Preparation and X-Ray Structure of 4-BrC6H4CNSC(Cl)N
Tristram Chivers*, Masood Parvez, Peter Zoricak
Department of Chemistry, The University of Calgary, Calgary, Alberta, Canada T2N 1N4
Z. Naturforsch. 52 b, 557-559 (1997); received September 5, 1996
Crystal Structure, 1,2,4-Thiadiazole, Intramolecular Cyclization
The title compound was obtained in 82% yield by the intramolecular cyclization of 4-
BrC6H4C(NSCCl3)[N(SiMe3)2] in CH2CI2 at 23°C. It crystallizes in the triclinic system, space
group PI, a = 7.957(3) Ä, b = 10.864(5) A, c = 5.625(1) A, a = 95.94(3)°, ß = 97.79(2)°, 7
= 100.72(3)°, V = 469.2(3) A3, and Z - 2. The bond lengths of the planar C2N2S ring indicate
partial 7r-delocalization.
Introduction
A variety of synthetic approaches to the 1,2,4-
thiadiazole ring system is available [1], For ex-
ample, the cyclocondensation of carbamidines
RC(NH2)(NH2)+Cl~ with CI3CSCI produces
RCNSC(C1)N [1]. In this note we report the syn-
thesis and X-ray structure of 3-p -bromophenyl-
5-chloro-l,2,4-thiadiazole (2 ), which was obtained
by the spontaneous intramolecular cyclization of
4 -BrC6H4C(NSCCl3)[N(SiMe3)2] (1 ), according to
eq. (1 ).
for 2.
thiadiazoles [5-10], the heterocyclic ring in 2 is es-
sentially planar and the bond lengths indicate some
7r-delocalization. Thus the S-N distance of 1.650(6)
A is significantly shorter than the predicted single
bond value of 1.73 A [11] and the sequence of C-
N bond lengths is 1.331(7), 1.380(8) and 1.302(7)
A (cf. single and double bond values of ca. 1.29
and 1.47 A, respectively [12]). The 4-BrC6H4 sub-
stituent is coplanar with the heterocyclic ring and
there are no significant intermolecular interactions.
The synthetic route represented by eq. (1) repre-
sents an alternative to the use ofcarbamidines [2] for
the synthesis of 1,2,4-thiadiazoles containing a 5-C1
substituent that can be subsequently functionalized.
Results and Discussion
The monothiolated benzamidine 1 was pre-
pared from 4 -BrC6H4CN2(SiMe3)3 [2,3] and
CCI3SCI (1:1 molar ratio) c f synthesis of
PhC(SCCl3)[N(SiMe3)2] [4], The lU NMR spec-
trum of 1 showed resonances for 4-BrC6H4 (an
AA’XX’ pattern centred at 6 8.80 and 7.56) and
SiMe3 groups (6 0.30) in the intensity ratio 4:18.
In addition, a second weak AA’XX’ pattern (6
8.15 and 7.65) attributed to 2 was evident. A so-
lution of 1 in CH9CI2 was kept for 72 h at 23 °C
and, after subsequent work-up, the heterocycle 2
was obtained in 82% yield. A small amount of 4-
BrC6H4C(NH)(NH2), the hydrolysis product of 1 ,
was also isolated.
Experimental Section
Preparation of 4-BrC6H4CNSC(Cl)N (2)
The structure of 2 was determined by X-ray
crystallography (see Fig. 1). The pertinent bond
lengths, bond angles and torsion angles are sum-
marized in Table I. In common with other 1,2,4-
A solution of CI3CSCI (0.60 g, 3.22 mmol) in 25 ml of
CH2CI2 was added dropwise to 4-BrC6H4CN2(SiMe3)3,
(1.37 g, 3.30 mmol) in 25 ml of CH2C12 at 23°C under
an atmosphere of N2. The reaction mixture was stirred
for 72h and then solvent and Me3SiCl were removed by
vacuum transfer to give a viscous yellow oil containing a
small amount of white powder. The oil was dissolved
* Reprint requests to Tristram Chivers.
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1997 Verlag der Zeitschrift für Naturforschung. All rights reserved.
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