Bifunctionalized Allenes. Part XII. Electrophilic Cyclization and Addition Reactions of 4-Sulfinylated or 4-Sulfonylated Allenecarboxylates

Article abstract of DOI:10.1080/10426507.2014.883622

Reaction of 4-sulfinylated or 4-sulfonylated allenecarboxylates with different electrophilic reagents such as sulfuryl chloride, bromine, benzenesulfenyl, and benzeneselenenyl chlorides takes place with 5-endo-trig cyclization or 3,2-addition reaction depending on the kind of the substituent at the sulfur atom. Treatment of 4-(benzenesulfinyl)-allenoates with electrophiles gives 5-(benzenesulfinyl)-2,5-dihydrofuran-2-ones as a result of the neighboring carboxylate group participation in the cyclization. On the other hand, (3E)-4-(methansulfonyl)alk-3-enoates were prepared by chemo-, regio-, and stereoselective electrophilic addition to the C²-C³-double bond in the allenoate moiety of 4-(methanesulfonyl)allenecarboxylates. When R¹ = Me, the treatment with electrophiles gives mixtures of (3E)-4-(methanesulfonyl)alk-3-enoates and (3E)-4-(methanesulfonyl)-2-methylenealk-3-enoates with ratios of about 1.6:1 as a result of addition and elimination reactions. A possible mechanism involving cyclization, addition, and elimination reactions of the 4-sulfinylated or 4-sulfonylated allenecarboxylates is proposed.

Full text of DOI:10.1080/10426507.2014.883622

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Bifunctionalized Allenes. Part XII.
Electrophilic Cyclization and Addition
Reactions of 4-Sulfinylated or 4-
Sulfonylated Allenecarboxylates
Ivaylo K. Ivanova, Ivaylo D. Parusheva & Valerij Ch. Christova
a Department of Organic Chemistry & Technology, Faculty of
Natural Sciences, Konstantin Preslavsky University of Shumen, 115,
Universitetska str. BG-9712, Shumen, Bulgaria
Accepted author version posted online: 30 Apr 2014.Published
online: 26 Aug 2014.
To cite this article: Ivaylo K. Ivanov, Ivaylo D. Parushev & Valerij Ch. Christov (2014): Bifunctionalized
Allenes. Part XII. Electrophilic Cyclization and Addition Reactions of 4-Sulfinylated or 4-
Sulfonylated Allenecarboxylates, Phosphorus, Sulfur, and Silicon and the Related Elements, DOI:
10.1080/10426507.2014.883622
To link to this article: http://dx.doi.org/10.1080/10426507.2014.883622
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Phosphorus, Sulfur, and Silicon, 189:1–11, 2014
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2014.883622
BIFUNCTIONALIZED ALLENES. PART XII. ELECTROPHILIC
CYCLIZATION AND ADDITION REACTIONS OF
4-SULFINYLATED OR 4-SULFONYLATED
ALLENECARBOXYLATES
Ivaylo K. Ivanov, Ivaylo D. Parushev, and Valerij Ch. Christov
Department of Organic Chemistry & Technology, Faculty of Natural Sciences,
Konstantin Preslavsky University of Shumen, 115, Universitetska str. BG-9712,
Shumen, Bulgaria
GRAPHICAL ABSTRACT
E
R1
R1
R
S
E
R
E-Nu
O
R1
•
R
S
or
Y
(On)S
OR2
O
Ph
Me
O
O
CO2R2
O
O
Nu
O
Y = Me, Ph
n = 0 or 1
E = Cl, Br, PhS, PhSe
Nu = Cl, Br
Abstract Reaction of 4-sulfinylated or 4-sulfonylated allenecarboxylates with different elec-
trophilic reagents such as sulfuryl chloride, bromine, benzenesulfenyl, and benzeneselenenyl
chlorides takes place with 5-endo-trig cyclization or 3,2-addition reaction depending on the
kind of the substituent at the sulfur atom. Treatment of 4-(benzenesulfinyl)-allenoates with elec-
trophiles gives 5-(benzenesulfinyl)-2,5-dihydrofuran-2-ones as a result of the neighboring car-
boxylate group participation in the cyclization. On the other hand, (3E)-4-(methansulfonyl)alk-
3-enoates were prepared by chemo-, regio-, and stereoselective electrophilic addition to the
C2 C3-double bond in the allenoate moiety of 4-(methanesulfonyl)allenecarboxylates. When
R1 = Me, the treatment with electrophiles gives mixtures of (3E)-4-(methanesulfonyl)alk-3-
enoates and (3E)-4-(methanesulfonyl)-2-methylenealk-3-enoates with ratios of about 1.6:1 as
a result of addition and elimination reactions. A possible mechanism involving cyclization,
addition, and elimination reactions of the 4-sulfinylated or 4-sulfonylated allenecarboxylates
is proposed.
Keywords 4-Sulfinylated allenoates; 4-sulfonylated allenoates; 2,5-dihydrofuran-2-ones;
neighboring group participation; (3E)-3,2-adducts
Received 23 October 2013; accepted 30 November 2013.
This paper is dedicated to Professor Marko Kirilov from Sofia University, Bulgaria on the occasion of his
90th anniversary and to Professor Toru Minami from Kyushu Institute of Technology, Kitakyushu, Japan on the
occasion of his 75th anniversary.
Address correspondence to Prof. Valerij Ch. Christov, Department of Organic Chemistry & Technology,
Faculty of Natural Sciences, Konstantin Preslavsky University of Shumen, 115, Universitetska str., BG-9712,
Shumen, Bulgaria. E-mail: vchristo@shu-bg.net
1

2
I. K. IVANOV ET AL.
INTRODUCTION
Functionalized allenes have attracted a growing attention because of their versatility
as key building blocks for organic synthesis.1 The synthetic potential of the functionalized
allenes has been explored extensively in recent years, and this has led to the development
of novel methods for the construction of a variety of functionalized heterocyclic and
carbocyclic systems.2 An impressive number of heterocyclic systems has been prepared
from allenic starting materials.
2,5-Dihydrofuran-2-ones (γ -lactones) are important intermediates in organic synthe-
sis due to the presence of the conjugated C C bond as well as the five-membered lactone
ring. Much attention has been paid to the development of efficient and diverse synthetic
methods for construction of this five-membered ring system.3 Among these, cyclization
involving allenecarboxylic acids and their derivatives, the so-called lactonization reaction,
is one of the most efficient pathways.4 α-Allenecarboxylic acids and their esters, disub-
stituted at the γ -carbon atom, underwent electrophilic attack at the central atom and ring
closure to 2,5-dihydrofuran-2-ones (γ -lactones) when treated with electrophile.4
On the other hand, the reactions of allenyl sulfoxides, allenesulfinates, allenyl, and
diallenyl sulfones with electrophilic reagents have been investigated in the 1980s. It has
been shown5 that depending on the structure of the starting allenic compounds, the reac-
tions proceed with ring closure to give 5H-1,2-oxathiol-2-ium salts5a or 5H-1,2-oxathiole
2-oxides (γ -sultines).5b–d Recently, it was also observed by Ma and coworkers that the
electrophilic chlorohydroxylation,6 bromohydroxylation,6 iodohydroxylation,7 oxidative
hydroacetoxylation,8 and selenohydroxylation9 reactions of allenyl sulfoxides with corre-
sponding electrophiles afford E-2,3-adducts with high regio- and stereoselectivity, which
the authors6,7c believed to be determined by the intramolecular attack of the sulfoxide
oxygen at the allenic C3-atom gave the five-membered intermediate.
As a part of our long-standing studies directed toward the development of efficient
electrophilic cyclization reactions of 1,1-bifunctionalized allenes,10 we became interested
in 1,3-bifunctionalized allenes comprising a sulfoxide or sulfone and an ester groups such
as I (Scheme 1). Of particular interest are the applications of these groups as tempo-
rary transformers of chemical reactivity of the allenic system in the eventual synthesis
of heterocyclic compounds. This molecule can be considered as a combination of an
allenyl sulfoxide or an allenyl sulfone and allenecarboxylates and might have different
reactivity profiles in electrophilic reactions. Recently, we presented a convenient and effi-
cient method for regioselective synthesis of 4-sulfinylated or 4-sulfonylated allenecarboxy-
lates, derived by an atom economical [2,3]-sigmatropic rearrangement of the intermediate
alkoxycarbonyl-functionalized propargyl sulfenates or sulfinates formed by reaction of the
alkyl 2-hydroxy-alk-3-ynoates with benzenesulfenyl or methanesulfinyl chlorides, respec-
tively, in the presence of a base.10b
RESULTS AND DISCUSSION
It should be pointed out that conceptually there exist two distinct modes of cyclization
of the 4-sulfinylated or 4-sulfonylated 2,3-alkadienoates if the electrophilic atom forms
a new bond with the central carbon of the allenic system, which seems likely.3–9 It is
evidentthat thesepathwaysarecloselyconnectedwiththeintramolecularneighboringgroup
participation of the sulfoxide or sulfone and/or the ester groups as internal nucleophile(s)

ELECTROPHILIC CYCLIZATION AND ADDITION REACTIONS
3
R
R1
•
Y = Me, Ph
Y
(On)S
OR2
n = 0 or 1
O
O
E = Cl, Br, PhS, PhSe
Nu = Cl, Br
I
E-Nu
R
E
R
E
R
O
E
R1
E
R1
R1
CO2R2
R
Y
(On)S
Nu
Y
(On)S
Y
(On)S
R1
CO2R2
O
O
CO2R2
Y
(On)S
O
O
Nu
IV
O
V
II
III
Scheme 1 Probable products of the electrophilic reaction of 4-sulfinylated or 4-sulfonylated allenecarboxylates
I.
in the final step of the cyclization. Besides the 5-endo-trig cyclizations11 to the 5H-1,2-
oxathiol-2-ium salts II or to the 2,5-dihydrofuran-2-ones (butenolides, γ -lactones) III,
electrophilic addition might afford the 3,2-adduct IV and/or the 3,4-adduct V (Scheme 1).
This paper is a part of our general synthetic strategy for the investigation of the scope
and limitations of the electrophilic cyclization reactions of 1,3-bifunctionalized allenes.
Here, we wish to report our recent results of these investigations.
Br
Ph
Ph
Ph
S
Ph
Br2
•
Ph
OEt
solvent
O
Ph
S
O
O
O
O
3db
1d
Scheme 2 Electrophilic cyclization reaction of ethyl 4-(benzenesulfinyl)-2,4-diphenylbuta-2,3-dienoate 1d with
bromine.
We initiated this study with the electrophilic cyclization reaction of ethyl 4-
(benzenesulfinyl)-2,4-diphenylbuta-2,3-dienoate 1d with bromine (Scheme 2). We
established that the reaction occurs with cyclization by neighboring carboxylate group
participation with formation of the 5-(benzenesulfinyl)-4-bromo-3,5-diphenyl-2,5-
dihydrofuran-2-one 3db. We tried to optimize the reaction conditions to get a useful
selectivity and the best yield for the product by studying the equivalents of electrophile,
reaction temperature, time, and solvent effect. Note that when the reaction was conducted
in 1,2-dichloroethane at room temperature, TLC showed that the two reactants still
interacted and the reaction was completed within 10 h with the formation of the desired
product. It is necessary to carry out this reaction under dry argon since the electrophilic
reagents are sensitive to moisture. The desired product 3db was obtained with 44% yield
(see Table 1, entry 1). When the reaction was carried out at reflux, it was complete within
6 h and the yield was considerably lower (31%, entry 2). With 1.5 equiv. of bromine in
dichloroethane and trichloromethane, the yield is higher (entries 3, 4, and 5). Polar solvents
such as THF, ethanol, acetonitrile, and nitromethane gave low yields, even with longer

4
I. K. IVANOV ET AL.
Table 1 Screening of the cyclization reaction of 1d with bromine under different conditions
Entry
Bromine (equiv.)
Solventa
Reaction temp. (◦C)
Reaction time (h)
Yieldb (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
1.0
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.0
1.2
1.5
2.0
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl
CHCl3
THF
EtOH
MeCN
MeNO2
benzene
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
r.t.
reflux
−78
−20
−20
−20
−30
−20
−20
r.t.
10
6
7
7
6
8
6
8
7
8
8
7
7
9
44
31
51
60
52
51
28
49
57
35
56
66
73c
65
r.t.
−20
−20
−20
aReaction was carried out in the appropriate solvent (10 mL + 10 mL); bYields determined by 1H and 13C
NMR analysis; cIsolated yields after chromatographic purification on silica gel.
reaction times (6–8 h) (entries 6, 7, 8, and 9, respectively). Similar yields were obtained in
benzene as a solvent (entries 10). Fortunately, when dichloromethane was used as a solvent
at room temperature or lower for 7–9 h, the yield improved to 73% (entries 11–14). A
temperature of –20◦C turned out to be the best and most convenient: when the temperature
is higher or lower, the yield is worse (compare entries 1, 2, 10, and 11 with entries 3, and
7). When 1.5 equiv. of electrophilic reagent was used, the reaction was higher yielding
(entry 13). We therefore, conducted the remainder of the reactions in dichloromethane
at –20◦C using 1.0 equiv. of the 4-sulfinylated or 4-sulfonylated allenoates 1a-d and 1.5
equiv. of the electrophilic reagent for several hours (see Table 2). The product 3db was
fully characterized by means of NMR (1H, and 13C) and IR spectroscopy.
Having determined the optimized reaction conditions, we explored the scope of the
electrophilic cyclization reaction of the alkyl 4-(benzenesulfinyl)alka-2,3-dienoates 1a-d
(Scheme 3). The obtained results are summarized in Table 2. It should be noted that the
reaction under this set of standard reaction conditions in the favored 5-endo-trig mode
affords the 5-(benzenesulfinyl)-2,5-dihydrofuran-2-ones 3 as a result of the neighboring
Table 2 Synthesis of the 2,5-dihydrofuran-2-ones 3 by electrophilic cyclization of 1a-d
Entry
Allene
R
R1
R2
E
Nu
Time (h)
3, Yielda (%)
1
2
3
4
5
6
7
8
9
1a
1a
1b
1c
1c
1d
1d
1d
1d
Pr
Pr
Pr
Bu
Bu
Ph
Ph
Ph
Ph
Me
Me
Ph
Me
Me
Ph
Ph
Ph
Ph
Et
Et
Me
Et
Et
Et
Et
Et
Et
Cl
SePh
Br
Br
SePh
Cl
Br
SPh
SePh
Cl
Cl
Br
Br
Cl
Cl
Br
Cl
Cl
4
6
6.5
5
6
6
7
11
9
3aa,70
3ad,68
3bb,72
3cb,71
3cd,67
3da,71
3db,73
3dc,68
3dd,66
aIsolated yields after chromatographic purification on silica gel.

ELECTROPHILIC CYCLIZATION AND ADDITION REACTIONS
5
Table 3 Synthesis of the (3E)-alk-3-enoates 4 by electrophilic addition of 2b,d
Entry
Allene
R
R1
R2
E
Nu
Time (h)
4, Yielda (%)
1
2
3
4
5
2b
2b
2d
2d
2d
Bu
Bu
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Me
Me
Et
Et
Et
Br
SePh
Cl
Br
SePh
Br
Cl
Cl
Br
Cl
7
9
6
9.5
13
4bb,68
4bd,64
4da,67
4db,70
4dd,64
aIsolated yields after chromatographic purification on silica gel.
carboxylate group participation in the cyclization with good to excellent yields irrespective
of the nature of the substituents at the allenic system and the ester group. The reaction
scope is wide: R can be propyl, butyl, or phenyl; R1 can be methyl, or phenyl; R2 can be
methyl, or ethyl; and E can be Cl, Br, PhS, and PhSe.
E
R1
R
S
R1
E-Nu
•
R
S
Ph
OR2
CH2Cl2
O
Ph
O
O
O
O
3
1
Scheme 3 Synthesis of the 2,5-dihydrofuran-2-ones 3 by electrophilic cyclization reaction of 1a-d.
To establish the generality of this methodology, the reaction of the alkyl 4-
(methanesulfonyl)allenecarboxylates 2b,d with different electrophilic reagents such as
sulfuryl chloride, bromine, and benzeneselenenyl chloride was examined. To our sur-
prise, when we applied the current standard conditions to the 1,3-bifunctionalized allenes
comprising a sulfone and alkoxycarbonyl groups such as 2 (Scheme 4), instead of the
2,5-dihydrofuran-2-ones 3, the acyclic compounds 4 were isolated with 64%–70% yield
after stirring for several hours at –20◦C and for another hour at room temperature. The
results are summarized in Table 3. Interestingly, this protocol could also be successfully
applied to the electrophilic reaction of the alkyl 4-(methanesulfonyl)allenoates 2b,d, which
afforded the alkyl (3E)-4-(methanesulfonyl)alk-3-enoates 4 with high regio- and stereose-
lectivity, indicating a highly chemoselective addition reaction of electrophilic reagents to
the C2-C3-double bond of the allenоate system.
R1
R
S
E
R
S
E-Nu
O
R1
O
•
OR2
CH2Cl2
Me
Me
O
CO2R2
O
O
Nu
2b,d
4
Scheme 4 Synthesis of the (3E)-alk-3-enoates 4 by electrophilic addition reaction of 2b,d.

6
I. K. IVANOV ET AL.
Table 4 Synthesis of the (3E)-alk-3-enoates 4 and the (3E)-2-methylenealk-3-enoates 5 by electrophilic addition
and elimination reaction of 2a,c
Entry
Allene
R
E
Nu
Time (h)
4, Yielda (%)
5, Yielda (%)
Ratio
1
2
3
4
2a
2a
2c
2c
Bu
Bu
Ph
Ph
Br
SePh
Br
Br
Cl
Br
Cl
6
8
8
4ab,43
4ad,41
4cb,44
4cd,41
5ab,27
5ad,25
5cb,27
5cd,24
1.55:1
1.63:1
1.61:1
1.72:1
SePh
10.5
aIsolated yields after chromatographic purification on silica gel.
On the other hand, when R1 = Me, the treatment of the ethyl 4-(methanesulfonyl)-
2-methyl-allenecarboxylates 1a,c with electrophiles gives mixtures of the ethyl (3E)-4-
(methanesulfonyl)alk-3-enoates 4 and the ethyl (3E)-4-(methanesulfonyl)-2-methylenealk-
3-enoates 5 in ratios of about 1.6:1 as a result of the highly chemo-, regio-, and stereose-
lective addition to the C2-C3-double bond of the allenoate system and further elimination
reaction (Scheme 5, Table 4).
R
S
E
R
E
R
S
Me
E-Nu
O
Me
O
•
+
Me SO2
OEt
CH2Cl2
Me
Me
O
CO2Et
EtO2C
O
O
Nu
2a,c
4
5
Et3N, benzene
-HNu
Scheme 5 Synthesis of the (3E)–alk-3-enoates 4 and the (3E)-2-methylenealk-3-enoates 5 by electrophilic
addition and elimination reaction of 2a,c.
Thus, on the basis of the literature data on the electrophilic addition on allenes,1,2 on
allenеcarboxylates,4 on allenyl sulfoxides, and on sulfones,5–9 and our previous results,10
a rationale for this reaction is depicted in Scheme 6. The initial act is the attack of the
electrophile (Cl+, Br+, S+, or Se+) on the most nucleophilic atom of the allenic system of
π-bonds (C3) with the formation of the cyclic onium (chloronium, bromonium, thiiranium
or seleniranium) ions A after attack at the C3-C4-double bond or the ions B after attack
on the C2-C3-double bond. Subsequently, the ions A are easily transformed into the more
stable five-membered cyclic ions C via the neighboring group participation of the oxygen
atom of the carboxylate functionality (path a). Furthermore, the intermediates C undergo
attack of the external nucleophile at the R2O group and elimination of alkyl halides (R2Nu)
affording the final cyclic product 3.
On the other hand, in the case of ethyl 4-(methanesulfonyl)allenoates 2 (Y = Me,
n = 1) as starting materials, the formation of the ethyl(3E)-4-(methanesulfonyl)alk-3-
enoates 4 can be considered in terms of the assumption for nucleophilic attack on the cyclic
three-membered onium ions B (path b) leading to the formation of the (3E)-3,2-adduct
4. The observed stereoselectivity may be explained by the favorable trans-arrangement of
the electrophile and the sulfone group and anti-attack of the external nucleophile in the
onium ions on the allenoate C2-C3-double bond B. Moreover, when R1 = Me, together
with the nucleophilic attack at the C2-atom of the onium ions B leading to formation of the

ELECTROPHILIC CYCLIZATION AND ADDITION REACTIONS
7
R1
E
R1
E
path a)
R
S
R
OR2
3
Y = Ph, n = 0
Ph
O
R2
O
O
Y
Y
(On)S
R2Nu
O
Nu
Nu
O
A
C
E-Nu
1, 2
R
E
R1 = Me
path b)
O
R1
CO2Et
S
R
E
Me
Y = Me
n = 1
O
Nu
R1
c)
Et3N
4
(On)S
R2 = Et
CO2R2
R
E
O
path c)
b)
Nu
B
Me SO2
R1 = Me
EtO2C
HNu
5
Scheme 6 A rationale for electrophilic cyclization and addition reactions of 4-sulfinylated or 4-sulfonylated
allenecarboxylates 1,2.
(3E)-3,2-adducts 4 (path b), an attack of the nucleophile at the C2-methyl group of the ions
B affords the elimination products 5 (path c) as the ratio between 4 and 5 is about 1.6:1.
A possible explanation of the occurring addition and subsequent elimination reactions
consists in the following. This reaction pathway is probably favorable from an energetic
point of view. If the sulfonyl group acts as an internal nucleophile in the cyclization,
the obtained cyclic compounds should be oxosulfonium salts (like II, Scheme 1) with
a positive-charged sulfur atom6,12 D (Scheme 7), since in this case, the stabilization by
the elimination of methyl halide and formation of stable cyclic products with sulfinate
group is impossible. Another rationale for the formation of the (3E)-3,2-adducts 4 and the
elimination products 5 consists in the intermediate formation of the oxosulfonium salts D
via neighboring group participation of the oxygen atom of the sulfone functionality (path
aꢀ). Subsequent nucleophilic attack at the C5-atom of the oxosulonium ions D leads to
the formation of the (3E)-3,2-adducts 4 (path b’), but the attack of the nucleophile at the
hydrogen of the C5-methyl group (R1) of the ions D affords the elimination products 5
(path cꢀ). Moreover, the reason for the absence of the adducts (like V, Scheme 1) on the
C3-C4-double bond of the allenoate system probably is the stronger destabilization effect of
a sulfonyl group, in comparison with a sulfoxide group, on the corresponding onium ions
A (not shown in Schemes 6 and 7).
1 = Me
path b')
R
4
5
R
E
R
E
path a')
R1
c')
R1
CO2R2
O
Et3N
S
Y
(On)S
Y = Me
n = 1
Me
CO2Et
O
O
a')
path c')
R
2 = Et
b')
Nu
Nu
B
D
R1 = Me
HNu
Scheme 7

8
I. K. IVANOV ET AL.
The above-mentioned explanation should be corroborated or refuted from the re-
sults of the study on the reactions of other 4-functionalized allenecarboxylates with elec-
trophilic reagents and especially their stereochemistry. Further work in this area is being
focused on exploiting and extending the synthetic utility of the 1,3-bifunctionalized allenes
for the preparation of different heterocyclic systems using the electrophilic cyclization
methodology.
CONCLUSION
We have developed a simple and convenient protocol for the reaction of the 4-
sulfinylated or 4-sulfonylated allenecarboxylates with different electrophilic reagents,
which takes place with 5-endo-trig cyclization or 3,2-addition reaction depending on the
kind of the substituent at the sulfur atom. Treatment of the 4-sulfinylallenoates with elec-
trophiles gives 2,5-dihydrofuran-2-ones as a result of the neighboring carboxylate group
participation in the cyclization. On the other hand, (3E)-4-sulfonylalk-3-enoates were pre-
pared by chemo-, regio-, and stereoselective electrophilic addition to the C2-C3-double bond
in the allenoate moiety. Due to the easy availability of starting materials, the convenient
operation and the usefulness of the butenolide products, the reaction may show potentials
and will be useful in organic synthesis. Further studies on the synthetic applications of
this reaction and the physiological activity of selected cyclic and acyclic products are now
under investigation in our laboratory. Furthermore, a continuation of these studies toward
the synthesis and electrophilic cyclization reactions of other bifunctionalized allenes is
currently in progress in our laboratory.
EXPERIMENTAL
General
All new synthesized compounds were purified by column chromatography and char-
acterized on the basis of NMR, IR, and microanalytical data. NMR spectra were recorded on
DRX Bruker Avance-250 (Bruker BioSpin GmbH, Karlsruhe, Germany) (1H at 250.1 MHz,
13C at 62.9 MHz) and Bruker Avance II+600 (Bruker BioSpin GmbH, Karlsruhe, Germany)
(1H at 600.1 MHz, 13C at 150.9 MHz) spectrometers for solutions in CDCl3. Chemical shifts
are in parts ppm downfield from internal TMS (1H and 13C). J values are given in Hz. IR
spectra (neat, cm−1) were recorded with an FT-IRAfinity-1 Shimadzu spectrophotometer
(Shimadzu Corp., Japan). Elemental analyses were carried out by the Microanalytical Ser-
vice Laboratory of Faculty of Chemistry and Pharmacy, University of Sofia using Vario
EL3 (Elementar Analysensysteme GmbH, Hanau, Germany). Column chromatography was
performed on Kieselgel F25460 (70–230 mesh ASTM, 0.063–0.200 nm, Merck). The melt-
ing points were measured in open capillary tubes and are uncorrected. The solvents were
purified by standard methods. Reactions were carried out in oven-dried glassware under an
Ar atmosphere and exclusion of moisture. All compounds were checked for purity on TLC
plates Kieselgel F25460, Merck.
General Procedure for the Reactions of 4-Sulfinyl- or 4-Sulfonylallene-
carboxylates with Electrophilic Reagents
To a solution of 4-sulfinyl- or 4-sulfonyl-2,3-alkadienoates 1 or 2 (3 mmol) in dry
CH2Cl2 (10 mL) at –20◦C was added dropwise with stirring a solution of the electrophilic

ELECTROPHILIC CYCLIZATION AND ADDITION REACTIONS
9
reagent (sulfuryl chloride, bromine, benzenesulfenyl chloride, benzeneselenenyl chloride)
(4.5 mmol) in the same solvent (10 mL). The reaction mixture was stirred at the same
temperature for several hours (see Tables 2 and 3) and 1 h at room temperature. The
solvent was removed using a rotatory evaporator and the residue was purified by column
chromatography on silica gel (Kieselgel Merck 60 F254) with ethyl acetate/hexane. The
pure 5-(benzenesulfinyl)-2,5-dihydrofuran-2-ones 3 exhibit the following properties:
5-(Benzenesulfinyl)-4-chloro-3-methyl-5-propyl-2,5-dihydrofuran-2-one (3aa).
Light orange oil, yield: 0.63 g (2.10 mmol, 70%). TLC:EtOAc-hexane = 1:1, Rf = 0.75;
IR: 1048 (S O), 1120 (C O C), 1440, 1485 (Ph), 1617 (C C), 1751 (C O). 1H NMR
(600.1 MHz): 0.97 (t, J = 7.4 Hz, 3H, Me (CH2)2), 1.28 (m, 2H, Me CH2 CH2),
1.97 (s, 3H, Me), 2.21 (m, 2H, Me CH2 CH2), 7.42–7.57 (m, 5H, Ph). 13C NMR
(150.9 MHz): 13.1 (CH3), 13.3 (CH3), 16.9 (CH2), 34.8 (CH2), 100.9 (C), 126.2 (C), 154.2
(C), 167.9 (C). C14H15O3SCl (298.79). Calcd: C 56.28, H 5.06; found: C 56.36, H 4.99.
5-(Benzenesulfinyl)-4-bromo-3,5-diphenyl-2,5-dihydrofuran-2-one (3db). Light
yellow oil, yield: 0.96 g (2.19 mmol, 73%). TLC:EtOAc-hexane = 1:4, Rf = 0.77; IR:
1
1044 (S O), 1121 (C O C), 1439, 1488 (Ph), 1620 (C C), 1751 (C O). H NMR
(250.1 MHz): 7.20–8.06 (m, 15H, 3Ph). 13C NMR (62.9 MHz): 87.4 (C), 127.8–132.4
(3Ph), 140.9 (C), 143.2 (C), 160.8 (C). C22H15O3SBr (439.32). Calcd: C 60.15, H 3.44;
found: C 60.09, H 3.50.
The pure alkyl (3E)-4-methanesulfonyl-alk-3-enoates 4 had the following properties:
Ethyl (3E)-2,3-dibromo-4-(methanesulfonyl)-2-methyloct-3-enoate (4ab). Or-
ange oil, yield: 0.54 g (1.29 mmol, 43%). TLC:EtOAc-hexane = 1:4, Rf = 0.78; IR: 1149,
1318 (SO2), 1594 (C C), 1724 (C O). 1H NMR (600.1 MHz): 0.99 (t, J = 7.1 Hz, 3H,
Me (CH2)3), 1.36 (t, J = 7.3 Hz, 3H, Me CH2O), 1.48 (m, 4H, Me (CH2)2 CH2),
1.67 (m, 2H, Me (CH2)2 CH2), 2.00 (s, 3H, Me), 3.03 (s, 3H, MeSO2), 4.28 (m, 2H,
Me CH2O). 13C NMR (150.9 MHz): 14.0 (CH3), 14.7 (CH3), 21.4 (CH2), 28.2 (CH2),
32.7 (CH2), 36.0 (CH3), 42.4 (CH3), 61.3 (CH2), 67.1 (C), 125.7 (C), 148.1 (C), 166.5
(C). C12H20O4SBr2 (420.16). Calcd: C 34.30, H 4.80; found: C 34.36, H 4.73.
Ethyl (3E)-2,3-dibromo-4-(methanesulfonyl)-2,4-diphenylbut-3-enoate (4db).
Yellow oil, yield: 1.05 g (2.10 mmol, 70%). TLC:EtOAc-hexane = 1:3, Rf = 0.79; IR: 1139,
1
1318 (SO2), 1444, 1489 (Ph), 1589 (C C), 1723 (C O). H NMR (250.1 MHz): 0.95
(t, J = 7.2 Hz, 3H, Me CH2O), 3.13 (s, 3H, MeSO2), 3.99 (m, 2H, Me CH2O),
7.31–7.99 (m, 10H, 2Ph). 13C NMR (62.9 MHz): 14.6 (CH3), 38.4 (CH3), 62.6 (C), 74.0
(C), 125.5–137.5 (2Ph), 126.2 (C), 147.8 (C), 156.4 (C). C19H18O4SBr2 (502.22). Calcd:
C 45.44, H 3.61; found: C 45.35, H 3.68.
The pure ethyl (3E)-4-methanesulfonyl-2-methylene-alk-3-enoates 5 exhibit the fol-
lowing properties:
Ethyl (3E)-3-bromo-4-(methanesulfonyl)-2-methyleneoct-3-enoate (5ab). Light
orange oil, yield: 0.27 g (0.81 mmol, 27%). TLC:EtOAc-hexane = 1:4, Rf = 0.49; IR:
1
1146, 1326 (SO2), 1589–1621 (C C), 1727 (C O). H NMR (600.1 MHz): 0.91 (t, J
= 7.0 Hz, 3H, Me (CH2)3), 1.30 (t, J = 7.1 Hz, 3H, Me CH2O), 1.36–1.51 (m, 4H,
Me (CH2)2 CH2), 2.14 (m, 2H, Me (CH2)2 CH2), 3.30 (s, 3H, MeSO2), 4.21 (m, 2H,
Me CH2O), 6.22 (m, 1H, EtO2CaC C(Ha)(Hb)), 6.31 (m, 1H, EtO2CaC C(Ha)(Hb)).
13C NMR (150.9 MHz): 13.1 (CH3), 14.0 (CH3), 23.2 (CH2), 28.1 (CH2), 32.3 (CH2), 41.4
(CH3), 61.1 (CH2), 124.6 (C), 127.3 (C), 143.5 (C), 144.8 (C), 165.7 (C). C12H19O4SBr
(339.25). Calcd: C 42.48, H 5.65; found: C 42.56, H 5.71.
Ethyl (3E)-3-(benzeneselenenyl)-4-(methanesulfonyl)-2-methylene-4-phenylbut
-3-enoate (5cd). Yellow oil, yield: 0.31 g (0.72 mmol, 24%). TLC:EtOAc-hexane = 1:4, Rf
= 0.46; IR: 1145, 1328 (SO2), 1442, 1492 (Ph), 1583–1616 (C C), 1721 (C O). 1H NMR

10
I. K. IVANOV ET AL.
(600.1 MHz): 1.29 (t, J = 7.1 Hz, 3H, Me CH2O), 3.26 (s, 3H, MeSO2), 4.21 (m, 2H,
Me CH2O), 5.84 (m, 1H, EtO2CaC = C(Ha)(Hb)), 6.20 (m, 1H, EtO2CaC C(Ha)(Hb)),
7.22–8.02 (m, 10H, 2Ph). 13C NMR (150.9 MHz): 14.7 (CH3), 41.4 (CH3), 60.2 (CH2),
117.8 (C), 126.7 (C), 127.4–131.1 (2Ph), 132.3 (C), 142.3 (C), 175.1 (C). C20H20O4SSe
(435.40). Calcd: C 55.17, H 4.63; found: C 55.25, H 4.69.
General Procedure for the Preparation of Ethyl
(3E)-4-(methanesulfonyl)-2-methylenealk-3-enoates 5
To a stirred solution of the ethyl (3E)-4-(methanesulfonyl)-2-methylalk-3-enoates
4ad or 4cb (1 mmol) in dry benzene (5 mL) at 8–10 ◦C was added dropwise with stirring, a
solution of NEt3 (1.5 mmol) in the same solvent (5 mL). The reaction mixture was stirred
at the same temperature for 20 min, was refluxed for 2 h and after cooling was quenched
with 2N HCl, extracted with EtOAc, washed with saturated NaCl, and dried over anhydrous
Na2SO4. After evaporation of the solvent, the residue was chromatographed on a column
(silica gel, Kieselgel Merck 60 F254) using a mixture of EtOAc and hexane as eluent to
give the pure ethyl (3E)-4-(methanesulfonyl)-2-methylenealk-3-enoates 5ad (73% yield)
and 5cb (71% yield).
ACKNOWLEDGMENTS
Special thanks to Ismail Ismailov, M.Sc., for the technical help in the synthetic
experiments and chromatographic separations.
FUNDING
The authors gratefully acknowledge the financial support by the Research Fund of the
Konstantin Preslavsky University of Shumen (Project No. RD-08-243/2013), the National
Research Fund of Bulgaria (Project No. DRNF-02-13/2009), and the Human Resources
Development Operational Programme of the European Union (Project No. BG051PO001-
3.3.06-0003/2012).
SUPPLEMENTAL MATERIALS
Supplementary data for this article can be accessed on the publisher’s website,
www.tandfonline.com/gpss
Method of analysis, starting materials, and full spectroscopic and characterization
data including 1H and 13C NMR, IR data, and elemental analyses for all new compounds
as well as literature references to these data for known compounds are listed.
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