Bifunctionalized allenes. Part VIII. An efficient and varied method for the synthesis of 2-sulfonylated alka-2,3-dienoates

Article abstract of DOI:10.1080/10426507.2012.718299

An efficient and varied method for the synthesis of 2-sulfonylated alka-2,3-dienoates by intermediate formation of allenecarboxylates, allenyl sulfones, and propargyl sulfinates using the relatively high acidity of the hydrogen atom at the allenic C-1 ato

Full text of DOI:10.1080/10426507.2012.718299

This article was downloaded by: [Northeastern University]
On: 28 December 2014, At: 13:53
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered
office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Phosphorus, Sulfur, and Silicon and the
Related Elements
Publication details, including instructions for authors and
subscription information:
http://www.tandfonline.com/loi/gpss20
Bifunctionalized Allenes. Part VIII. An
Efficient and Varied Method for the
Synthesis of 2-Sulfonylated Alka-2,3-
Dienoates
Ivaylo K. Ivanov a & Valerij Ch. Christov a
a Faculty of Natural Sciences, Department of Organic Chemistry and
Technology, Konstantin Preslavsky University of Shumen , Shumen ,
Bulgaria
Accepted author version posted online: 10 Aug 2012.Published
online: 05 Jul 2013.
To cite this article: Ivaylo K. Ivanov & Valerij Ch. Christov (2013) Bifunctionalized Allenes. Part VIII.
An Efficient and Varied Method for the Synthesis of 2-Sulfonylated Alka-2,3-Dienoates, Phosphorus,
Sulfur, and Silicon and the Related Elements, 188:7, 913-919, DOI: 10.1080/10426507.2012.718299
To link to this article: http://dx.doi.org/10.1080/10426507.2012.718299
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the
“Content”) contained in the publications on our platform. However, Taylor & Francis,
our agents, and our licensors make no representations or warranties whatsoever as to
the accuracy, completeness, or suitability for any purpose of the Content. Any opinions
and views expressed in this publication are the opinions and views of the authors,
and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content
should not be relied upon and should be independently verified with primary sources
of information. Taylor and Francis shall not be liable for any losses, actions, claims,
proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or
howsoever caused arising directly or indirectly in connection with, in relation to or arising
out of the use of the Content.
This article may be used for research, teaching, and private study purposes. Any
substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,
systematic supply, or distribution in any form to anyone is expressly forbidden. Terms &

Conditions of access and use can be found at http://www.tandfonline.com/page/terms-
and-conditions

Phosphorus, Sulfur, and Silicon, 188:913–919, 2013
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2012.718299
BIFUNCTIONALIZED ALLENES. PART VIII. AN EFFICIENT
AND VARIED METHOD FOR THE SYNTHESIS OF
2-SULFONYLATED ALKA-2,3-DIENOATES
Ivaylo K. Ivanov and Valerij Ch. Christov
Faculty of Natural Sciences, Department of Organic Chemistry and Technology,
Konstantin Preslavsky University of Shumen, Shumen, Bulgaria
GRAPHICAL ABSTRACT
O
R
R1
R2
R1
R2
R1
R2
S
O
EtO
•
•
HO
O
Abstract An efficient and varied method for the synthesis of 2-sulfonylated alka-2,3-dienoates
by intermediate formation of allenecarboxylates, allenyl sulfones, and propargyl sulfinates
using the relatively high acidity of the hydrogen atom at the allenic C-1 atom and the [2,3]-
sigmatropic rearrangement is described.
Supplemental materials are available for this article. Go to the publisher’s online edition of
Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.
Keywords 2-Sulfonylated alka-2,3-dienoates; allenecarboxylates; allenyl sulfones; synthesis
INTRODUCTION
Allenes are unique compounds in organic chemistry by virtue of their adjacent,
orthogonal π-bonds. Synthesis and use of allene derivatives have been expanded in prepar-
ative organic chemistry in the past three decades. The presence of two π electron clouds
separated by a single sp hybridized carbon atom is the identifying structural characteristic
of allenes, and it is this unique structural and electronic arrangement that is responsible for
the extraordinary reactivity profile displayed by allenic compounds.1
Functionalized allenes have attracted a growing attention because of their versatility
as key building blocks for organic synthesis. Functionalized allenes could be potentially
involved in a number of transformations due to their high reactivity. Their main synthetic
Received 20 June 2012; accepted 1 August 2012.
Support from the Research Fund of the Konstantin Preslavsky University of Shumen (Projects Nos. RD-
05-137/2011 and RD-05-247/2012) is acknowledged. Special thanks to MSc Boris Prodanov and MSc Radost
Nikolova for the technical help in the chromatographical separations.
Address correspondence to Prof. Dr. Valerij Ch. Christov, Faculty of Natural Sciences, Department of
Organic Chemistry and Technology, Konstantin Preslavsky University of Shumen, 115 Universitetska Str., BG-
9712, Shumen, Bulgaria. E-mail: vchristo@shu-bg.net
913

914
I. K. IVANOV AND V. CH. CHRISTOV
application is presently based on their ability to undergo function assisted lithiation and
subsequent reactions with various electrophiles.2–4
Reaction of propargyl alcohols with sulfinyl chlorides is a convenient method for the
preparation of propargyl sulfinates, which usually undergo [2,3]-sigmatropic rearrangement
to allenyl sulfones.5 An alternative route starts from methyl 4-hydroxy-2-alkynoate that
enables the preparation of sulfonyl-substituted6 allenecarboxylates.
As a part of our research program on the chemistry of the bifunctionalized allenes, we
required a convenient method to introduce the sulfonyl group in the α-position to the ester
group of the allenecarboxylates or the ester group in the α-position to the sulfonyl group
of the allenyl sulfones. In continuation of our previous reports on the synthesis7a,7b,7g and
electrophilic cyclization reactions7a–7f of bifunctionalized allenes, we have found an efficient
and varied method for the synthesis of 2-sulfonylated alka-2,3-dienoates by intermediate
formation of allenecarboxylates and allenyl sulfones.
RESULTS AND DISCUSSION
The method for the synthesis of the 2-sulfonylated alka-2,3-dienoates 7 consists
of the following experimental procedures according to the reaction sequence outlined in
Scheme 1.
R1
R2
R1
R2
R1
R2
i)
•
•
Li
HO
1
2
8
iv)
ii)
Procedure A
Procedure B iii)
R1
R2
R1
R2
R1
R2
v)
O
•
•
Procedure C
EtO
EtO
S
O
R
O
O
O
R
S
3
5
O
vi)
Procedure D
viii) Procedure E
9
R1
R2
R1
R2
Li
Li
O
•
•
S
R
O
6
4
vii)
ix)
O
R
S
R1
R2
O
EtO
O
•
7
Scheme 1 An efficient and varied method for synthesis of the 2-sulfonylated alka-2,3-dienoates 7 by intermediate
formation of the allenecarboxylates 3, the allenyl sulfones 5, and the propargyl sulfinates 9.

SYNTHESIS OF 2-SULFONYLATED ALKA-2,3-DIENOATES
915
Table 1 Synthesis of the allenecarboxylates 3, the allenyl sulfones 5, and the 2-sulfonylated allenecarboxylates
7 according to Scheme 1
Yieldsa (%), according to procedure no.
Entry
R
R1
R2
Allene
A
B
Cb
D
E
1
2
3
4
5
6
7
8
9
Me
Me
Me
CCl3
CCl3
Ph
Me
-(CH2)5-
Me
Me
-(CH2)5-
Me
-(CH2)5-
Me
-(CH2)5-
Me
Me
3a, 5a, 7a c
3b, 5b, 7b c
3c, 5c, 7c
3a, 5d, 7d c
3b, 5e, 7e
3a, 5f, 7f
3b, 5g, 7g
3a, 7h
67
65
66
67
65
67
65
67
65
66
69
71
69
70
74
—
70
—
—
—
49
52
—
—
51
49
47
—
—
—
64
64
58
50
—
57
65
60
62
59
70
64
67
61
66
63
61
—
—
—
Ph
Me
Me
Me
Ph
Ph
Me3SiO
Me3SiO
Me3SiO
3b, 7i
3c, 7j
10
aIsolated yields by chromatographical purification on silica gel.
bOverall yields without isolation of the alkynes 9.
cCompounds 7a, 7b, and 7d have been described in our earlier article.7g
Procedure A: Reaction of the lithio compounds 2, in situ generated from alka-
1,2-diene 1 and n-BuLi in tetrahydrofuran (THF) at −60◦C, with ethyl chloroformate
leads to formation of the expected allenecarboxylates 3a–b, that were isolated by column
chromatography as pale yellow oils in 65–67% yield after a conventional workup (see
Table 1).
Reagents and conditions:
i) BuLi, THF, −60◦C, 1 h, −20◦C, 1 h;
ii) Procedure A: ClCO2Et, THF, −60◦C to r.t., 1 h;
iii) Procedure B: RSO2Cl (R = Me, CCl3, Ph), THF, −60◦C to r.t., 2 h;
iv) Procedure C: RS(O)Cl (R = Me, CCl3, Ph), Et3N, ether, −60◦C, 1 h, r.t., 3 h;
v) [2,3]-sigmatropic rearrangement, toluene, reflux, 3 h;
vi) Procedure D: BuLi, THF, −60◦C, 1 h;
vii) RSO2Cl, (R = Me, CCl3, Ph, Me3SiO), THF, −60◦C to r.t., 2 h;
viii) Procedure E: BuLi, THF, −60◦C, 1 h;
ix) ClCO2Et, THF, −60◦C to r.t., 2 h;
Procedure B: The allenyl sulfones 5 are readily available by the reaction of the
lithiated alka-1,2-diene 2, prepared in situ according to Procedure A, with methane-,
trichloromethane-, or benzene-sulfonyl chloride in 69–74% isolated yield by chromato-
graphical purification on silica gel.
Procedure C: Another strategy for the synthesis of the allenyl sulfones 5, using our
experience on the preparation of the vinyl allenyl sulfones,8 relies on the well-precedented
[2,3]-sigmatropic rearrangement of propargylic sulfinates to allenyl sulfones.5 The starting
materials in the synthesis of the allenyl sulfones 5 are the appropriate α-alkynols 8, which
react with methane-, trichloromethane-, or benzene-sulfinyl chloride in the presence of
triethyl amine. Reflux of the intermediate formed propargyl sulfinates 9 (which may be
or not be isolated) in toluene provokes a [2,3]-sigmatropic rearrangement to the expected

916
I. K. IVANOV AND V. CH. CHRISTOV
allenyl sulfones 5, which were purified by column chromatography on silica gel with
47–52% overall yield.
Procedure D: We found that the allenecarboxylates 3a–c, prepared according to
Procedure A, can smoothly be deprotonated at α-position by n-BuLi in THF. The in situ
resulting lithio compounds 4 can react with methane-, trichloromethane-, benzene-, or
trimethylsilyloxy-sulfonyl chloride to give the pure 2-alkane(benzene)sulfonyl-allenoates
7a–g or 2-trimethylsilyloxysulfonyl-allenoates 7h–j in 50–65% yield after column chro-
matographically purification. Compounds 7a, 7b, and 7d have been described in our earlier
article.7g
Procedure E: The synthesized allenyl sulfones 5, according to Procedure
B or Procedure C, undergo in situ lithiation at the α-carbon in treatment with
n-BuLi and subsequent reaction with ethyl chloroformate to produce the desired 2-
alkane(benzene)sulfonyl-allenoates 7a–g, which after a conventional workup were isolated
by column chromatography as light yellow oils in 61–70% yield.
In conclusion, a convenient, efficient, and varied method for the synthesis of a new
family of 1,1-diacceptor-substituted allenes—namely 2-sulfonylated allenecarboxylates,
derived by intermediate formation of allenecarboxylates, allenyl sulfones, and propargyl
sulfinates applying the relatively high acidity of the hydrogen atom at the allenic C-1 atom
and the [2,3]-sigmatropic rearrangement—has been explored. Further investigations on this
potentially important synthetic methodology are currently in progress. At the same time,
the synthetic application of the prepared 2-sulfonyl-functionalized allenecarboxylates for
the synthesis of different heterocyclic compounds is now under investigation as a part of our
general synthetic strategy for investigation of the score and limitations of the electrophilic
cyclization reactions of bifunctionalized allenes. Results of these investigations will be
reported in due course.
EXPERIMENTAL
Synthesis of the Allenecarboxylates 3 According to Procedure A
To a solution of n-BuLi (1.6 M in hexane, 6.25 mL, 10 mmol) in THF (70 mL) was
added, dropwise with stirring over 15 min, a solution of alka-1,2-diene 1 (11 mmol) in
THF (20 mL) at −60◦C. The reaction mixture was stirred at this temperature for 1 h, the
cooling bath was removed and the reaction mixture was allowed to warm up to −20◦C
and stirred at that temperature for 1 h, which was followed by the dropwise addition of a
solution of chloroformate (1.09 g, 10 mmol) in 20 mL of THF at −60◦C. After the addition
was completed, the mixture was warmed to r.t. and stirred for 1 h. Then the mixture
was quenched with 2N HCl, extracted with Et2O, washed with sat. NaCl, and dried over
anhydrous Na2SO4. After evaporation of the solvent, the residue was chromatographed on
column (silica gel, Kieselgel Merck 60 F254) using a mixture of hexane and EtOAc as an
eluent to give the pure allenoates 3a–c.
According to Procedure A, the 1-ethenylidencyclohexane 1b (1.19 g, 11 mmol) was
converted by lithiation with BuLi and following reaction with chloroformate into ethyl
1
3-cyclohexyliden-2-propenoate 3b. Yield: 1.17 g (65%, 6.5 mmol); light yellow oil. H
NMR (CDCl3, 250 MHz): δ = 1.20 (t, J = 7.2 Hz, 3H, MeCH2O), 1.30–2.43 (m, 10H,
cyclohexylidene), 4.04 (q, J = 7.2 Hz, 2H, MeCH2O), 5.37 (s, 1H, =CH). 13C NMR
(CDCl3, 62.9 MHz): δ = 14.8 (CH3), 24.1 (CH2), 26.4 (CH2), 33.0 (CH2), 61.2 (CH2),

SYNTHESIS OF 2-SULFONYLATED ALKA-2,3-DIENOATES
917
90.3 (CH), 102.3 (C), 168.5 (C), 207.6 (C). IR (film): 1712 (C O), 1954 (C C C). Anal.
Calcd. for C11H16O2 (180.24): C, 73.29; H, 8.95. Found: C, 73.35; H, 8.87.
Synthesis of the Allenyl Sulfones 5 According to Procedure B
To lithiated allene 2, generated in situ by Procedure A, was added, dropwise with
stirring, a solution of methane-, trichloromethane-, or benzene-sulfonyl chloride (10 mmol)
in 30 mL of THF at −60◦C. After the addition was completed, the mixture was warmed to
r.t. and stirred for 2 h. Then the mixture was quenched with 2N HCl, extracted with Et2O,
washed with sat. NaCl, and dried over anhydrous Na2SO4. After evaporation of the solvent,
the residue was chromatographed on column (silica gel, Kieselgel Merck 60 F254) using a
mixture of hexane and EtOAc as an eluent to give the pure allenyl sulfones 5a–g.
According to Procedure B, the 3-methylbuta-1,2-diene 1a (0.749 g, 10 mmol) was
converted by lithiation with BuLi and following reaction with trichloromethane-sulfonyl
chloride (2.18 g, 10 mmol) into the 3-methyl-buta-1,2-dienyl trichloromethyl sulfone 5d.
1
Yield: 1.75 g (70%, 7.0 mmol); yellow oil. H NMR (CDCl3, 250 MHz): δ = 1.71 (d,
J = 2.7 Hz, 6H, 2Me), 6.24 (d, J = 2.7 Hz, 1H, =CH). 13C NMR (CDCl3, 62.9 MHz): δ =
21.7 (CH3), 102.8 (C), 106.5 (CH), 107.8 (C), 205.6 (C). IR (film): 1122, 1338 (SO2), 1957
(C C C). Anal. Calcd. for C6H7O2SCl3 (249.53): C, 28.88; H, 2.83; S, 12.85. Found: C,
28.93; H, 2.88; S, 12.91.
Synthesis of the Allenyl Sulfones 5 According to Procedure C
To a solution of α-alkynol 8 (10 mmol) and triethylamine (1.21 g, 12 mmol) in dry
ether (50 mL) at −60◦C was added, dropwise with stirring, a solution of freshly distilled
or recrystallized methane-, trichloromethane-, or benzene-sulfinyl chloride (10 mmol) in
the same solvent (20 mL). The reaction mixture was stirred for 1 h at the same temperature
and for 3 h at r.t. and then washed with water, 2N HCl, extracted with Et2O. The extract
was washed with sat. NaCl, and dried over anhydrous Na2SO4. Evaporation yielded the
crude product 9, which was dissolved in dried toluene (10 mL) and refluxed for 3 h. After
evaporation of the solvent, the crude product was purified by column chromatography
on silica gel (Kieselgel Merck 60 F254) (eluent: EtOAc-heptane) to yield the pure allenyl
sulfones 5a–g.
According to Procedure C, the methyl 3-methyl-buta-1,2-dienyl sulfone 5a (yield:
0.72 g, 49%, 4.9 mmol) was prepared in a one-pot reaction via [2,3]-sigmatropic rearrange-
ment of the 2-methanesulfinyloxy-2-methylbut-3-yn 9a, obtained from 2-methylbut-3-yn-
2-ol 8a (0.84 g, 10 mmol) and methane-sulfinyl chloride (0.99 g, 10 mmol) in the presence
of triethylamine. Spectroscopic properties of 5a were fully in accord with those reported
above (Procedure B).
Synthesis of the 2-sulfonylated Allenecarboxylates 7 According to
Procedure D
To a solution of n-BuLi (1.6 M in hexane, 3.13 mL, 5 mmol) in THF (20 mL) was
added, dropwise with stirring over 20 min, a solution of allenecarboxylate 3 (5.5 mmol)
in THF (10 mL) at −60◦C. The reaction mixture was stirred at this temperature for 1 h,
which was followed by the dropwise addition of a solution of methane-, trichloromethane-,

918
I. K. IVANOV AND V. CH. CHRISTOV
benzene-, or trimethylsilyloxy-sulfonyl chloride (5 mmol) in 10 mL of THF at −60◦C. After
the addition was completed, the mixture was warmed to r.t. and stirred for 2 h. Then the
mixture was quenched with 2N HCl, extracted with Et2O, washed with sat. NaCl, and dried
over anhydrous Na2SO4. After evaporation of the solvent, the residue was chromatographed
on column (silica gel, Kieselgel Merck 60 F254) using a mixture of hexane and EtOAc as
eluent to give the pure 2-sulfonylated allenoates 7a–j.
According to Procedure D, the ethyl 2-methanesulfonyl-4-phenyl-penta-2,3-dienoate
7c (yield: 0.81 g, 58%, 2.89 mmol) was prepared by lithiation of ethyl 4-phenylpenta-2,3-
dienoate 3c (1.11 g, 5.5 mmol) with BuLi and following reaction with methane-sulfonyl
1
chloride (0.57 g, 5 mmol). Light yellow oil. H NMR (CDCl3, 250 MHz): δ = 1.42 (t, J
= 7.1 Hz, 3H, MeCH2O), 2.07 (s, 3H, Me), 2.98 (s, 3H, MeSO2), 4.31 (q, J = 7.1 Hz,
3H, MeCH2O), 7.04–7.59 (m, 5H, Ph). 13C NMR (CDCl3, 62.9 MHz): δ = 14.0 (CH3),
18.2 (CH3), 41.2 (CH3), 62.0 (CH2), 97.4 (C), 109.1 (C), 128.0–139.2 (Ph), 162.5 (C),
214.8 (C). IR (film): 1126, 1340 (SO2), 1717 (C O), 1955 (C C C). Anal. Calcd. for
C9H14O4S (280.34): C, 59.98; H, 5.75; S, 11.44. Found: C, 60.04; H, 5.71; S, 11.49.
According to Procedure D, the ethyl 3-cyclohexylidene-trimethylsilyloxysulfonyl-
prop-2-enoate 7i (yield: 1.03 g, 62%, 3.1 mmol) was prepared by lithiation of the ethyl
3-cyclohexyliden-2-propenoate 3b (0.99 g, 5.5 mmol) with BuLi and following reaction
1
with trimethylsilyloxy-sulfonyl chloride (2.23 g, 5 mmol). Light yellow oil. H NMR
(CDCl3, 250 MHz): δ = 0.32 (s, 9H, Me3SiO), 1.31 (t, J = 7.0 Hz, 3H, Me), 1.42–2.36 (m,
10H, cyclohexyliden), 5.01 (q, J = 7.0 Hz, 2H, MeCH2O). 13C NMR (CDCl3, 62.9 MHz):
δ = 6.6 (CH3), 14.8 (CH3), 24.0 (CH2), 26.4 (CH2), 30.1 (CH2), 58.3 (CH2), 91.1 (C),
103.5 (C), 163.2 (C), 207.3 (C). IR (film): 1142, 1338 (SO2), 1956 (C C C). Anal.
Calcd. for C14H24O5SSi (332.49): C, 50.57; H, 7.28; S, 9.64. Found: C, 50.70; H, 7.19;
S, 9.72.
Synthesis of the 2-Sulfonylated Allenecarboxylates 7 According to
Procedure E
To a solution of n-BuLi (1.6 M in hexane, 3.13 mL, 5 mmol) in THF (20 mL) was
added, dropwise with stirring over 20 min, a solution of allenyl sulfone 5 (5.5 mmol) in
THF (10 mL) at −60◦C. The reaction mixture was stirred at this temperature for 1 h, which
was followed by the dropwise addition of a solution of chloroformate (0.55 g, 5 mmol) in
10 mL of THF at −60◦C. After the addition was completed, the mixture was warmed to
r.t. and stirred for 2 h. Then the mixture was quenched with 2N HCl, extracted with Et2O,
washed with sat. NaCl, and dried over anhydrous Na2SO4. After evaporation of the solvent,
the residue was chromatographed on column (silica gel, Kieselgel Merck 60 F254) using a
mixture of hexane and EtOAc as eluent to give the pure 2-sulfonylated allenoates 7a–g.
According to Procedure E, the ethyl 3-cyclohexylidene-2-trichloromethanesulfonyl-
prop-2-enoate 7e (yield: 1.19 g, 66%, 3.3 mmol) was prepared by lithiation of the 2-
cyclohexyliden-ethenyl trichloromethyl sulfone 5e (1.64 g, 5.5 mmol) with BuLi and fol-
1
lowing reaction with chloroformate. Light yellow oil. H NMR (CDCl3, 250 MHz): δ =
1.41 (t, J = 7.0 Hz, 3H, Me), 1.35–2.40 (m, 10H, cyclohexylidene), 4.29 (q, J = 7.0 Hz, 2H,
MeCH2O). 13C NMR (CDCl3, 62.9 MHz): δ = 15.2 (CH3), 23.9 (CH2), 26.0 (CH2), 33.3
(CH2), 62.4 (CH2), 91.2 (C), 106.3 (C), 110.4 (C), 155.7 (C), 212.6 (C). IR (film): 1132,
1337 (SO2), 1722 (C O), 1955 (C C C). Anal. Calcd. for C12H15O4SCl3 (361.67): C,
39.85; H, 4.18; S, 8.87. Found: C, 39.95; H, 4.28; S, 8.83.

SYNTHESIS OF 2-SULFONYLATED ALKA-2,3-DIENOATES
919
Supplemental materials available. Method of analysis, starting materials, and full
1
spectroscopic and characterization data including H and 13C NMR and IR spectral data
and elemental analyses for all new compounds and literature references to these data for
known compounds is listed.
REFERENCES
1. Patai, S. (Ed.), The Chemistry of Ketenes, Allenes and Related Compounds; John Wiley & Sons:
New York, 1980. (b) Landor, S. R. (Ed.): The Chemistry of the Allenes, Vol. 1–3; Academic Press:
London, 1982. (c) Pasto, D. J. Tetrahedron 1984, 40, 2805-2827. (d) Schuster, H. F.; Coppola, G.
M. Allenes in Organic Synthesis; John Wiley & Sons: New York, 1988. (e) Zimmer, R. Synthesis
1993, 2, 165-178. (f) Elsevier, C. J. In: R. W. Helmchen; J. Mulzer; and E. Schaumann (Eds.),
Methods of Organic Chemistry (Houben-Weyl); Vol. E21a; Thieme: Stuttgart; 1995; 537-566 .
(g) Krause, N.; Hashmi, A. S. K. (Eds.), Modern Allene Chemistry, Vol. 1 and 2; Wiley-VCH:
Weinheim, 2004. (h) Brummond, K. M.; DeForrest, J. E. Synthesis 2007, 795-818.
2. Clinet, J.-C.; Linstrumelle, G. Synthesis 1981, 11, 875-878. (b) Baudin, J.-B.; Julia, S. A.; Lorne,
R. Synlett 1991, 509-510. (c) Reich, H. J.; Mason, J. D.; Holladay, J. E. J. Chem. Soc., Chem.
Commun. 1993, 1481-1483. (d) Lambert, C.; Schleyer, P. R.; Wurthwein, E.-U. J. Org. Chem.
1993, 58, 6377-6389. (e) Zimmer, R. Synthesis 1993, 165-178. (f) Katritzky, A. R.; Verin, S.
V. J. Heterocycl. Chem. 1995, 32, 323-328. (g) Zhao, J.; Lui, Y.; Ma, S. Org. Lett. 2008, 10,
1521-1523.
3. Tsuboi, S.; Kuroda, H.; Takatsuka, S.; Fukawa, T.; Sakai, T.; Utaka, M. J. Org. Chem. 1993, 58,
5952-5957.
4. Braverman, S.; van Asten, P. F. T. M.; van der Linden, J. B.; Zwanenburg, B. Tetrahedron Lett.
1991, 31, 3867-3870.
5. Braverman, S.; Mechoulam, H. Israel J. Chem. 1967, 5, 71-75. (b) Smith, G.; Stirling, C. J. M.
J. Chem. Soc. C 1971, 1530-1535. (c) Braverman, S.; van Asten, P. F. T. M.; van der Linden, J.
B.; Zwanenburg, B. Tetrahedron Lett. 1991, 31, 3867-3870.
6. Conrads, M.; Mattay, J. Synthesis 1991, 11-14.
7. For our previous reports on bifunctionalized allenes see: (a) Christov, V. C.; Prodanov, B.
Phosphorus Sulfur Silicon Relat. Elem. 2000, 166, 265-273. (b) Christov, V. C.; Prodanov,
B.; Nikolova, R. Phosphorus Sulfur Silicon Relat. Elem. 2000, 166, 275-281. (c) Christov, V.
Ch.; Prodanov, B. Phosphorus Sulfur Silicon Relat. Elem. 2000, 166, 243-249. (d) Christov,
V. C.; Prodanov, B. Heterocycl. Commun. 2002, 8, 349-354. (e) Christov, V. C.; Prodanov, B.
Heterocycles 2002, 57, 1777-1780. (f) Christov, V. C.; Prodanov, B. Synth. Commun. 2004, 34,
1577-1588. (g) Christov, V. C.; Ivanova, J. G. Synth. Commun. 2006, 36, 2231-2244.
8. Christov, V. C.; Ivanov, I. K. Heterocycl. Commun. 2003, 9, 629-634. (b) Christov, V. C.; Ivanov,
I. K. Phosphorus Sulfur Silicon Relat. Elem. 2004, 179, 1681-1690.