authors are grateful to NSERC of Canada and the University of Guelph for funding in support of this research and
for funding to M.C.D. for a USRA scholarship. D.V.S. thanks CFI (Canada) and MRI (Ontario) for providing funds for
the X-ray diffraction instrumentation. M.Gh.S. thanks the Ontario MRI PDF Program for providing partial postdoctoral
support.

Journal of Sulfur Chemistry 87
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