Chalcogen halides plus propargyl alcohols - Fascinating reaction pathways and products

Article abstract of DOI:10.1080/10426507.2010.507731

A convenient method to incorporate selenium into an organic molecule is reported. Selenium halides undergo smooth 1,2-addition to the triple bond of various propargylic alcohols under mild reaction conditions and with complete regio-and stereospecificity.

Full text of DOI:10.1080/10426507.2010.507731

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Phosphorus, Sulfur, and Silicon and the
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Chalcogen Halides Plus Propargyl
Alcohols—Fascinating Reaction Pathways
and Products
Samuel Braverman a , Dr Marina Cherkinsky a , Dr Tatiana Pechenick-
Azizi a , Mrs Yuliya Kalendar a & Professor Milon Sprecher a
a Department of Chemistry , Bar-Ilan University , Ramat-Gan, Israel
Published online: 12 Jul 2011.
To cite this article: Samuel Braverman , Dr Marina Cherkinsky , Dr Tatiana Pechenick-Azizi , Mrs Yuliya
Kalendar & Professor Milon Sprecher (2011) Chalcogen Halides Plus Propargyl Alcohols—Fascinating
Reaction Pathways and Products, Phosphorus, Sulfur, and Silicon and the Related Elements, 186:5,
1251-1254, DOI: 10.1080/10426507.2010.507731
To link to this article: http://dx.doi.org/10.1080/10426507.2010.507731
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Phosphorus, Sulfur, and Silicon, 186:1251–1254, 2011
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2010.507731
CHALCOGEN HALIDES PLUS PROPARGYL
ALCOHOLS—FASCINATING REACTION PATHWAYS
AND PRODUCTS
S. Braverman, M. Cherkinsky, T. Pechenick-Azizi,
Yu. Kalendar, and M. Sprecher
Department of Chemistry, Bar-Ilan University, Ramat-Gan, Israel
Abstract A convenient method to incorporate selenium into an organic molecule is reported.
Selenium halides undergo smooth 1,2-addition to the triple bond of various propargylic alcohols
under mild reaction conditions and with complete regio- and stereospecificity. The products
arising from these reactions depend on the nature of the selenium halide as well as on the
substitution pattern of the propargyl alcohol. Of special mechanistic interest is the syn-addition
and anti-Markovnikov orientation observed in all cases.
Keywords Divinyl selenides; electrophilic addition; regioselectivity; selenium dichloride;
selenium tetrachloride; stereoselectivity
INTRODUCTION
The field of sigmatropic rearrangements of allylic and propargylic esters of sulfur
acids at various oxidation states has proven to be a rich source of synthetically valuable
and mechanistically intriguing reactions. Some of the best examples are the reactions of
propargylic alcohols with sulfur dichloride1 and sulfur monochloride.2 The former results in
the formation of the appropriate sulfoxylates followed by tandem double [2,3]sigmatropic
rearrangement and cyclization of the generated diallenyl sulfone via a diradical intermediate
to the corresponding thiophene dioxide derivatives (Scheme 1).
Scheme 1
Received 30 June 2010; accepted 7 July 2010.
This work was supported by a grant from the Israel Science Foundation (Grant No. 919-05).
Address correspondence to S. Braverman, Department of Chemistry, Bar-Ilan University, Ramat-Gan 52900,
Israel. E-mail: bravers@mail.biu.ac.il
1251

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S. BRAVERMAN ET AL.
Due to the distinct characteristic features of organoselenium compounds in organic
synthesis3 as well as in biological systems,4 we decided to examine the reactivity of the
corresponding selenium halides with such substrates. We were surprised to discover that
the various aspects of the reaction of selenium halides with propargyl alcohols—that is,
chemiselectivity, regiospecificity, and stereospecificity—differ from expectations based on
known reactions of these alcohols with sulfur derivatives.
RESULTS AND DISCUSSION
We have found5 that in situ prepared selenium dihalides undergo smooth 1,2-addition
to the triple bond of various propargylic alcohols, resulting in the formation of symmetrical
Z,Z-bis(1-hydroxymethyl-2-halo)vinyl selenides (1) in high yields and in a completely
regio- and stereospecific manner (Scheme 2). Of special mechanistic interest is the syn-
addition and anti-Markovnikov orientation observed. The structures of these products have
been assigned on the basis of their NMR spectra, including COSY and NOESY experiments
as well as the Se-C coupling constants (measured from the 77Se satellites in the 13C NMR
spectra).
Scheme 2
Though no reaction of the hydroxyl group with selenium dihalides to yield selenoxy-
late esters (R-O-Se-O-R) could be detected, it appears that the hydroxyl group still plays
an important role, responsible for the above surprising regio- and stereochemical results.
The directing effect by the hydroxyl group was confirmed by the fact that the acetate and
tosylate esters of propargyl alcohols do not react even after prolonged periods of time, and
alkynes such as phenyl acetylene and propargyl bromide react very sluggishly and lead to
a mixture of possible isomers. The reaction of SeCl2 with homopropargyl alcohol provides
further evidence. In this case, substantial loss of stereo- and regioselectivity occurred. All
possible isomers were observed in the NMR spectra of the crude reaction mixture and a
Z-anti-Markovnikov product was chromatographically isolated as a major component.6
Further, we have found that SeCl4 adds readily to propargyl alcohols in a completely
regio- and stereospecific manner as selenium dihalides do. The reaction also proceeds via
syn-addition in an anti-Markovnikov manner. However, the final product depends on the
substitution in the starting propargyl alcohols.7 Thus, the reaction of α,α-dimethyl and α-
methylpropargyl alcohols with commercially available selenium tetrachloride gave, instead
of the expected divinylselenium dichlorides 2, products of unsymmetrical structure with
only one double bond. Based on 1H and 13C NMR spectra and HRMS elemental analysis we
identified these products as vinylselenium tetrachlorides 3 and explain their formation from
the intermediate divinylselenium dichloride 2 by spontaneous transposition of chlorines to
the double bond (Scheme 3).

CHALCOGEN HALIDES PLUS PROPARGYL ALCOHOLS
1253
Scheme 3
In the case of unsubstituted and γ -ethyl- and γ -phenyl-substituted propargylic alco-
hols, after careful low-temperature workup, we succeeded in isolating the divinylselenium
dichlorides 2c–e in high yields (Scheme 4). After standing in d6-acetone solution at room
temperature for 2–8 h, these unstable products undergo dechlorination to form the corre-
sponding selenides 1c–e with the same regio- and stereochemistry as the products obtained
from the reaction of the corresponding propargylic alcohols with SeCl2.5
Scheme 4
Upon standing in chloroform solution the dichlorovinylselenium dichloride 2c led
to the unsymmetrical selenide 3c (Scheme 5), in keeping with the above-mentioned trans-
position of chlorine from selenium atom in compounds 2 to the double bond to yield
products 3. In the case of γ -phenylpropargyl alcohol, the corresponding dichlorovinylse-
lenium dichloride 2e led to the isolation of (3-chlorobenzo[b]selenophen-2-yl)methanol 4
and (E)-2,3-dichloro-3-phenylprop-2-en-1-ol 5 (Scheme 5).
Scheme 5
Finally, the reaction of TeCl4 with propargyl alcohols was found to differ sharply from
that of SeCl4. The corresponding vinyl tellurium trichlorides 6 are obtained as a mixture
of regio- and stereoisomers (Scheme 6). The reaction shows a surprising sensitivity to
substitution on the propargylic moiety. Thus, 2-methylbut-3-yn-2-ol affords as the major
product (>90% according to 1H NMR spectrum of the crude reation mixture) the syn-adduct
with Markovnikov orientation (6a), whereas 1-phenyl-2-propyn-1-ol yielded as an isolated
product the anti-Markovnikov adduct 6b8 with E-configuration of the double bond.

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S. BRAVERMAN ET AL.
Scheme 6
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2. Braverman, S.; Pechenick, T.; Gottlieb, H. E.; Sprecher, M. J. Am. Chem. Soc. 2003, 125,
14290–14291.
3. Wirth, T., Ed. Organoselenium Chemistry: Modern Developments in Organic Synthesis. [In: Top.
Curr. Chem.]; Springer: Berlin, 2000; 259 pp.
4. Mugesh, G.; du Mont, W.-W.; Sies, H. Chem. Rev. 2001, 101, 2125–2179.
5. Braverman, S.; Jana, R.; Cherkinsky, M.; Gottlieb, H. E.; Sprecher, M. Synlett 2007, 2663–2666.
6. Braverman, S.; Cherkinsky, M.; Jana, R.; Kalendar, Y.; Sprecher, M. J. Phys. Org. Chem. 2010,
23, 1114–1120.
7. Braverman, S.; Pechenick-Azizi, T.; Gottlieb, H. E.; Sprecher, M. Synthesis 2011, 577–584.
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