Addition reactions of benzenesulfinic acid with glycals and 1,2-dibromosugars

Article abstract of DOI:10.1080/07328300802374805

The addition of benzenesulfinic acid to glycals was investigated under various conditions, and optimized yields of the glycosyl phenylsulfone products were obtained in the presence of tin tetrachloride as a catalyst. Double bond shift (Ferrier rearrangement) occurred in all cases except amicetal, which lacks a substituent at the allylic carbon. Glycosylation of benzenesulfinic acid with 1,2-dibromides was carried out using silver triflate as the promoter, and gave sulfinate esters as products by reaction at oxygen rather than at sulfur. The sulfinate esters were obtained as mixtures of stereoisomers at the stereogenic sulfur atom. Trapping of the sulfinates with carboxylate nucleophiles was observed during attempted oxidation with MCPBA. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/07328300802374805

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Addition Reactions of Benzenesulfinic
Acid with Glycals and 1,2-Dibromosugars
Vikram Basava a , Broc Flores a , Matthew Giovine a , Thomas Licisyn
a , Katelyn Walck a , Walter Boyko a & Robert Giuliano a
a Department of Chemistry , Villanova University , Villanova, PA,
19085, USA
Published online: 29 Oct 2008.
To cite this article: Vikram Basava , Broc Flores , Matthew Giovine , Thomas Licisyn , Katelyn
Walck , Walter Boyko & Robert Giuliano (2008) Addition Reactions of Benzenesulfinic Acid
with Glycals and 1,2-Dibromosugars, Journal of Carbohydrate Chemistry, 27:7, 389-400, DOI:
10.1080/07328300802374805
To link to this article: http://dx.doi.org/10.1080/07328300802374805
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Journal of Carbohydrate Chemistry, 27:389–400, 2008
ꢀC
Copyright Taylor & Francis Group, LLC
ISSN: 0732-8303 print / 1532-2327 online
DOI: 10.1080/07328300802374805
Addition Reactions of
Benzenesulfinic Acid with
Glycals and
1,2-Dibromosugars
Vikram Basava, Broc Flores, Matthew Giovine, Thomas Licisyn,
Katelyn Walck, Walter Boyko, and Robert Giuliano
Department of Chemistry, Villanova University, Villanova, PA 19085, USA
The addition of benzenesulfinic acid to glycals was investigated under various condi-
tions, and optimized yields of the glycosyl phenylsulfone products were obtained in the
presence of tin tetrachloride as a catalyst. Double bond shift (Ferrier rearrangement)
occurred in all cases except amicetal, which lacks a substituent at the allylic carbon.
Glycosylation of benzenesulfinic acid with 1,2-dibromides was carried out using silver
triflate as the promoter, and gave sulfinate esters as products by reaction at oxygen
rather than at sulfur. The sulfinate esters were obtained as mixtures of stereoisomers
at the stereogenic sulfur atom. Trapping of the sulfinates with carboxylate nucleophiles
was observed during attempted oxidation with MCPBA.
Keywords Benzenesulfinic acid, glycosyl phenylsulfones, carbohydrate sulfinate es-
ters
INTRODUCTION
We have recently developed a new method for the iodosulfonation of alkenes
using benzenesulfinic acid and N-iodosuccinimide.[1] Treatment of the product
iodosulfones with neutral alumina in dichloromethane at rt results in dehy-
droiodination to give the corresponding vinyl sulfones in high yield and pu-
rity (Sch. 1). Carbohydrate-derived sulfones[2] and vinyl sulfones[3] are use-
ful as intermediates in the synthesis of amino[4] and branched-chain[5] sugars,
and as precursors to C-glycosides via α-lithiaton,[6] α-samariation,[7] and the
Ramberg-Backlund reaction.[8] It was of interest to investigate the iodosulfona-
tion of glycals using benzensulfinic acid, in an effort to synthesize carbohydrate
Received January 11, 2008; accepted July 31, 2008.
Address correspondence to Robert Giuliano, Department of Chemistry, Villanova Uni-
versity, 800 Lancaster Avenue, 300D Mendel Science Center, Villanova PA 19085.
389

V. Basava et al.
390
sulfones for application in some of these areas, in particular as precursors to
C-glycosides. In this study, we describe the addition of benzenesulfinic acid to
glycals to give glycosyl phenylsulfones, and also the glycosylation of benzene-
sulfinic acid with sugar dibromides to give sulfinate esters.
Scheme 1. Iodosulfonation-dehydrohalogenation with PhSO2H/NIS/alumina.
RESULTS AND DISCUSSION
Previously, we observed that iodosulfonaton of 3,4-di-O-acetyl-L-rhamal with
benzenesufinic acid and N-iodosuccinimide gave a mixture of glycosyl phenyl-
sulfones 1 with no evidence of iodination. The double bond had shifted to
C2-C3 to give a Ferrier-type rearrangement product.[9] Repeating the ex-
periment with a different iodinating reagent (IDCP) produced the same re-
sult, again with no addition of iodine. The addition of benzenesulfinic acid
to tri-O-acetyl-D-glucal had previously been reported by Ley and coworkers,
with improvement in yields when the reaction was carried out using boron
trifluoride-etherate as a catalyst.[10] We had also observed that simple treat-
ment of a glycal, 3,4-di-O-acetyl-L-rhamnal, with excess benzenesulfinic acid in
dichloromethane gave the mixture of sulfones (3:1 α β) in yields ranging from
54% to 86%. A four- to fivefold excess of benzenesulfinic acid was used in these
reactions.
The use of tin tetrachloride as a catalyst in Ferrier reactions involving the
addition of alcohols to glycals was reported by Horton and coworkers.[11] We de-
cided to attempt the tin-catalyzed addition of benzenesulfinic acid to glycals in
an effort to prepare the glycosyl phenylsulfones more efficiently. Results for the
addition of benzenesulfinic acid to glycals using these conditions are summa-
rized in Scheme 2. The amount of catalyst used was 10 mole percent; however,
excess benzenesulfinic acid (three equivalents) was still required to get high
yields of products. The glycosyl phenylsulfones 1 and 2 were obtained as mix-
tures of anomers. In the case of 3,4,6-tri-O-acetyl-D-galactal, only the α-anomer
3 of the phenylsulfone product was obtained. The products of these reactions
were purified by flash chromatography but the mixtures of anomers were

Addition Reactions of Benzenesulfinic Acid
391
inseparable. The products were stable when stored at 0◦C; however, it was ob-
served that anomerization to give a product mixture enriched in the α-anomer
occurred upon chromatography and also on standing for extended periods.
Scheme 2. SnCl4-Catalyzed Addition of PhSO2H to Glycals.
The addition to of benzenesulfinic acid to 4-O-acetyl-L-amicetal[12] gives
an anomeric mixture of glycosyl phenylsulfones 4, with a preference for
the α-anomer (2:1). When iodosulfonation of this glycal was attempted us-
ing N-iodosuccinimide/benzenesulfinic acid, there was no iodosulfone product
obtained.
We were somewhat surprised to observe the absence of products of iodosul-
fonation in the reactions of glycals with PhSO2H/NIS. Evidently, protonation
of the nucleophilic double bond in the vinyl ether moiety is more rapid than
iodonium transfer, unlike the cases of the simple alkenes that were used as

V. Basava et al.
392
substrates in our previous studies of iodosulfonation. When alternate sources
of benzenesulfinate, such as tetra-n-butylammonium benzenesulfinate,[13]
were used in place of benzensulfinic acid in an attempted iodosulfonation of
3,4-di-O-acetyl-L-rhamal, no significant reaction took place. Glycosyl phenyl-
sulfones have been used in several approaches to C-glycosides. Since those
obtained here are allylic, it is expected that they will be suitable substrates
for activation and coupling to aldehydes or other electrophilic reagents.
The reaction of benzenesulfinic acid with sugar dibromides was also in-
vestigated in this study. The direct glycosylation of benzenesulfinic acid with
donors other than glycals has not been reported. Our experience with the addi-
tion reactions of benzenesulfinic acid to glycals had suggested to us that as an
acceptor, benzenesulfinate might be relatively unreactive in the glycosylation
reaction. In addition, benzenesulfinate anion is an ambident nucleophile and
it is known to react with alkylating agents at either sulfur or oxygen to give
sulfones or sulfinate esters, respectively.[14] The nature of the alkylating agent
and solvent appear to be involved in determining the outcome, the latter due
to the extent of hydrogen bonding to the nucleophilic sulfinate ion. Soft elec-
trophiles such as alkyl halides have been shown to favor alkylation at sulfur,
while hard electrophiles such as diazomethane favor the formation of sulfi-
nate esters. For this study, sugar dibromides were selected as donors, since
products of glycosylation at sulfur might be transformed into vinyl sulfones, or
other synthetically useful intermediates.
The glycosylation method we selected for coupling the sugar dibromides
with benzenesulfinic acid in this study was that of Hanessian and Banoub,[15]
in which silver triflate is used as the promoter and tetramethylurea serves
as an acid scavenger. It was considered that silver benzenesulfinate could be
generated in situ under these conditions. Silver salts of benzenesulfinic acid
are known to undergo both S- and O-alkylation,[14] but in the absence of exam-
ples with carbohydrate substrates, we could not predict the preferred mode of
attack of sulfinate on the glycosyl bromide.
The sugar dibromide 3,4,6-tri-O-acetyl-2-bromo-2-deoxy-α-D-mannopyran-
osyl bromide was prepared using tetra-n-butylammonium tribromide, as de-
scribed by Descotes.[16] Crystallization of the product mixture from ether-
hexane gave anomerically pure α-manno dibromide. Results of the coupling
of the dibromide to benzenesulfinic acid in the presence of silver triflate and
tetramethylurea are shown in Scheme 3. The outcome of this experiment was
sensitive to the reaction conditions, in particular the exclusion of air, and the

Addition Reactions of Benzenesulfinic Acid
393
results were difficult to interpret. If the coupling reaction was carried out un-
der an inert atmosphere, a nearly equal mixture of two major sulfinate esters
5 and 6 was obtained, both assigned as α-anomers on the basis of the major
starting dibromide stereochemistry and the small and identical J1,2 of 1.6 Hz.
Sulfur is stereogenic in the sulfinate esters, so mixtures of diastereomers are
obtained. In addition, there were minor amounts of other side-products that
included sulfonate ester 9. Formation of the latter could be suppressed by ex-
clusion of air from the reaction. However, no evidence of sulfone formation that
would result from glycosylation of benzenesulfinic acid at sulfur, rather than
oxygen, was observed. The downfield shifts of the anomeric proton resonances
1
in the H NMR spectra occur at 5.8 to 6.0 ppm, while the alternate, sulfone
products would be expected to exhibit shifts for H-1 at 4.5 to 5.0 ppm.[17]
Scheme 3. Glycosylation of a Sugar Dibromide with Benzenesulfinic Acid.
Glycosyl phenylsulfonate 9 was synthesized from the dibromide 5 by
coupling with benzenesulfonic acid, using the same reaction conditions.
Having 9 in hand helped us to confirm its formation in minor amounts when
the coupling of 5 with benzenesulfinic acid was not conducted under an inert
atmosphere. We also attempted to prepare 9 by oxidation of the sulfinate
esters 6/7 with MCPBA. The only appreciable product isolated from this
experiment was the glycosyl aryl ester 8 (Sch. 4). This raises questions as to
whether oxidation of sulfinate to sulfonate occurs prior to aryl ester formation,
and whether both sulfintate and sulfonate undergo coupling to form the
ester. Treatment of neither the sulfinate esters nor 9 with excess MCBA gave
ester 8. Further experiments would be required to elucidate the details of
the sulfinate esterification, or to demonstrate that sulfinate esters may serve
as glycosyl donors toward other nucleophiles. In the present study, reaction
conditions were developed for the reproducible synthesis of sulfinate esters
from readily available sugar dibromides.

V. Basava et al.
394
Scheme 4. Oxidation/Esterification of Phenylsulfinate Esters.
The α-manno dibromide 10, obtained from 3,4-di-O-acetyl-L-rhamnal by
bromination with tetra-n-butylammonium tribromide, also underwent glyco-
sylation with benzenesulfinic acid to provide bromosulfinate esters 11/12 as a
1:1 mixture of sulfinate diastereomers, both assigned as α-anomers (Sch. 5).
Again, the formation of sulfones was not detected. Also, the formation of sul-
fonate by-products was not observed when the reaction was carried out under
argon. Purification by chromatography and by crystallization were attempted
on the mixtures of sulfinate esters without success.
Scheme 5. Synthesis of Phenylsulfinate Esters from a Rhamnal-Derived Dibromosugar.
Sulfinate esters derived from carbohydrates are not well known and
their chemistry has not been well studied. Benzenesulfinate esters derived
from menthol have previously been synthesized and shown to react with
organometallic reagents to give chiral sulfoxides by Harpp.[18] Applications

Addition Reactions of Benzenesulfinic Acid
395
of sulfinate esters in carbohydrate chemistry are under investigation in our
laboratory.
EXPERIMENTAL
General Procedure for the Addition of Benzenesulfinic Acid to
Glycals
Benzenesulfinic acid was prepared by acidification of the sodium salt with
12M HCl and drying of the product in a vacuum oven (25 mm Hg) at rt
overnight, then stored at 0◦C.1 To a stirring solution of the glycal in anhy-
drous dichloromethane at 0◦C was added benzenesulfinic acid (see individual
examples below for equivalents of PhSO2H). Ten mole percent of tin tetrachlo-
ride (1 M solution in dichloromethane) was added and the reaction was allowed
to warm to rt and monitored by TLC using mixtures of ethyl acetate-hexane
as noted. Reactions were typically completed in 1 to 3 h, after which addi-
tional dichloromethane was added and the mixture washed with 10% aqueous
sodium bicarbonate solution, water, and brine; dried (Na2SO4); and concen-
trated. Products were obtained as oils, which were further purified by flash
chromatography using the solvent mixtures indicated in each example. As-
signments of NMR chemical shifts to the phenyl sulfinate and sulfonate esters
were made with HETCOR analysis.
Phenylsulfonyl 4-O-acetyl-2,3,6-trideoxy-α.β-L-threo-hex-
2-enopyranoside (1)
From 2.14 g (10 mmol) of glycal, treated with benzenesulfinic acid
4.06 g (29 mmol, 2.9 eq) and 1.0 mL tin tetrachloride solution in 60 mL an-
hydrous dichloromethane, there was obtained 2.87 g (97%) of product as a 3:1
αβ anomeric mixture after purification by flash chromatography with 1:4 ethyl
acetate-hexane. Rf 0.4 (40% ethyl acetate-hexanes). The anomers were not sep-
arated. NMR and other analytical data for 1 α have previously been reported
from this laboratory.[1]
Phenylsulfonyl 4,6-di-O-acetyl-2,3-dideoxy-α, β-D-threoo-hex-
2-enopyranoside (2)
From 0.287 g (1.05 mmol) of glycal, treated with benzenesulfinic acid
(0.398 g, 2.8 mmol) and 0.2 mL tin tetrachloride solution in 6 mL
dichloromethane, there was obtained 0.34 g (89%) of product as a 3:1 α β
anomeric mixture after purification by flash chromatography with 1:2 ethyl
1
acetate-hexane. The anomers were not separated. Rf 0.5. The H NMR for 2α
matched that reported.[10]

V. Basava et al.
396
Phenylsulfonyl 4,6-di-O-acetyl-2,3-dideoxy-αD-erythro-hex-
2-enopyranoside (3)
From 0.289 g (1.06 mmol) of glycal, treated with benzenesulfinic acid (0.457
g, 3.2 mmol) and 0.2 mL tin tetrachloride solution in 6 mL dichloromethane,
there was obtained 0.317 g (85%) of product as a white solid after purifica-
tion by flash chromatography with 1:3 ethyl acetate-hexane: mp 148–150◦C.
Rf 0.48. [α]2D3 –61.1◦ (c, 1.8, methanol). 1H NMR (300 MHz, CDCl3): α 8.00 (m,
2H, Ph-H), 7.72 (m, 1H, Ph-H), 7.59 (m, 2H, Ph-H), 6.56 (m, 1H, J3,4 5.6 Hz,
H-3), 6.49 (dd, 1H, J2,3 10.3 Hz, H-2), 5.21 (dd, 1H, J1,2 2,9 Hz, J1,3 2.0 Hz,
H-1), 5.14 (dd, 1H, J4,5 2.4 Hz, H-4), 4.91 (m, 1H, J5,6 6.1 Hz, H-5), 4.14 (m,
2H, H-6), 2.14 (s, 3H, CH3), 2.05 (s, 3H, CH3). 13C NMR α 170.5, 170.2, 137.1,
134.5, 129.5, 129.4, 128.3, 122.9, 88.6, 70.8, 63.3, 62.4, 21.2, 21.0. HRMS calcd
for C16H18O7NaS (M + Na)+: 377.0671. Found: 377.0673.
Phenylsulfonyl 4-O-acetyl-2,3,6-trideoxy-α, β-L-threo-
hexopyranoside (4)
To a solution of 4-O-acetyl-6-deoxy-L-amicetal (39 mg, 0.25 mmol) in
anhydrous dichloromethane (3 mL) was added benzenesulfinic acid (213 mg,
1.5 mmol) and the mixture was stirred at 0◦C initially then overnight at rt.
The reaction was diluted with excess dichloromethane (40 mL); washed with
10% NaHSO3 (40 mL), water (40 mL), and brine (40 mL); dried over anhy-
drous Na2SO4; and concentrated. The crude product was then purified by flash
chromatography over silica gel by the gradient elution method using 40% to
50% ethyl acetate. The product 4 (55 mg, 74%), a 2:1 mixture of β/α anomers,
is obtained as a colorless oil. Rf0.44 (40% ethyl acetate/hexanes). 1H NMR
(α-anomer) β, α7.92 (m, 2H, Ph-H); 7.69 (m, 1H, P-H), 7.57 (m, 2H, Ph-H),
4.38 (dd, 1H, J1,2e 2.1 Hz, J1,2a 11.8 Hz, H-1), 3.43 (m, 1H, J4,5 9.6 Hz, J5,6 6.2
Hz H-5), 2.02 (s, 3H, CH3), 1.16 (d, 3H, CH3). Analytical MW calculated for
C14H18O5S is 298.08. Found by ESI MS (M + NH4)+ 314.3 (38%), 155.3 (100%).
Phenylsulfinyl 3,4,6-tri-O-acetyl-2-bromo-2-deoxy-α-
D-mannopyranosides (6/7)
To a stirring solution of tri-O-acetyl-D-glucal (0.27 g, 1 mmol) in ethyl
acetate (6 mL) under argon was added tetra-n-butylammonium tribromide
(0.485 g, 1 mmol) and the yellow solution was stirred under argon at rt for
1.5 h. Ethyl acetate (5 mL) was added and the reaction was filtered through
Celite and the filtrate washed with water (2 × 5 mL) and sat’d aqueous sodium
chloride, dried (Na2SO4), and concentrated to a syrup, which was composed
of a 9:1 mixture of α-manno/α-gluco 1,2-dibromides, Rf = 0.52 (40:60 ethyl
acetate/hexanes). Crystallization from ether-hexane gave anomerically pure

Addition Reactions of Benzenesulfinic Acid
397
1H NMR of 6/7 (300 MHz, CDCl3):
13C NMR of 6/7 (70.4 MHz CDCl3):
Assignment
1
2
3
4
5
6a
6b
6
5.979
4.454
5.195
5.445
3.988
4.097
3.689
2.085,
2 × 2.033
7
Assignment
1
2
3
4
5
6
6
7
5.840
4.362
5.121
5.435
4.058
4.245
4.150
2.135,
2.082,
2.066
∼7.77
∼7.60
∼7.60
95.40
48.60
68.36
65.47
70.50
61.05
ND
96.95
48.60
68.09
65.20
70.24
61.71
ND
Acetate methyl
Phenyl, i
CH3CO
144.23
143.72
Phenyl, o
Phenyl, m
Phenyl, p
∼7.77
∼7.60
∼7.60b
Phenyl, o
Phenyl, m
Phenyl, p
Acetate carbonyl
124.41
128.96
132.69
ND
124.31
129.15
132.95
ND
JI,K,Hz
1, 2
2, 3
3, 4
4, 5
5, 6a
5, 6b
6a, b
1.6
4.0
9.8
9.7
3.8
2.3
12.5
1.6
4.0
9.8
10.0
4.9
2.5
12.5
α-manno dibromide; yield, 0.307 g (71%). The 1H NMR data matched that
reported.[16] A sample of the dibromide (0.307 g, 0.71 mmol) was taken up in
˚
dry dichloromethane (12 mL) and 4 A molecular sieves (0.20 g) were added,
followed by (at 0◦C under argon) benzenesulfinic acid (0.607 g, 4.27 mol) and
TMU (0.248 g, 2.14 mol). After stirring 10 min, silver triflate (0.407 g, 1.58
mmol) was added. The mixture was stirred for 1.5 hr at 0◦C under argon, then
diluted with 15 mL dichloromethane and transferred to a separatory funnel
and washed with sat’d aqueous sodium bicarbonate solution (10 mL). The mix-
ture was washed with water, dried (Na2SO4), and concentrated to an oil (0.199
g). The crude product contained two major components that were assigned as
two diastereomeric α-sulfinates (6/7) in an approximate 1:1 ratio; yield, 57%.
When the reaction was carried out without rigorous maintenance of an inert
argon atmosphere, the formation of sulfonate 9 and other by-products was ob-
served. Sulfinates 6/7 had Rf 0.34 (40% ethyl acetate/hexanes).
HRMS calcd for C18H21O9SBrNa (M + Na)+: 514.9987. Found 515.0015.

V. Basava et al.
398
3,4,6-Tri-O-acetyl-2-bromo-2-deoxy-1-O-m-chlorobenzoyl-a-
D-mannopyranose (8)
To a solution of sulfinate esters 6/7 (0.25 g, 0.5 mmol) in dichloromethane
(5 mL) was added with MCPBA (0.15 g of 77%, 0.65 mmol, 1.3 equiv) over 7 hr
while stirring at rt for 1 h. An additional three portions of MCPBA (0.15 g) were
added over a period of 7 hr and the reaction was stirred at 35◦C. The reaction
was quenched by the addition of aqueous NaOH solution and the organic phase
was separated, washed with 10% aqueous NaI solution (4 mL), dried (Na2SO4),
and concentrated to yield the ester 8 as a white powder (0.13 g, 51%). [α]D23
=
1
−3.9 (c, 1.0, dichloromethane). H NMR (300 MHz, CDCl3): α 8.09, 7.99, 7.59,
7.43, 5.51 (d, 1H, J1,21.6 Hz, H-1), 5.44 (dd, J3,49.6 Hz, J4,5 9.6 Hz, H-4), 5.32
(dd, J2,33.8 Hz, H-3), 4.49 (dd, 1H, H-2), 4.27 (m, 1H, H-5), 4.20 (m, 2H, H-
6), 2.11 (s, 3H, CH3), 2.10, (s, 3H, CH3), 2.07 (s, 3H, CH3). HRMS calcd for
C19H20ClBrO9Na: 528.9877 (M + Na). Found: 528.9891.
Phenylsulfonyl 3,4,6-tri-O-acetyl-2-bromo-2-deoxy-α-
D-mannopyranoside (9)
To a solution of 3,4,6-tri-O-acetyl-2-bromo-2-deoxy-a-D-mannopyranosyl
bromide (0.421 g, 0.9744 mmol), prepared from tri-O-acetyl-D-glucal as de-
scribed above, in dichloromethane (10 mL) at 0◦C under argon were added
˚
4 A molecular sieves (0.2 g) followed by benzenesulfonic acid (0.639 g, 4.04
mmol) and 1,1,3,3-tetramethylurea (0.344 g, 2.96 mmol). The mixture was
stirred 10 min and then silver triflate (0.251 g, 0.97 mmol) was added and stir-
ring was continued for 3 h. The mixture was filtered through a Celite pad, the
solid washed with dichloromethane, and the filtrate washed with sat’d aque-
ous sodium bicarbonate solution and water, dried (Na2SO4), and concentrated
to a yellow oil that contained the sulfonate 9 (0.471 g, 95%) as a mixture of
α- and β-anomers (6:1) that was not purified further. Rf 0.42 (40% ethyl ac-
1
etate/hexanes. H NMR (a-anomer, 300 MHz, CDCl3): α 7.98, 7.60, 7.71, 6.13
(d, 1H, J1,21.5 Hz, H-1), 5.42 (dd,1H, J3,49.8 Hz, J4,5 10.2 Hz, H-4), 5.15 (dd,
1H, J2,34.0 Hz, H-3), 4.50 (dd, 1H, H-2), 3.99 (dd, 1H, J6a,6b12.7 Hz, H-6a), 3.70
(m, 1H, J5,6a3.6 Hz, J5,6b2.4 Hz, H-5), 3.56 (dd, 1H, H-6b), 2.08 (s, 3H, CH3),
2.06, (s, 3H, CH3), 2.07 (s, 3H, CH3).
Phenylsulfinyl 3,4-di-O-acetyl-2-bromo-2,6-di-deoxy-α-
L-mannopyranosides (11/12)
To a solution of crystalline 3,4-di-O-acetyl-2-bromo-2,6-di-deoxy-α-L-
mannopyranosyl bromide 10 (0.226 g, 0.61 mmol), prepared from 3,4-di-O-
acetyl-6-deoxy-L-glucal by bromination with tetra-n-butylammonium tribro-
mide as described16 in anhydrous dichloromethane (10 mL) at 0◦C under
˚
argon, were added 4 A molecular sieves (0.2 g), benzenesulfinic acid (0.449 g,
2.84 mmol), and 1,3,3-tetramethylurea (0.175 g, 1.51 mmol). After stirring for

Addition Reactions of Benzenesulfinic Acid
399
10 min, silver triflate (0.268 g, 1.04 mmol) was added and the reaction was
stirred 2.5 hr at 0◦C. The reaction was diluted with dichloromethane (15 mL),
washed with sat’d sodium bicarbonate solution and water, dried (Na2SO4), and
concentrated to an oil that contained phenylsulfinate esters 11/12 in an ap-
proximate 1:1 ratio; yield, 0.214 g (81%). Rf 0.39 (40% ethyl acetate in hex-
anes). Analytical MW calculated for C16H19O7SBr: 434.99. Found by ESIMS
(M + NH4)+452.2 (100%), 293.2 (22%), 233.2 (13%).
1H NMR of 11/12 (300 MHz, CDCl3): 13C NMR of 11/12 (70.4 MHz CDCl3):
Assignment
11
12
Assignment
11
12
1
2
3
4
5
6
5.90 d
4.45 dd
∼5.14 cm
∼5.14 cm
3.86 dq
0.94 d
5.79 d
4.36 dd
5.06 dd
5.20 t
3.94 dq
1.21 d
1
2
3
4
5
94.94
49.24
68.42
70.38
68.42
96.88
49.19
68.17
70.38
68.71
6
16.82
17.20
CH3CO
Phenyl-o
2.03–2.11 2.03–2.11
7.74–7.78 7.74–7.78
CH3CO
Phenyl-i
Phenyl-o
Phenyl-m
Phenyl-p
CH3CO
20.5–20.7
144.35
124.38
128.85
132.42
20.5–20.7
143.99
124.26
129.09
132.72
Phenyl-m/p 7.52–7.63 7.52–7.63
JI,K, Hz
1, 2
1, 5
2, 3
3, 4
4, 5
5, 6
1.5
0.7
3.5
ND
9.7
6.3
1.7
0.6
3.9
9.7
9.7
6.4
169.2–169.7 169.2–169.7
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