Unexpected formation of 3-methylsulfanyl-2-phenyl-2-cyclobutenone in the reaction of 1,3-dilithio-2-propynylbenzene with methoxymethyl isothiocyanate

Full text of DOI:10.1023/B:RUJO.0000034923.10292.65

Russian Journal of Organic Chemistry, Vol. 40, No. 1, 2004, pp. 131-132. Translated from Zhurnal Organicheskoi Khimii, Vol. 40, No. 1, 2004,
pp. 140-141.
Original Russian Text Copyright Ó 2004 by Tarasova, Brandsma, Nedolya, Ushakov, Dmitrieva, Koroteeva.
SHORT
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Unexpected Formation
of 3-Methylsulfanyl-2-phenyl-2-cyclobutenone
in the Reaction of 1,3-Dilithio-2-propynylbenzene
with Methoxymethyl Isothiocyanate
O. A. Tarasova1, L. Brandsma2, N. A. Nedolya1, I. A. Ushakov1,
G. V. Dmitrieva1, and T. V. Koroteeva1
1 Favorskii Irkutsk Institute of Chemistry, Siberian Division, Russian Academy of Sciences,
ul. Favorskogo 1, Irkutsk, 664033 Russia
e-mail: olga@irioch.irk.ru
2Utrecht University, Utrecht, The Netherlands
Received October 29, 2003
2-phenyl-2-cyclobutenone (III) instead of N-methoxy-
methyl-3-methylsulfanyl-2-phenyl-2-cyclobuten-1-imine
(II) (Scheme 1). No corresponding thiophene was de-
tected among the products.
We recently found [1] that the reaction of 1,3-di-
lithiated 2-propynylbenzene with methyl isothio-cyanate,
followed by treatment of the primary adduct with a pro-
ton donor, base, and methyl iodide, results in formation of
three isomeric products: N-methyl-3-methylsulfan-yl-2-
phenyl-2-cyclobuten-1-imine, N,3-dimethyl-4-meth-ylene-
3-phenylthietan-2-imine, and 2-dimethylamino-3-
phenylthiophene at a ratio of 68:16:16 (overall yield 68–
77%). While continuing study of this unique reaction lead-
ing to four-membered cyclic systems, cyclobutenes and
thietanes (whose formation was not observed previously
in reactions of saturated carbanions with isothiocyanates
[2]), we replaced methyl isothiocyanate by methoxymethyl
isothiocyanate. The latter was successfully involved in
reactions with lithiated allenes and acetylenes, which were
reported in [3]. Unexpectedly, apart from iminothietane
I, from the reaction mixture we isolated 3-methylsulfanyl-
Obviously, cyclobutenone III is formed as a result
of hydrolytic cleavage of iminocyclobutene II. This pro-
cess is most likely to occur at the final stage of the stan-
dard treatment of the reaction mixture (with a saturated
aqueous solution of ammonium chloride at room tempera-
ture over a period of ~1 min). This is the first and still the
only example of extremely ready decomposition of imino
derivatives formed by reactions of unsaturated carban-
ions with isothiocyanates [1–3]. The observed reaction
not only deserves attention but may be regarded as a
new simple synthetic route to previously unknown
cyclobutenone derivatives which are difficult to obtain by
other methods.
Scheme 1.
1070-4280/04/4001-0131Ó2004 MAIK “Nauka/ Interperiodica”

TARASOVA et al.
132
Reaction of 1,3-dilithio-2-propynylbenzene with
999 s, 1029, 1067, 1103 s, 1126 s, 1196, 1238, 1288,
1377 s, 1445 s, 1584, 1600, 1635 s (C=C), 1714 s (C=N),
2723, 2824, 2868, 2927, 2972, 3024, 3059, 3087.
methoxymethyl isothiocyanate and methyl iodide.
A solution of 5.8 g (50 mmol) of 2-propynylbenzene in
110 ml of THF was cooled to –100°C, and 110 mmol of
butyllithium (68 ml of a 1.6 M solution in hexane) was added
over a period of ~1 min under a stream of argon. The
mixture was stirred for 10 min at 10–14°C and cooled to
-90°C, a solution of 5.15 g (50 mmol) of methoxymethyl
isothiocyanate in 5 ml THF was added in one portion, and
the mixture was stirred for 5 min at –70 to –65°C. The
cooling bath was removed, a mixture of 4 g (54 mmol) of
tert-butyl alcohol and ~2 ml of diethyl ether was added at
–55°C, and a solution of 6 g (54 mmol) of t-BuOK in 40 g
of DMSO was added at –40°C (the temperature sharply
rose to –20°C). The mixture was quickly (over a period
of 2–3 min) heated from –20 to 25°C and immediately
cooled to 10°C, and 22 g (150 mmol) of methyl iodide
was added. The mixture was stirred for 1.5 h at 25–40°C,
100 ml of a saturated aqueous solution of ammonium chlo-
ride was added, the mixture was stirred for ~1 min, the
organic phase was separated, and the aqueous phase was
extracted with diethyl ether (2´50 ml). The extracts were
combined with the organic phase, washed with three por-
tions of a saturated solution of ammonium chloride (to
remove DMSO), dried over MgSO4, and evaporated on
a rotary evaporator. The residue was distilled under re-
duced pressure (0.2–0.4 mm) to isolate 4.62 g of a frac-
tion boiling in the temperature range from 100 to 150°C
and ~4 g of a dark polymeric still residue which was not
analyzed. The liquid fraction was subjected to column
chromatography on aluminum oxide using hexane–diethyl
ether (3:1) as eluent. We isolated 2.72 g of a liquid mate-
3-Methylsulfanyl-2-phenyl-2-cyclobutenone
(III). Light yellow crystals, mp 105°C (from hexane–
methylene chloride, 5:1). 1H NMR spectrum, d, ppm:
2.52 s (3H, Me), 3.48 s (2H, CH2), 7.21 t (1H, p-H),
7.32 t (2H, m-H), 7.60 d (2H, o-H). 13C NMR spectrum,
dC, ppm: 16.76 (Me), 51.12 (C4), 126.58 (Co), 127.90 (Cp),
128.68 (Cm), 130.11 (Ci), 138.88 (C2), 166.89 (C3), 181.61
–1
(C=O). IR spectrum, n, cm : 466 w, 516, 575 w, 641 w,
695 s, 773 s, 840, 909 w, 962/976, 999 w, 1026 w, 1054,
1078, 1142, 1153 sh, 1180 w, 1264 s, 1285, 1312, 1335 w,
1421, 1444, 1482, 1574, 1603, 1726 s (C=O), 1809 w,
2119 w, 2856 w, 2926 w, 2954 w. Found, %: C 69.13;
H 5.33; S 17.25. C11H10OS. Calculated, %: C 69.44;
H 5.30; S 16.85.
Signals in the NMR spectra of compounds I and III
were assigned using NOESY, HMQC, and HMBC two-
dimensional techniques. Methoxymethyl isothiocyanate
was synthesized in ~65% yield by heating methyl
chloromethyl ether with KSCN in boiling pentane [4]. The
1H and 13C NMR spectra were recorded on a Bruker
DPX-400 spectrometer at 400.13 and 100.69 MHz, re-
spectively, using CDCl3 as solvent and HMDS as inter-
nal reference. The IR spectra were obtained on a Bruker
IFS-25 instrument from samples prepared as a thin film
(compound I) and a KBr pellet (III).
This study was performed under financial support
by the Russian Foundation for Basic Research (project
no. 02-03-33025).
1
rial containing (according to the H NMR data) 92% of
REFERENCES
thietane I (yield 21%), 1.02 g of cyclobutenone III as yel-
low crystalline substance (yield 11%), and 0.5 g of uniden-
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N-Methoxymethyl-3-methyl-4-methylene-3-
phenylthietan-2-imine (I). Yellow viscous liquid, nD20
=
1
1.5710. H NMR spectrum, d, ppm: 1.84 s (3H, Me),
3.36 s (3H, OMe), 4.76 s (2H, OCH2), 5.18 d (1H, HB,
2JAB = 4.4 Hz), 5.29 d (1H, HA), 7.29 t (1H, p-H), 7.34 t
13
(2H, m-H ), 7.59 d (2H, o-H). C NMR spectrum, dC,
ppm: 25.27 (Me), 57.17 (OMe), 75.62 (C3), 85.67
(OCH2), 104.71 (=CH2), 125.74 (Co), 127.52 (Cp), 128.82
(Cm), 140.29 (Ci), 146.91 (C4), 162.57 (C2). IR spectrum,
–1
n, cm : 500, 560, 629, 646, 699 s, 759, 782, 861, 924,
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 40 No. 1 2004