(Dichloroiodo)benzene and lead(II) thiocyanate as an efficient reagent combination for stereoselective 1,2-dithiocyanation of alkynes

Article abstract of DOI:10.1016/S0040-4039(00)01909-2

An efficient steroselective 1,2-dithiocyanation of various alkynes has been accomplished by using a reagent combination of (dichloroiodo)benzene and lead(II) thiocyanate in dichloromethane at 0-5°C.

Full text of DOI:10.1016/S0040-4039(00)01909-2

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 42 (2001) 553–555
(Dichloroiodo)benzene and lead(II) thiocyanate as an efficient
reagent combination for stereoselective 1,2-dithiocyanation of
alkynes
Om Prakash,† Vijay Sharma, Hitesh Batra and Robert M. Moriarty*
Department of Chemistry, University of Illinois at Chicago, IL 60607, USA
Received 4 October 2000; accepted 25 October 2000
Abstract—An efficient stereoselective 1,2-dithiocyanation of various alkynes has been accomplished by using a reagent combina-
tion of (dichloroiodo)benzene and lead(II) thiocyanate in dichloromethane at 0–5°C. © 2001 Elsevier Science Ltd. All rights
reserved.
Recently, considerable attention has been directed
towards the use of the reagent combination of
organoiodine(III) compounds with metal salts1 and silyl
compounds2 in organic synthesis. In connection with our
ongoing studies on the synthetic utility of
organoiodine(III) reagents,3 we have reported that a
combination of (dichloroiodo)benzene and lead(II) thio-
cyanate (system i ) constitutes a very effective reagent for
a-thiocyanation of carbonyl-1a and b-dicarbonyl-4 com-
pounds. Such reactions are thought to proceed via in situ
generation of an I(III) species, namely, PhI(SCN)2 (1)
(Eq. (1)).1,4 To broaden the synthetic utility of system i
of Eq. (1) and to gain more insight into such combination
reagents, we investigated the reaction of various alkynes
with reagent system i.
1. The reaction of 1-phenyl-2-trimethylsilylethyne (2b)
with the reagent system i, which a priori, would be
expected to yield phenylethynyl(phenyl)iodonium
thiocyanate (4),5,6 in fact undergoes the addition
reaction (2b“3b).
2. The conversion 2i“3i indicates that the hydroxyl
group does not interfere in this thiocyanation
process.7
3. The conversion 2j“3j illustrates a case of 1,2-dithio-
cyanation of the CꢀC bond leaving the conjugated
CꢁC bond intact.
4. The effect of electron withdrawing groups is exem-
plified by the failure of the addition reaction of
dimethyl acetylenedicarboxylate (2k).
(1)
As expressed in Scheme 1 and Table 1, the reagent com-
bination of system i efficiently converted various
alkynes 2a–j into the corresponding 1,2-dithiocyanted
alkenes 3a–j in a stereoselective manner. The reaction
occurred at 0–5°C to give the E isomers 3 in moderate
to high yields with less than 5% of the corresponding
Z isomer.
Although the detailed mechanism of this thiocyanation
process is not determined, a plausible pathway involv-
ing PhI(SCN)2 (1) as reactive species and intermediates
of type 5 and 6 is outlined in Scheme 2. Since there is
no evidence for the existence of 1,1,4 it does not imply
Some noteworthy points on the results accomplished in
the present study (Table 1) are:
* Corresponding author. Fax: +312 9965242; e-mail: moriarty@
uic.com
†
On leave of absence from Kurukshetra University, Kurukshetra
136 119, India.
Scheme 1.
0040-4039/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(00)01909-2

554
O. Prakash et al. / Tetrahedron Letters 42 (2001) 553–555
Table 1. Thiocyanation of alkynes using PhICl2ꢂPb(SCN)2/CH2Cl2
the pathways and reactive species involved in this pro-
cess is in progress.
that 1 actually participates as a reactive species in this
reaction. The possibility of involvement of other reac-
tive species such as thiocyanogen1,2a,10,11 or thio-
cyanogen chloride8,9 in ionic or free radical mechanism
also exists. In a preliminary experiment, the thiocyana-
tion of phenylacetylene (2a) in the presence of 2,6-di-t-
butyl-4-cresol as a radical inhibitor in the dark under
the standard conditions of Scheme 1 gave 3a in the
same yield. More detailed work in order to determine
Finally, the use of the combination of PhICl2 and
Pb(SCN)2 in dichloromethane at 0–5°C provides a con-
venient and efficient way for the stereoselective 1,2-
dithiocyanation of various alkynes. Other reactive
functionalities such as double bonds and hydroxyl
groups present in the alkynes are not affected.

O. Prakash et al. / Tetrahedron Letters 42 (2001) 553–555
555
Scheme 2.
Acknowledgements
Ed.; Academic: New York, 1998; Vol. 69, Chapter 1, pp.
1–87. (d) Moriarty, R. M.; Prakash, O. Org. React. 1999,
54, 273–418. (e) Kitamura, T.; Fujiwara, Y. Org. Prepn.
Proced. Int. 1997, 29, 409–458. (f) Stang, P.; Zhdankin,
V. V. Chem. Rev. 1996, 96, 1123–1178. (g) Koser, G. F.
In The Chemistry of Halides, Pseudohalides and Azides,
Suppl. D2; Patai, S.; Rappoport, Z., Eds.; Wiley Inc:
New York, 1995; Chapter 21, p. 1173. (h) Kita, Y.;
Tohma, H.; Yakura, T. Trends in Organic Chemistry
1992, 3, 113. (i) Ochiai, M. Rev. Heteroatom Chem. 1989,
2, 92–111.
We thank the NIH under program P01 CA48112 for
financial support of this work.
References
1. (a) Prakash, O.; Rani, N.; Sharma, V.; Moriarty, R. M.
Synlett 1997, 1255–1256. (b) De Mico, A.; Margarita, R.;
Mariani, A.; Piancatelli, G. J. Chem. Soc., Chem Com-
mun. 1997, 1237–1238. (c) Ibid Tetrahedron Lett. 1996,
37, 1889–1890. (d) Kita, Y.; Okuno, T.; Egi, M.; Iio, K.;
Takeda, Y.; Akai, S. Synlett 1994, 1039–1040. (e) Kita,
Y.; Takeda, Y.; Okuno, T.; Egi, M.; Iio, K.; Kawagauchi,
K.; Akai, S. Chem. Pharm. Bull. 1997, 45, 1887–1890.
2. (a) Moira, B.; Margarita, R.; Parlanti, L.; Piancatelli, G.;
Malia, T. Tetrahedron Lett. 1998, 39, 3847–3848. (b)
Magnus, P.; Lacour, J.; Evans, P. A.; Roe, M. B.; Hulme,
C. J. Am. Chem. Soc. 1996, 118, 3406. (c) Kita, Y.;
Takeda, T.; Mihara, S.; Whelan, B. A.; Tohma, H. J.
Org. Chem. 1995, 60, 7144. (d) Zhdankin, V. V.; Tykwin-
ski, R.; Williamson, B. L.; Stang, P. J. Tetrahedron Lett.
1991, 32, 733–736.
4. Prakash, O.; Kaur, H.; Batra, H.; Rani, N.; Singh, S. P.;
Moriarty, R. M. J. Org. Chem., accepted for publication.
5. Various organoiodine(III) reagents react with terminal
alkynes
and
alkynylsilanes
to
give
similar
alkynyl(phenyl)iodonium salts, which subsequently
undergo reaction with nucleophiles.6
6. For
a
review of chemistry of alkynyl- and
alkenyl(phenyl)iodonium compounds see: Stang, P. J.
Angew. Chem., Int. Ed. Engl. 1992, 31, 274–285.
7. Alcohols are known to undergo oxidation with hyperva-
lent iodine reagents under suitable conditions.3a,3b
8. Bacon and Guy9 reported generation of thiocyanogen
chloride by the reaction of PhICl2 and Pb(SCN)2.
9. Bacon, R. G. R.; Guy, R. G. J. Chem. Soc. 1960,
318–324.
3. (a) Varvoglis, A. Hypervalent Iodine in Organic Synthesis;
Academic: New York, 1996. (b) Varvoglis, A. The
Organic Chemistry of Polycoordinated Iodine; VCH: New
York, 1992. (c) Moriarty, R. M.; Prakash, O. In
Advances in Heterocyclic Chemistry; Katritzky, A. R.,
10. Guy, R. G.; Cousins, D. M.; Hendreson, A. D.; Wilson,
C. L. Tetrahedron 1980, 36, 1839–1842.
11. Barluenga, J.; Martinez-Gallo, J. M.; Najera, C.; Yus, M.
J. Chem. Soc., Perkin Trans 1 1987, 1017–1019.
.