N - P -Toluenesulfinylimidazole: A New in situ Reagent for the Mild and Efficient Synthesis of p -Toluenesulfinate Alkyl Esters and Aryl Esters

Article abstract of DOI:10.1055/a-1472-7578

A new synthetic methodology has been developed for the synthesis of sulfinate alkyl and aryl esters. The methodology involves the combination of p -toluenesulfinic acid and 1,1′-carbonyldiimidazole (CDI) to create the putative reagent sulfinylimidazole. The process spontaneously releases carbon dioxide upon the addition of the CDI to the acid suggesting the rapid formation of the proposed reagent. Reaction of this reagent with a series of alcohols (primary, secondary, and tertiary) afforded the corresponding sulfinate alkyl esters in good to excellent yields by the addition of alcohols. It was also possible to form the related sulfinate aryl esters by treating the proposed sulfinylimidazole with selected phenols (phenol, p - tert -butylphenol, and thymol). The aryl esters were formed in excellent conversion based on analysis of the 500 MHz ¹H NMR spectra of the crude reaction mixtures.

Full text of DOI:10.1055/a-1472-7578

SYNTHESIS
0
0
3
9
-
7
8
8
1
1
4
3
7
-
2
1
0
X
Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart
2021, 53, A–I
paper
A
en
J. L. Shaw et al.
Paper
Synthesis
N-p-Toluenesulfinylimidazole: A New in situ Reagent for the Mild
and Efficient Synthesis of p-Toluenesulfinate Alkyl Esters and Aryl
Esters
Jessica L. Shaw
O
S
Brad J. Austermuehle
Jordan M. Witte
O
S
OH
O
S
R
O
ROH
N
Me
Timothy R. Dorsey
Christina Delach
+
N
– CO2
– imidazole
14 examples
70–90%
Me
Me
p-toluenesulfinylimidazole
O
Christopher G. Hamaker
Shawn R. Hitchcock*
N
N
N
N
O
S
Ar
O
• Mild conditions
• Metal-free
• Isomeric sulfones not observed
• Easy chromatographic purification
• Reduced environmental impact
Department of Chemistry, Illinois State University, Normal,
IL 61790-4160, USA
hitchcock@ilstu.edu
ArOH
3 examples
84–89%
Me
Corresponding Author
Received: 09.03.2021
Accepted after revision: 01.04.2021
Published online: 01.04.2021
Kaboudin et al.
DOI: 10.1055/a-1472-7578; Art ID: ss-2021-m0119-op
C
Ni
O
E = 5 V
SH
S
Abstract A new synthetic methodology has been developed for the
synthesis of sulfinate alkyl and aryl esters. The methodology involves
the combination of p-toluenesulfinic acid and 1,1′-carbonyldiimidazole
(CDI) to create the putative reagent sulfinylimidazole. The process
spontaneously releases carbon dioxide upon the addition of the CDI to
the acid suggesting the rapid formation of the proposed reagent. Reac-
tion of this reagent with a series of alcohols (primary, secondary, and
tertiary) afforded the corresponding sulfinate alkyl esters in good to ex-
cellent yields by the addition of alcohols. It was also possible to form the
related sulfinate aryl esters by treating the proposed sulfinylimidazole
with selected phenols (phenol, p-tert-butylphenol, and thymol). The
aryl esters were formed in excellent conversion based on analysis of the
500 MHz 1H NMR spectra of the crude reaction mixtures.
OR
+
ROH
X
X
Ni(ClO4)2, 2,2'-bipyridine
CH3CN, LiClO4
1
2
Wu et al.
O
S
O
S
Me3SiCl (2.0 equiv)
CH2Cl2, 25 °C, 1 h
+
ROH
Ar
OR
Ar
ONa
4
3
Basak et al.
O
S
R'
O
S
O
N
R'
Ph3P=CHCO2Me
N
O
R
H
DMPU
95 °C
R
Keywords sulfinate ester, sulfinate aryl ester, p-toluenesulfinic acid,
1,1′-carbonyldiimidazole, sulfinylimidazole
Me
Me
5
2
Hitchcock et al.
O
S
O
S
EDC, DMAP, ROH
CH2Cl2
OR
OH
Sulfinate alkyl esters are versatile tools in the synthesis
of an array of synthetically useful sulfur compounds and
can serve as key intermediates in the preparation of chiral
sulfoxides and sulfinamides, materials that can be em-
ployed in catalytic asymmetric syntheses. The stereoselec-
tive synthesis of sulfinamides and sulfoxides has been re-
cently reviewed by Wojaczyńska and Wojaczyński.1 Sulfi-
nate esters are valuable starting materials for the
preparation of a variety of sulfinyl compounds. In this con-
text, Kaboudin2a and Wei2b independently developed the
use of electrochemistry to synthesize sulfinates (Scheme 1).
Wu and co-workers developed an improved procedure for
the synthesis of sulfinate esters using trimethylsilyl
chloride in the absence of a metal catalyst.3a–c Basak and
Me
Me
2
6
Prapurna et al.
O
S
O
O
S
NC
BF3·OEt2
OR
+
ROH
MeCN, 15–20 min
Me
Me
7
2
Sun et al.
O
O
1a) NBS, AcOH, CH2Cl2, rt
1b) R'OH
S
Me
Me
S
R
R
OR'
Me
8
9
Scheme 1 Methods for the preparation of sulfinate esters
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Georg Thieme Verlag KG, Rüdigerstraße 14, 70469 Stuttgart, Germany

B
J. L. Shaw et al.
Paper
Synthesis
co-workers disclosed a Wittig ylide-mediated degradation
of N-sulfonylhydazones as a means of preparing sulfinate
alkyl esters.4 Our research group developed a carbodiimide
approach employing 1-ethyl-(3-dimethylaminopropyl)car-
sulfinyl activation (Scheme 2). The use of CDI in the forma-
tion of esters from carboxylic acids has been well docu-
mented in the chemical literature.12–17 It is proposed that
CDI might serve as an activating agent that would act on
sulfinic acids 18 to create reactive sulfinylimidazoles 19 in
the same fashion as CDI reacts with carboxylic acids to cre-
ate acyl imidazoles 16. This pathway would be attractive in
terms of the ease of formation of the sulfinylimidazole and
would then presumably react to displace the labile imidaz-
ole group. Herein, we describe our efforts to exploit CDI as a
reagent for the efficient synthesis of sulfinate esters.
bodiimide
(EDC)
and
4-(dimethylamino)pyridine
(DMAP).5,6 Prapurna et al. prepared sulfinate alkyl esters via
the BF3·OEt2-catalyzed conversion of p-toluenesulfonyl-
methyl isocyanides.7 Sun and co-workers developed an NBS
promoted activation of tert-butyl sulfoxides as an entry
point into sulfinate alkyl esters and other sulfinyl deriva-
tives.8 There are various other synthetic methods beyond
the examples that are mentioned here.9–11
Literature
In the search for an improved methodology (ease of
preparation and purification, commercially available re-
agents, and reduced environmentally impact) for the syn-
thesis of sulfinate esters, a new method of sulfinyl group
activation was considered. Conceptually, the preparation of
sulfinate esters from sulfinic acids would require the for-
mation of a suitable leaving group for the sulfinyl group.
The introduction of suitable leaving groups had been previ-
ously demonstrated in our group by reaction of p-toluene-
sulfinic acid with a variety of activating agents including
pivaloyl chloride,11 cyanuric chloride,5 and EDC and DMAP5
(Figure 1).
O
N
N
O
N
N
O
O
15
R'OH
N
R
OH
R
OR'
R
N
14
17
16
Proposed synthesis
O
N
N
O
S
N
O
S
N
O
R'OH
S
N
R
OH
R
OR'
R
N
18
sulfinate esters 9
19
O
S
O
Scheme 2 1,1′-Carbonyldiimidazole as an activating agent
H
O
O
S
N
N
O
p-Tol
N
p-Tol
O
S
The study was initiated by reacting anhydrous p-tolue-
nesulfinic acid with 1,1′-carbonyldiimidazole in dichloro-
methane (Table 1). These reagents were combined and re-
acted together for an induction time before the addition of
the test alcohol, p-nitrobenzyl alcohol. The progress of the
reaction was determined via 500 MHz 1H NMR spectrosco-
py by comparison of the methylene protons of the unreact-
ed alcohol versus the diastereotopic protons of the nearly
formed p-nitrobenzyl sulfinate ester 2. When the p-tolue-
nesulfinic acid and CDI were combined, the reactions were
noticed to undergo bubbling, presumably representing the
loss of carbon dioxide via a mechanistic pathway similar to
that described in the case of the reaction between carboxyl-
ic acids and CDI.12–17 It was determined that the longer in-
duction time was deleterious to the overall success of the
reaction. When the induction time was 90 minutes (Table 1,
entry 1), the ratio of product to starting material was 86:14
10
12a
N
p-Tol
Cl
N
N
O
S
O
N
N
N
p-Tol
sulfinylimidazole 13
S
O
Cl
p-Tol
N
11
12b
Figure 1 Activated sulfinyl groups
Each method was successfully employed in the synthe-
sis of sulfinyl derivatives, but each methodology had limita-
tions. The use of pivaloyl chloride to create a mixed sulfinic
anhydride 10 leads to sulfinate esters but is limited in the
preparation of the related sulfinamides.11 The use of cy-
anuric chloride to create the labile O-sulfinyl 3,5-dichloro-
cyanurate 11 was limited in that it yielded sulfone by-prod-
ucts that can be troublesome to remove from the targeted
sulfinate esters by chromatography.5 The use of the
EDC/DMAP reagent combination to create an O-sulfinyli-
sourea 12 has long reaction times accompanied by the for-
mation of the by-product common to sulfinate ester syn-
thesis, namely S-p-tolyl p-toluenethiosulfonate.5 These ear-
ly examples of sulfinyl group activation served as the
motivation for the pursuit of an alternate strategy that
would allow for the effective formation of sulfinate esters.
In considering a new means of activation, the use of
1,1′-carbonyldiimidazole (CDI) became an attractive option
to achieve the stated goal of an improved pathway of
1
as determined by analysis of the H NMR spectrum of the
crude reaction mixture. In contrast, the transformation
reached a level of 98:2 favoring the formation of the prod-
uct when there was no induction time (entry 6, all reagents
added in succession). It is proposed that the putative
sulfinylimidazole intermediate 19 has a limited life-time
before some mechanism of decomposition becomes preva-
lent.
There was a concern that the reaction was completed
more quickly than the 18 hour window. Thus, another trial
was carried out wherein there was no induction time. In
© 2021. Thieme. All rights reserved. Synthesis 2021, 53, A–I

C
J. L. Shaw et al.
Paper
Synthesis
Table 1 Initial Trial Studies on the CDI-Mediated Sulfinylation
O
S
O
S
O
Ha
O
Hb
O2N
CH2OH
S
CDI, CH2Cl2
OH
N
N
6
Me
2b
Me
NO2
Me
19
Entrya
Induction time
Reaction time
Ratio product/starting materialb
1
2
3
4
5
6
7
90
60
30
15
15
0
18 h
84:16
90:10
92:8
94:6
95:5
98:2
91:9
18 h
18 h
18 h
60 min
18 h
0
60 min
a All reactions were conducted with a stoichiometric ratio 1.1:1.1:1.0 of sulfinic acid/CDI/alcohol.
b The ratio of the product to starting material was determined by analysis of the 500 MHz 1H NMR spectra.
this set of the experiments, the amount of the p-toluene-
sulfinic acid and CDI were increased to a ratio of 1.5 equiva-
lents relative to the alcohol to ensure the completion of the
reaction (Table 2). It was determined that 75 minutes was a
sufficient time to allow completion of the transformation.
Interestingly, there was no observable formation of the iso-
meric sulfone product, and there was little formation of S-
p-tolyl p-toluenethiosulfonate, a common by-product in the
synthesis of sulfinate esters or alternatively obtained in the
course of the preparation of sulfinate esters.5
viable starting materials with good yields. There was no sig-
nificant diastereoselection with these examples with the
diastereomeric ratios occurring in a nearly 1:1 ratio in all
cases as determined by 500 MHz 1H NMR spectroscopy.
There was an interest in exploring the utility of this
method in the context of an acid sensitive substrate. There
are existing methodologies for the preparation of sulfinate
esters that employ conditions that occur in the presence of
catalytic sulfuric acid10 or Lewis acids (e.g., BF3·OEt2).3c,17
and these conditions would not be compatible with such
substrates. To demonstrate the utility of this new method,
the diphenylimine of L-phenylalaninol was prepared by re-
action of L-phenylalaninol with commercially available ben-
zophenone imine (Scheme 4).18,19 The structure of the
imine 21a was confirmed by X-ray crystallography (Sup-
porting Information) as there was a concern over the iden-
tity of the crystals that had been collected from the reac-
tion via recrystallization from ethyl acetate and hexanes.
The -iminoalcohol was then reacted under the p-toluene-
sulfinic acid/CDI reaction conditions to afford a 1:1 diaste-
reomeric mixture of p-toluenesulfinate esters in 64% isolat-
ed yield.
There was also an interest in pursuing the synthesis of
sulfinate aryl esters 25, a class of sulfinate esters that are
not commonly described in the chemical literature con-
cerning sulfinate ester preparative methods.20 Menezes,
Oliveira, and co-workers explored the synthetic preparation
of sulfinate aryl esters using an acid-catalyzed sulfinate es-
terification process10 but were not able to isolate any sulfi-
nate aryl ester products (Scheme 5). It is proposed here that
the sulfinate esters may have formed as unstable products
that may degraded to the starting materials under the reac-
tion conditions. This served as the inspiration for the appli-
cation of the p-toluenesulfinic acid/CDI methodology to the
problem of the synthesis of these substrates.
Table 2 CDI-Mediated Sulfinylation with No Induction Time
O
CDI, CH2Cl2
CH2OH
S
O
6
O2N
2b
Me
NO2
Entrya
Reaction time
Ratio product/starting materialb
1
2
3
4
75 min
60 min
30 min
15 min
100:0
99:1
88:17
85:15
a All reactions were conducted with a stoichiometric ratio 1.5:1.5:1.0 of
sulfinic acid/CDI/alcohol.
b The ratio of the product to starting material was determined by analysis
of the 500 MHz 1H NMR spectroscopy.
With a methodology established, a series of sulfinate es-
ters were prepared using primary and secondary alcohols
(Scheme 3). These examples included the sterically de-
manding diphenylmethanol, which yielded the correspond-
ing sulfinate ester 2i in 64% yield. Chiral alcohols such as,
rac-1-phenyl-1-ethanol, and rac-1-phenyl-1-propanol,
L-menthol, and (S)-3-hydroxytetrahydrofuran proved to be
© 2021. Thieme. All rights reserved. Synthesis 2021, 53, A–I

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J. L. Shaw et al.
Paper
Synthesis
O
O
S
N
N
R
N
N
O
6
Me
ROH, CH2Cl2
2
O
S
O
S
O
O
S
Me
S
O
O
O
O
Me
Me
Me
Me
NO2
Me
Br
2a, 70%
2c, 90%
2d, 81%
2b, 75%
O
O
O
S
O
S
Cl
S
S
Ph
O
O
O
OBn
O
Me
Cl
Me
Me
Me
2e, 83%
2g, 81%
2f, 80%
2h, 62%
Me
O
S
Me
O
S
O
S
O
O
O
Me
Me
Me
2i, 64%
Me
2j, 81%
2k, 72%
Me
O
O
S
Me
O
S
Me
Me
O
S
O
O
O
Me
H
Me
Me
Me
2l, 85%
2m, 70%
2n, 76%
Scheme 3 Substrate scope of reactions with the p-toluenesulfinic acid/CDI reagent combination. Reagents and conditions: The sulfinic acid (1.5 equiv)
and 1,1′-carbonyldiimidazole (1.5 equiv) were reacted with the substrate (1.0 equiv) in dichloromethane. Isolated yields are shown. For 2n: the reaction
was conducted with an excess of the alcohol. For 2j–m: diastereomeric ratio was determined by 1H NMR spectroscopy.
The p-toluenesulfinic acid/CDI reagent combination was
prepared in dichloromethane at room temperature as be-
fore (Table 3). Directly after these reagents were combined,
the respective phenolic substrate [p-nitrophenol (24b); p-
tert-butylphenol (24c); p-methoxyphenol (24d); and 2-iso-
propyl-5-methylphenol (thymol) (24e)] was added. This
process afforded sulfinate aryl esters 25c–e in very good
chemical yields. The formation of the sulfinate aryl ester
based on p-nitrophenol (24b) proved to be problematic as
the collected product was revealed to be a complex mixture
1
as determined by H NMR spectroscopy. It was noted that
compounds 25c–e became impure with prolonged storage
at room temperature and proved to be difficult to purify by
flash chromatography. Analysis of the 500 MHz 1H NMR
O
S
HO
R
R
O
S
ONa
24a: R = Me
24b: R = NO2
O
Me
H2SO4, CH2Cl2, 4 Å MS, 25 °C
23
Me
25a,b
Scheme 5 Attempted synthesis of phenoxysulfinate esters by Menezes,
Scheme 4 p-Toluenesulfinylation of an acid-sensitive alcohol substrate
Oliveira, and co-workers
© 2021. Thieme. All rights reserved. Synthesis 2021, 53, A–I

E
J. L. Shaw et al.
Paper
Synthesis
spectra suggested that the sulfinate aryl esters were hydro-
lyzing to release the phenol and p-toluenesulfinic acid
starting materials. Based on this assessment, the sulfinate
aryl esters were directly characterized without purification.
Ultimately, the quality of the 500 MHz 1H NMR spectro-
scopic data of these compounds suggested that the com-
pounds could be recovered in 95% purity (see Supporting
Information). Overall, this approach of employing the p-tol-
uenesulfinic acid with CDI proved to be successful in the
synthesis of these compounds that have not received signif-
icant attention.
O
O
S
N
N
O
O
H
N
N
6
+
15
+
26
27
Me
Me
O
S
O
28
N
irreversible
nucleophilic addition/elimination
N
– CO2
H
N
N
O
O
S
R
S
N
N
19
ROH
nucleophilic addition/elimination
O
Me
Me
2
Table 3 p-Toluenesulfinate/CDI Approach to the Synthesis of p-Tolue-
nesulfinate Aryl Esters
Scheme 6 Proposed mechanism for the formation of sulfinate esters
O
R
24b–e
R
S
HO
CDI, CH2Cl2, 25 °C
O
6
lysts. The formation of the isomeric sulfone products was
not observed and the common thiosulfonate by-product
was only observed as a minor product. The method proved
to be applicable in the case of an acid-sensitive substrate as
well. In this context, the reagent combination was also suc-
cessfully employed in the synthetic preparation of a series
of sulfinate aryl esters.
Me
25b–e
Entrya Phenol
Product
Yield (%)b
1
2
3
4
p-nitrophenol (24b)
p-tert-butylphenol (24c)
p-methoxyphenol (24d)
thymol (24e)
25b
25c
25d
25e
n/ac
87
89
84
a All reactions were conducted with a stoichiometric ratio 1.5:1.5:1.0 of
sulfinic acid/CDI/alcohol/additive.
Chemical reagents were used as purchased. All reactions were con-
ducted in flame-dried glassware under a dry N2 atmosphere. Crude
reaction mixtures were purified by flash chromatography using an
automated flash chromatograph. The stationary phase was 40 g nor-
mal phase silica gel cartridges. The collected fractions were analyzed
by TLC with TLC plates coated with fluorescent indicator F254 and vi-
b The yield that is reported is based on the product obtained after ex-
traction.
c The product was not isolated. n/a: Not available.
Based on the experiments conducted, it is proposed that
the reaction mechanism proceeds by an initial proton ex-
change between the p-toluenesulfinic acid (6) and CDI (15)
(Scheme 6). In this context, the reaction is significantly
compromised when the sodium salt of p-toluenesulfinic
acid is employed. Nucleophilic addition–elimination of 26
to activated CDI 27 is presumed to lead to the formation of
p-toluenesulfinyl O-acylimidazole 28.21 There is an observ-
able evolution of gas at the beginning of the reaction sug-
gesting that this intermediate irreversibly releases carbon
dioxide and imidazole to yield the presumptive intermedi-
ate p-toluenesulfinylimidazole (19). This intermediate then
undergoes a final nucleophilic addition/elimination with
the alcohol substrate. Interestingly, there is no observed
formation of carbonates [(RO)2C=O)] in any significant
means suggesting that the reaction between the sulfinic
acid and the CDI occurs more rapidly than the reaction be-
tween the alcohol and the CDI.
1
sualized with UV light. All H and 13C NMR spectra were recorded in
CDCl3 using a Bruker Ultrashield Avance III NMR spectrometer operat-
ing at 500 MHz (or 400 MHz) for 1H NMR spectra and operating at
125 MHz (or 100 MHz), respectively. Chemical shifts were reported in
parts per million ( scale) and coupling constant (J values) are listed
in hertz (Hz). TMS was used as internal standard ( = 0). IR spectra
were recorded using NaCl plates. IR spectral values were reported in
reciprocal centimeters (cm–1) and were measured as a neat liquid, Nu-
jol mull, or as a neat liquid film from an evaporated CDCl3 solution.
For electrospray ionization high resolution mass spectrometry (ESI-
HRMS), samples were prepared in concentrations of 5–25 ppm in
HPLC grade MeOH/H2O/formic acid (1:1:0.01). Analytical data was
collected using a ThermoScientific Q-Exactive ESI mass spectrometer.
Anhydrous p-Toluenesulfinic Acid (6)
To a 500 mL Erlenmeyer flask was added p-toluenesulfinic acid sodi-
um salt hydrate (5.00 g, 28.1 mmol), Et2O (60 mL), and aq 1 M HCl (60
mL). The reaction mixture was stirred at rt for 45 min. The mixture
was placed into a separatory funnel and the layers were separated.
The Et2O layer was washed with brine (2 × 20 mL), dried (MgSO4), and
the solvents were removed by rotary evaporation under high vacuum
for 2 h. The temperature of the water bath should be no greater than
25 °C as the p-toluenesulfinic acid decomposes at temperatures of
35 °C and higher. The process yielded an average value of 3.28 g of the
corresponding anhyd p-toluenesulfinic acid. Once isolated, this mate-
rial was used directly in the following reactions.
In conclusion, the utility of the combination of p-tolue-
nesulfinic acid and 1,1′-carbonyldiimidazole has been
demonstrated in the synthesis of a series of sulfinate alkyl
esters. The methodology does not require the preparation
of synthetic precursors and does not require metal cata-
© 2021. Thieme. All rights reserved. Synthesis 2021, 53, A–I

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J. L. Shaw et al.
Paper
Synthesis
Sulfinate Esters; General Procedure
13C{1H} NMR (100 MHz, CDCl3):  = 142.6, 141.6, 138.2, 132.4, 129.6,
129.1, 128.6, 125.2, 65.6, 21.4, 21.1.
HRMS (ESI): m/z [M + Na]+ calcd for C15H16O2SNa: 283.0763; found:
283.0756.
In a flame-dried, N2-purged 100 mL round-bottomed flask equipped
with a stir bar was placed freshly prepared p-toluenesulfinic acid (6;
703 mg, 4.50 mmol) and CH2Cl2 (15 mL). A magnetic stir bar was add-
ed to provide moderate stirring throughout. To the solution was add-
ed 1,1-carbonyldiimidazole (730 mg, 4.50 mmol) in one portion, after
which significant bubbling was immediately observed. This addition
was followed by the respective alcohol/phenol (3.05 mmol) to give a
light yellow-orange solution. The reaction was allowed to sit and stir
for 75 min. After this, the reaction mixture was diluted with CH2Cl2
(80 mL) and transferred to a separatory funnel for extraction. The re-
action mixture was extracted with aq 1 M NaOH (2 × 20 mL), and the
bottom organic layer was collected. Minimal exposure of the organic
layer to the aqueous environment was sought. The organic layer was
then washed with aq 1 M HCl (20 mL), brine (20 mL), dried (MgSO4),
and gravity filtered. Solvents were removed via rotary evaporation
followed by high vacuum to afford the desired product.
The collected spectroscopic data were consistent with the spectro-
scopic data reported in the chemical literature.5
4-Bromobenzyl p-Toluenesulfinate (2d)
The product was purified by flash chromatography on silica gel using
90:10 hexanes/EtOAc as the eluent to give a white waxy solid; yield:
0.7931 g (81%).
IR (neat): 1129, 738, 688 cm–1
.
1H NMR (400 MHz, CDCl3):  = 7.60 (d, J = 8.2 Hz, 2 H), 7.43 (d, J = 8.2
Hz, 2 H), 7.33–7.35 (m, 2 H), 7.12–7.14 (m, 2 H), 4.94 (d, J = 11.7 Hz, 1
H), 4.48 (d, J = 11.7 Hz, 1 H), 2.43 (s, 3 H).
13C{1H} NMR (100 MHz, CDCl3):  = 142.9, 141.3, 134.6, 131.6, 130.0,
129.7, 125.2, 122.4, 64.4, 21.4.
HRMS (ESI): m/z [M + Na]+ calcd for C14H13BrO2SNa: 346.9712; found:
346.9705.
Methyl p-Toluenesulfinate (2a)
The p-toluenesulfinic acid (6; 586 mg, 3.75 mmol) served as the lim-
iting reactant with the use of excess MeOH (5 equiv). The product was
recovered and characterized without purification; yield: 0.447 g
(70%). Crude was isolated to give a clear colorless oil (>95% yield as
determined by analytical data).
The collected spectroscopic data were consistent with the spectro-
scopic data reported in the chemical literature.5
IR (neat): 2985, 1596, 1130, 1081, 812 cm–1
.
4-Chlorobenzyl p-Toluenesulfinate (2e)
The product was purified by flash chromatography on silica gel using
90:10 hexanes/EtOAc as the eluent to give a clear colorless oil; yield:
0.703 g (83%).
1H NMR (500 MHz, CDCl3):  = 7.60 (d, J = 8.2 Hz, 2 H), 7.35 (d, J = 7.9
Hz, 2 H), 3.49 (s, 3 H), 2.45 (s, 3 H).
13C{1H} NMR (125 MHz, CDCl3):  = 142.8, 140.9, 129.7, 125.3, 49.4,
21.4.
HRMS (ESI): m/z [M + Na]+ calcd for C8H10O2SNa: 193.0293; found:
193.0296.
IR (neat): 1129, 915, 744 cm–1
.
1H NMR (500 MHz, CDCl3):  = 7.61 (d, J = 8.2 Hz, 2 H), 7.33 (d, J = 8.2
Hz, 2 H), 7.28–7.30 (m, 2 H), 7.18–7.20 (m, 2 H), 4.96 (d, J = 11.6 Hz, 1
H), 4.49 (d, J = 11.6 Hz, 1 H), 2.43 (s, 3 H).
13C{1H} NMR (100 MHz, CDCl3):  = 142.9, 141.4, 134.2, 134.0, 129.8,
129.7, 128.6, 125.2, 64.4, 21.4.
The collected spectroscopic data were consistent with the spectro-
scopic data reported in the chemical literature.6
HRMS (ESI): m/z [M + Na]+ calcd for C14H13ClO2SNa: 303.0217; found:
303.0211.
4-Nitrobenzyl p-Toluenesulfinate (2b)
The product was purified by flash chromatography on silica gel using
90:10 hexanes/EtOAc as the eluent to give a white waxy solid; yield:
0.6588 g (75%).
The collected spectroscopic data were consistent with the spectro-
scopic data reported in the chemical literature.5
IR (neat): 1134, 817, 746 cm–1
.
2-Chlorobenzyl p-Toluenesulfinate (2f)
1H NMR (400 MHz, CDCl3):  = 8.16 (d, J = 8.2 Hz, 2 H), 7.63 (d, J = 8.2
Hz, 2 H), 7.42–7.44 (m, 2 H), 7.35–7.37 (m, 2 H), 5.07 (d, J = 11.6 Hz, 2
H), 4.59 (d, J = 11.6 Hz, 2 H), 2.44 (s, 3 H).
13C{1H} NMR (100 MHz, CDCl3):  = 147.7, 143.4, 143.1, 141.1, 128.9,
128.6, 125.3,123.7, 63.4, 21.5.
The product was purified by flash chromatography on silica gel using
90:10 hexanes/EtOAc as the eluent to give a clear colorless oil; yield:
0.676 g (80%).
IR (neat): 1130, 815, 745 cm–1
.
1H NMR (400 MHz, CDCl3):  = 7.64 (d, J = 8.2 Hz, 2 H), 7.33–7.35 (m, 4
H), 7.23–7.25 (m, 2 H), 5.12 (d, J = 12.1 Hz, 1 H), 4.71 (d, J = 12.1 Hz, 1
H), 2.42 (s, 3 H).
13C{1H} NMR (100 MHz, CDCl3):  = 142.9, 141.4, 133.6, 133.4, 130.3,
129.7, 129.6, 129.4, 126.8, 125.2, 63.0, 21.4.
HRMS (ESI): m/z [M + Na]+ calcd for C14H13NO4SNa: 314.0457; found:
314.0453.
The collected spectroscopic data were consistent with the spectro-
scopic data reported in the chemical literature.5
HRMS (ESI): m/z [M + Na]+ calcd for C14H13ClO2SNa: 303.0217; found:
303.0210.
4-Methylbenzyl p-Toluenesulfinate (2c)
The product was purified by flash chromatography on silica gel using
90:10 hexanes/EtOAc as the eluent to give a clear yellow liquid; yield:
0.472 g (90%).
The collected spectroscopic data were consistent with the spectro-
scopic data reported in the chemical literature.5
IR (neat): 1127, 805, 724 cm–1
.
2-Phenylethyl p-Toluenesulfinate (2g)
1H NMR (400 MHz, CDCl3):  = 7.61 (d, J = 8.2 Hz, 2 H), 7.32 (d, J = 8.2
Hz, 2 H), 7.12–717 (m, 4 H), 4.97 (d, J = 11.2 Hz, 1 H), 4.51 (d, J = 11.2
Hz, 1 H), 2.42 (s, 3 H), 2.33 (s, 3 H).
The product was purified by flash chromatography on silica gel using
90:10 hexanes/EtOAc as the eluent to give a clear yellow oil; yield:
0.630 g (81%).
© 2021. Thieme. All rights reserved. Synthesis 2021, 53, A–I

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Synthesis
IR (neat): 1129, 809, 724 cm–1
.
1-Phenyl-1-propyl p-Toluenesulfinate (2k)
1H NMR (400 MHz, CDCl3):  = 7.48 (d, J = 8.2 Hz, 2 H), 7.21–7.29 (m, 5
H), 7.13–7.15 (m, 2 H), 4.22 (dt, J = 7.0, 10.0 Hz, 1 H), 3.81 (dt, J = 7.0,
10.0 Hz, 1 H), 2.92 (td, J = 0.93, 6.9 Hz, 2 H), 2.41 (s, 3 H).
The product was purified by flash chromatography on silica gel using
95:5 hexanes/EtOAc as the eluent to yield a diastereomeric mixture as
a clear colorless oil; yield: 0.4948 g (72%).
IR (neat): 3031, 2971, 1596, 1137, 1037, 753, 699 cm–1
.
13C{1H} NMR (100 MHz, CDCl3):  = 142.6, 141.6, 137.3, 129.6, 128.9,
1H NMR (500 MHz, CDCl3):  (mixture of diastereomers) = 7.44 (d, J =
8.1 Hz, 2 H), 7.38 (d, J = 8.1 Hz, 2 H), 7.26–7.31 (m, 6 H), 7.21 (d, J = 8.1
Hz, 2 H), 7.11–7.12 (m, 3 H), 7.07 (d, J = 8.2 Hz, 2 H), 6.90–7.00 (m, 2
H), 5.08–5.10 (t, J = 6.8 Hz, 1 H), 5.00–5.03 (t, J = 6.8 Hz, 1 H), 2.33 (s, 3
H), 2.28 (s, 3 H), 1.85–1.95 (m, 2 H), 1.73–1.85 (m, 2 H), 0.79 (t, J =
7.41 Hz, 6 H).
128.5, 126.6, 125.2, 64.7, 36.3, 21.5.
HRMS (ESI): m/z [M + Na]+ calcd for C15H16O3SNa: 283.0763; found:
283.0758.
The collected spectroscopic data were consistent with the spectro-
scopic data reported in the chemical literature.5
13C{1H} NMR (125 MHz, CDCl3):  (mixture of diastereomers) = 143.0,
142.5, 142.4, 142.1, 140.6, 140.4, 129.5, 129.2, 128.5, 128.3, 128.0,
127.6, 126.9, 126.6, 125.2, 124.8, 82.8, 80.4, 31.0, 30.8, 21.5, 21.4,
9.96, 9.92.
HRMS (ESI): m/z [M + Na]+ calcd for C16H18O2SNa: 297.0919; found:
297.0918.
3-Benzyloxy-1-propyl p-Toluenesulfinate (2h)
The product was purified by flash chromatography on silica gel using
90:10 hexanes/EtOAc as the eluent to give a clear colorless oil; yield:
0.4755 g (62%).
IR (neat): 2858, 1452, 1130, 1103, 968, 810, 695 cm–1
1H NMR (500 MHz, CDCl3):  = 7.59 (d, J = 8.2 Hz, 2 H), 7.30–7.35 (m, 7
H), 4.49 (s, 2 H), 4.17 (dt, J = 6.2, 10 Hz, 1 H), 3.79 (dt, J = 6.2, 10 Hz, 1
H), 3.55 (td, J = 0.8, 6.2 Hz, 2 H), 2.43 (s, 3 H), 1.92 (q, J = 6.2 Hz, 2 H).
13C{1H} NMR (125 MHz, CDCl3):  = 142.6, 141.9, 138.4, 129.7, 128.3,
127.6, 127.5, 125.2, 72.9, 66.3, 61.7, 30.2, 21.4.
HRMS (ESI): m/z [M + Na]+ calcd for C17H20O3SNa: 327.1025; found:
327.1022.
.
L-Menthyl p-Toluenesulfinate (2l)
The product was purified by flash chromatography on silica gel using
90:10 hexanes/EtOAc as the eluent to give a white solid; yield: 0.505 g
(85%); mp 99–105 °C.
IR (neat): 2947, 2919, 1130 cm–1
.
1H NMR (500 MHz, CDCl3):  (mixture of diastereomers) = 7.60 (d, J =
8.2 Hz, 2 H), 7.32 (d, J = 8.2 Hz, 2 H), 7.26 (s, 1 H), 4.12 (td, J = 10.8,
10.8 Hz, 1 H), 2.25–2.31 (m, 1 H), 2.41 (s, 3 H), 2.05–2.17 (m, 1 H),
1.63–1.71 (m, 2 H), 1.43–1.53 (m, 1 H), 1.31–1.43 (m, 1 H), 1.21–1.30
(m, 2 H), 0.98–1.12 (m, 1 H), 0.96 (d, J = 6.6 Hz, 3 H), 0.86 (d, J = 7.2 Hz,
3 H), 0.72 (d, J = 6.9 Hz, 3 H).
13C {1H} NMR (125 MHz CDCl3,):  (mixture of diastereomers) = 143.3,
143.2, 142.4, 142.3, 129.5, 124. 9, 124.4, 81.9, 80.0, 71.4, 50.1, 48.2,
47.8, 45.0, 43.5, 42.9, 34.5, 34.0, 33.9, 31.8, 31.7, 31.6, 25.8, 23.1, 23.0,
22.1, 22.0, 21.8, 21.5, 21.4, 20.9, 15.4, 15.1.
Diphenylmethyl p-Toluenesulfinate (2i)
The product was purified by flash chromatography on silica gel using
90:10 hexanes/EtOAc as the eluent to give a white solid; yield: 0.5125
g (64%); mp >60 °C (dec.).
IR (neat): 3059, 3029, 1134, 1180, 1079, 811, 738, 700 cm–1
1H NMR (500 MHz, CDCl3):  = 7.44 (d, J = 8.2 Hz, 2 H), 7.24–7.29 (m, 6
H), 7.14–7.16 (m, 4 H), 7.08–7.09 (m, 2 H), 6.26 (s, 1 H), 2.31 (s, 3 H).
.
13C{1H} NMR (125 MHz, CDCl3):  = 142.7, 142.2, 140.3, 140.1, 129.9,
129.4, 128.5, 128.2, 127.8, 127.7, 127.3, 125.1, 80.1, 21.4.
HRMS (ESI): m/z [M + Na]+ calcd for C17H2O2SNa: 317.1546; found:
317.1538.
HRMS (ESI): m/z [M + Na]+ calcd for C20H18O2SNa: 345.0919; found:
The collected spectroscopic data were consistent with the spectro-
scopic data reported in the chemical literature.5
345.0918.
1-Phenylethyl p-Toluenesulfinate (2j)
3-Oxacyclopentyl p-Toluenesulfinate (2m)
The product was purified by flash chromatography on silica gel using
90:10 hexanes/EtOAc as the eluent to yield a 1:1 diastereomeric mix-
ture as a clear colorless oil; yield: 0.5297 g (81%).
The product was purified by flash chromatography on silica gel using
95:5 hexanes/EtOAc as the eluent to give a clear colorless oil; yield:
0.3941 g (70%).
IR (neat): 3030 cm–1
.
IR (neat): 1595, 1135, 1078, 813 cm–1
.
1H NMR (500 MHz, CDCl3):  (mixture of diastereomers) = 7.55 (d, J =
8.2 Hz, 2 H), 7.50 (d, J = 8.2 Hz, 2 H), 7.35–7.37 (m, 2 H), 7.29–7.31 (m,
2 H), 7.20–7.23 (m, 5 H), 7.12–7.14 (m, 2 H), 5.45 (q, J = 6.6 Hz, 1 H),
5.35 (q, J = 6.5 Hz, 1 H), 2.41 (s, 3 H), 2.37 (s, 3 H), 1.65 (d, J = 6.6 Hz, 3
H), 1.56 (d, J = 6.6 Hz, 3 H).
1H NMR (500 MHz, CDCl3):  = 7.58 (d, J = 8.5 Hz, 2 H), 7.33 (d, J = 8.5
Hz, 2 H), 4.90–4.95 (m, 1 H), 3.85–3.95 (m, 2 H), 3.75–3.84 (m, 1 H),
3.64–3.66 (m, 1 H), 2.43 (s, 3 H), 2.16–2.19 (m, 1 H), 1.94–1.98 (m, 1
H).
13C {1H} NMR (125 MHz, CDCl3):  = 143.0, 142.9, 142.0, 129.8, 129.7,
125.1, 125.0, 76.6, 76.1, 73.8, 73.2, 66.8, 34.2, 33.7, 21.4.
HRMS (ESI): m/z [M + Na]+ calcd for C11H14O3SNa: 249.0555; found:
249.0556.
13C{1H} NMR (125 MHz, CDCl3):  (mixture of diastereomers) = 142.8,
142.6, 142.5, 142.1, 141.8, 141.5, 129.6, 129.4, 128.6, 128.3, 128.2,
127.8, 126.4, 126.2, 125.3, 124.9, 75.4, 24.2, 24.0, 21.5, 21.4.
HRMS (ESI): m/z [M + Na]+ calcd for C15H16O2SNa: 283.0763; found:
283.0761.
The collected spectroscopic data were consistent with the spectro-
scopic data reported in the chemical literature.11
The collected spectroscopic data were consistent with the spectro-
scopic data reported in the chemical literature.5
© 2021. Thieme. All rights reserved. Synthesis 2021, 53, A–I

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tert-Butyl p-Toluenesulfinate (2n)
IR (neat): 1505, 1364, 1203, 824 cm–1
.
1H NMR (500 MHz, CDCl3):  = 1.30 (s, 9 H), 2.44 (s, 3 H), 7.04 (m, 2 H),
7.34 (m, 4 H), 7.68 (d, J = 8.2 Hz, 2 H).
13C {1H} NMR (125 MHz, CDCl3):  = 21.5, 31.4, 34.4, 120.8, 125.0,
126.2, 126.5, 129.7, 142.4, 143.3, 148.6, 150.5.
HRMS (ESI): m/z [M + Na]+ calcd for C17H20O2SNa: 311.1076; found:
The p-toluenesulfinic acid (3.75 mmol) served as the limiting reac-
tant with the use of excess tert-butyl alcohol (5 equiv). The product
was purified by flash chromatography on silica gel using 95:5 hex-
anes/EtOAc as the eluent to give a clear colorless oil; yield: 0.606 g
(76%).
IR (neat): 1596, 1125, 852, 782, 718 cm–1
.
311.1075;
1H NMR (500 MHz, CDCl3):  = 7.48 (d, J = 7.9 Hz, 2 H), 7.18 (d, J = 7.9
Hz, 2 H), 2.33, (s, 3 H), 1.47 (s, 9 H).
13C{1H} NMR (125 MHz, CDCl3):  = 143.8, 141.7, 129.4, 124.7, 82.1,
29.7, 21.2.
HRMS (ESI): m/z [M + Na]+ calcd for C11H16O2SNa: 235.0763; found:
235.0763.
p-Methoxyphenoxy p-Toluenesulfinate (25d)
Crude product was isolated to give a yellow wax; yield: 0.72 g (89% as
determined by analytical data).
IR (neat): 1511, 1235, 831 cm–1
.
1H NMR (500 MHz, CDCl3):  = 7.65 (d, J = 8.3 Hz, 2 H), 7.35 (d, J = 8.3
Hz, 2 H), 7.00 (d, J = 9.2 Hz, 2 H), 6.81 (d, J = 9.2 Hz, 2 H), 3.78 (s, 3 H),
2.34 (s, 3 H).
Benzophenone Imine of L-Phenylalaninol (21a)
To a 1000 mL flame dried, N2 purged round-bottomed flask were add-
ed anhyd CH2Cl2 (250 mL), benzophenone imine (11.7 mL, 69.4
mmol), and L-phenylalaninol (10.0 g, 66.1 mmol), and the reaction
mixture was stirred for 24 h at rt. The organic layer was washed with
brine (20 mL), dried (MgSO4), filtered under gravity, and the solvent
was removed by rotary evaporation. The target compound was isolat-
ed as a yellow solid, which was recrystallized from EtOAc (30 mL) and
hexane (2 mL). The yellow crystals were recovered by vacuum filtra-
tion and hexane-wash and air-dried at rt. First and second seeds were
obtained, which yielded a total amount of 20.1 g (97%) of the title
compound as cream-colored crystals; mp 121–124 °C.
13C {1H} NMR (125 MHz, CDCl3):  = 157.5, 145.6, 143.4, 142.1, 126.7,
125.0, 123.1, 114.5, 55.6, 21.6.
HRMS (ESI): m/z [M + Na]+ calcd for C14H14O3SNa: 285.0555; found:
285.0557.
2-Isopropyl-5-methylphenoxy p-Toluenesulfinate (25e)
The crude product was directly isolated as a clear colorless oil; yield:
0.739 g (84% as determined by analytical data).
IR (neat): 2963, 1503, 1237, 939, 812 cm–1
.
1H NMR (500 MHz, CDCl3):  = 7.75 (d, J = 8.2 Hz, 2 H), 7.39 (d, J = 8.2
Hz, 2 H), 7.17 (d, J = 7.9 Hz, 1 H), 7.11 (s, 1 H), 7.00 (d, J = 7.9 Hz, 1 H),
3.17–3.25 (m, 1 H), 2.45 (s, 3 H), 2.33 (s, 3 H), 1.17 (d, J = 7.1 Hz, 3 H),
1.14 (d, J = 7.1 Hz, 3 H).
13C {1H} NMR (125 MHz, CDCl3):  = 150.8, 143.4, 143.0, 137.7, 136.9,
129.8, 126.5, 124.8, 121.8, 26.6, 23.4, 22.9, 21.6, 20.9.
IR (CHCl3 film): 3232, 1620, 1294, 732, 700 cm–1
.
1H NMR (500 MHz, CDCl3):  = 7.55–7.62 (m, 2 H), 7.26–7.39 (m, 6 H),
7.12–7.20 (m, 3 H), 6.94–6.96 (m, 2 H), 6.64 (d, J = 7.1 Hz, 2 H), 3.77–
3.91 (m, 1 H), 3.66–3.71 (m, 2 H), 2.84 (dq, J = 5.4, 7.8 Hz, 2 H), 2.13 (s,
1 H).
13C {1H} NMR (125 MHz, CDCl3):  = 169.8, 144.6, 139.7, 138.9, 138.6,
136.7, 130.1, 129.8, 128.9, 128.6, 128.3, 128.2, 128.1, 127.8, 127.6,
127.4, 126.5, 126.3, 126.0, 125.8, 100.0, 70.5, 66.2, 65.5, 59.6, 39.8,
39.1.
HRMS (ESI): m/z [M + Na]+ calcd for C17H20O2SNa: 311.1076; found:
311.1076.
ESI-HRMS: m/z [M + Na]+ calcd for C23H28N2O3Na: 338.1515; found:
338.1505.
Conflict of Interest
The authors declare no conflict of interest.
2-Diphenylimino-3-phenylpropyl p-Toluenesulfinate (22)
The product was purified by flash chromatography on silica gel using
90:10 hexanes/EtOAc as the eluent to afford a clear colorless oil; yield:
0.8531 g (64%).
Funding Information
Acknowledgment is made to the National Science Foundation (NSF)
for SC-XRD (CHE-1039689) analyses from Departmental instrumen-
tation obtained from the Major Research Instrumentation (MRI) pro-
IR (neat): 2921, 1624, 1445, 949, 694 cm–1
.
1H NMR (400 MHz, CDCl3):  = 7.55 (d, J = 6.8 Hz, 2 H), 7.47 (d, J = 8.1
Hz, 2 H), 7.37–7.38 (m, 1 H), 7.32–7.34 (m, 2 H), 7.29–7.31 (m, 1 H),
7.15–7.22 (br m, 7 H), 6.92–6.94 (m, 2 H), 6.41 (d, J = 7.1 Hz, 2 H),
4.21–4.25 (m, 1 H), 3.88 (dd, J = 4.5, 5.3 Hz, 1 H), 3.70–3.76 (m, 1 H),
2.80 (dd, J = 2.4, 5.6 Hz, 2 H), 2.38 (s, 3 H).
gram.Natio
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Acknowledgment
13C {1H} NMR (100 MHz, CDCl3):  = 169.5, 142.5, 142.0, 139.7, 138.1,
136.5, 130.0, 129.7, 129.5, 128.5, 128.1, 128.0, 127.9, 127.6, 126.1,
125.1, 68.9, 63.5, 39.3, 21.5.
The authors thank the Department of Chemistry of Illinois State Uni-
versity for graduate support for Jessica Shaw (Kurz fellowship) and
Brad J. Austermuehle (Kurz fellowship).
HRMS (ESI): m/z [M + Na]+ calcd for C29H27NO2SNa: 476.1655; found:
476.1642.
Supporting Information
p-tert-Butylphenoxy p-Toluenesulfinate (25c)
Supporting information for this article is available online at
https://doi.org/10.1055/a-1472-7578. 1H and 13C NMR spectroscopic
The crude product was directly isolated as a clear colorless oil; yield:
0.753 g (87%).
data, and X-ray crystallographic data for 21a, are included.
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