Investigation of the halocyclization of S- and N-allyl derivatives of 2-benzothiazolethione

Article abstract of DOI:10.1007/s10593-011-0808-y

3-Allyl-2-benzothiazolethione reacts with iodine regiospecifically with annelation of the five-membered ring, while with bromine a mixture of the five- and six-membered rings are formed. 2-Allylthioben- zothiazole reacts with halogens with annelation of the five- and six-membered rings, while 2-(2-methyl-2-propenyl)thiobenzothiazole is annelated at the five-membered ring.

Full text of DOI:10.1007/s10593-011-0808-y

Chemistry of Heterocyclic Compounds, Vol. 47, No. 5, August 2011 (Russian original Vol. 47, No. 5, May, 2011)
INVESTIGATION OF THE HALOCYCLIZATION
OF S- AND N-ALLYL DERIVATIVES OF
2-BENZOTHIAZOLETHIONE
D. G. Kim1*, N. M. Sudolova1, and P. A. Slepuhin2
3-Allyl-2-benzothiazolethione reacts with iodine regiospecifically with annelation of the five-membered
ring, while with bromine a mixture of the five- and six-membered rings are formed. 2-Allylthioben-
zothiazole reacts with halogens with annelation of the five- and six-membered rings, while 2-(2-methyl-
2-propenyl)thiobenzothiazole is annelated at the five-membered ring.
Keywords: 2- and 3-halomethyl-2,3-dihydrothiazolo[2,3-b]benzothiazolium halides, 3-halo-3,4-dihyd-
ro-2H-[1,3]thiazino[2,3-b][1,3]benzothiazolium, halocyclization, X-ray crystallography.
Contradictory results on the bromocyclization of 2-allylthiobenzothiazole (1a) are described in the litera-
ture. For example, according to [1] 3-bromomethyl-2,3-dihydro[1,3]thiazolo[2,3-b][1,3]benzothiazolium bromide
(2a) is formed, whereas according to [2] – 3-bromo-3,4-dihydro-2H[1,3]thiazino[2,3-b][1,3]benzothiazolium bro-
mide (3a), and according to [3] – a mixture of compound 2a and 2-bromomethyl-2,3-dihydro[1,3]thiazolo[2,3-b]-
[1,3]benzothiazolium bromide (4a).
It should be noted that the 1H NMR spectrum of compound 2a obtained in [1] does not correspond to the
structure. Thus, a multiplet in the region of 6 ppm, characteristic for proton H-3 in the structures of the similar
compounds (3-halomethyl-2,3-dihydrothiazolo[3,2-a]pyridinium halides) is missing [4–6]. The structure of
1
compound 3a was confirmed by H NMR data and independent synthesis, but the yield was only 52% which
indicates the formation of other reaction products.
With the objective of investigating the direction of the halocyclization reaction, we have studied the
interaction of bromine and iodine with compounds 1a, 2-(2-methylprop-2-en-1-yl)thiobenzothiazole (1b), and
3-allylbenzothiazol-2(3H)-thione (5).
_______________
Celebrating the jubilee of Academician of the Russian Academy of Sciences V. N. Charushin.
* To whom correspondence should be addressed, e-mail: kim_dg48@mail.ru.
1 South Ural State University, 76 Lenin Prosp., Chelyabinsk 454080, Russia.
2 I. Ya. Postovskii Institute of Organic Synthesis, Ural Branch of the Russian Academy of Sciences, 22 Akade-
micheskaya/20 S. Kovalevskoi Str., Yekaterinburg 620990, Russia; e-mail: slepukhin@ios.uran.ru.
__________________________________________________________________________________________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, 760–765, May 2011. Original article
submitted March 31, 2011
0009-3122/11/4705-0631©2011 Springer Science+Business Media, Inc.
631

+
S
S
S
S
S
S
X2
N
N
N
+
X
X
R
R
A
B
1a,b
S
S
S
S
S
S
R
X
X
N
N
N
+
X
+
+
–
–
X
–
X2n+1
X
2a–d
3a,b
4a,b
S
S
S
S
N
N
+
X
5
1a, 2a,b R = H, 1b, 2c,d R = Me; 2a,c, 3a, 4a X = Br, 2b,d, 3b, 4b X = I; 4 a n = 0, b n = 1
Iodocyclization of compound 5 occurred regioselectivity to give a single reaction product,
2-iodomethyl-2,3-dihydro[1,3]-thiazolo[2,3-b][1,3]benzothiazolium triiodide (4b), the structure of which was
1
established by X-ray crystallography and H NMR spectroscopy. According to the X-ray results (Fig. 1) the
compound crystallizes in the centrosymmetric space group of the monoclinic class. The deviation of the atoms
of the benzothiazole ring from the mean squared plane is less than 0.02 Å. The dihydrothiazole ring of the cation
has the pseudoenvelope conformation, with atoms C(8), C(1), N(1), and S(2) lying practically in a single plain
(deviation less than 0.02Å), while atom C(9) lies 0.354 Å out of the plane. Atom S(2) is involved in the
π-conjugation system which appears as more then 0.14 Å length difference between the formally single bonds
C(1)–S(2) and S(2)–C(9) (Table 1) and the leveling of the C(1)–S(1), C(1)–S(2), and S(1)–C(7) bond lengths.
–
The I–I bond lengths in the I3 anion are practically the same, and the bond angle is close to 180°. The molecular
crystal packing is characterized by the presence of a shortened I(4)…I(1) contact (3.845(1) Å).
1
The H NMR spectrum of compound 4b has proton signals of the groups CH2I, =NCH2, and SCH at
3.83, 4.93, and 5.05 ppm respectively.
1
According to the H NMR spectrum, the reaction of compound 5 with bromine gave a mixture of two
compounds in a 13:1 ratio. The principal product is 2-bromomethyl-2,3-dihydro[1,3]thiazolo[2,3-b][1,3]benzo-
1
1
thiazolium bromide (4a), the H NMR spectrum of which is close to that of compound 4a. According to its H
NMR spectrum, the second compound is the bromide 3a.
Fig. 1 Overall view of the molecule of compound 4b from X-ray data.
632

TABLE 1. Chosen Bond Lengths (d) and Valence Angles (ω) of Compo-
und 4b from X-ray Data
Bond
d, Å
Angle
, deg
I(1)–I(2)
I(2)–I(3)
2.942(8)
2.944(8)
1.750(6)
1.688(6)
1.728(6)
1.869(6)
1.351(6)
1.408(7)
1.484(7)
2.136(6)
I(1)–I(2)–I(3)
C(1)–S(2)–C(9)
C(1)–S(1)–C(7)
S(1)–C(1)–S(2)
C(2)–N(1)–C(8)
C(1)–N(1)–C(2)
C(9)–C(10)–I(4)
N(1)–C(1)–S(1)
N(1)–C(1)–S(2)
C(1)–N(1)–C(8)
176.3(2)
91.7(3)
S(1)–C(7)
S(1)–C(1)
C(1)–S(2)
S(2)–C(9)
N(1)–C(1)
N(1)–C(2)
N(1)–C(8)
I(4)–C(10)
90.6(3)
131.6(4)
129.9(5)
114.3(5)
113.2(4)
113.2(4)
115.2(4)
115.7(5)
Comparison of the 1H NMR spectra of compounds 3a, 4a, and 4b allows us to establish the structures of
the products of halocyclization of compound 1a. The reaction of compound 1a with iodine in ethanol gave a 6:1
mixture of 3-iodomethyl-2,3-dihydro[1,3]thiazolo[2,3-b][1,3]benzothiazolium iodide (2b) and 3-iodo-3,4-dihyd-
ro-2H-[1,3]thiazino[2,3-b][1,3]benzothiazolium iodide (3b). The 1H NMR spectrum of compound 2b contains a
multiplet at 5.86 ppm, characteristic for proton H-3. It was suggested earlier that iodocyclization of compound
1a gave compounds 2b and 4b.
On bromination of compound 1a in CCl4 a precipitate is formed immediately which consists of a mix-
1
ture of the bromides 2a and 4a. The H NMR spectrum includes a multiplet at 5.75 ppm of the proton H-3 of
compound 2a. Then a 7.5:1 mixture of bromides 3a and 4a precipitates from the reaction mixture. The 1H NMR
spectrum of compound 3a coincides with the spectrum we had obtained earlier [3]. In our view compounds 2a
and 3a are formed by bromination of ion A and compound 4a from the thiiranium ion B.
TABLE 2. 1H NMR Spectra of Compounds 1a,b, 2a–d, 3a,b, 4a,b, and 5
Com-
pound
Chemical shifts, δ, ppm (J, Hz)
1a
1b
7.90–7.30 (4H, m, Н Ar); 6.02 (1H, m, =CH); 5.39 (1H, m, =CH2); 5.21 (1H, m, =CH2);
3.99 (2Н, m, SCH2)
7.90–7.21 (4Н, m, Н Ar); 5.12 (1Н, m, =СН2); 4.96 (1Н, m, =СН2); 4.02 (2Н, s, SCH2);
1.89 (3Н, s, СН3)
2a
2b
7.80–7.00 (4H, m, Н Ar); 5.75 (1Н, m, H-3); 4.50 (2H, m, CH2Br); 3.80 (2Н, m, SCH2)
8.35–7.70 (4Н, m, Н Ar); 5.86 (1Н, m, H-3); 4.54 (1Н, dd, J = 9.9, J = 12.2, CH2I);
3.97 (2Н, m, SCH2); 3.81(1Н, d. d, J = 2.4, J = 11.7, CH2I)
2c
2d
3a
3b
8.40–7.70 (4H, m, Н Ar); 4.65 (1H, m, CH2Br); 4.32 (1H, m, CH2Br); 4.17 (2Н, s,
SCH2); 2.12 (3Н, s, СН3)
8.35–7.65 (4H, m, Н Ar); 4.65 (1H, m, CH2Br); 4.37 (1Н, d, J = 11.7, SCH2); 4.32 (1H,
m, CH2Br); 4.13 (1Н, d, J = 11.8, SCH2); 2.15 (3Н, s, СН3)
8.40–7.80 (4H, m, Н Ar); 5.42 (1H, m, CHBr); 5.00 (2H, m, NCH2); 4.05 (2Н, m,
SCH2)
8.40–7.75 (4Н, m, Н Ar); 5.17 (1H, dd, J = 3.9, J =13.8, NCH2); 5.07 (1H, m, CHI);
4.89 (1H, dd, J = 8.5, J = 13.8, NCH2); 3.93–4.10 (2Н, m, SCH2)
4a
4b
5
8.35–7.65 (4H, m, Н Ar); 5.15 (1H, m, SCH); 5.05 (2H, m, NCH2); 4.10 (2H, m, CH2Br)
8.30–7.65 (4H, m, Н Ar); 5.05 (1H, m, SCH); 4.93 (1H, m, NCH2); 3.83 (2H, m, CH2I)
7.80–7.35 (4H, m, Н Ar); 5.90 (1H, m, =CH); 5.22 (1H, m, =CH2); 5.10 (2H, m,
NCH2); 5.08 (1H, m, =CH2)
633

Compound 1b, which has an electron-donor methyl group on the β-carbon atom of the allyl unit, reacts
with bromine and iodine with annelation of the five-membered ring to give 3-bromomethyl-3-methyl-2,3-di-
hydro[1,3]thiazolo[2,3-b][1,3]benzothiazolium bromide (2c) and 3-iodomethyl-3-methyl-2,3-dihydro[1,3]thi-
azolo[2,3-b][1,3]benzothiazolium iodide (2d) respectively. According to paper [7], if two methyl groups are on
the γ-carbon atom, halocyclization occurs with annelation of the six-membered ring.
EXPERIMENTAL
1H NMR spectra were recorded using Bruker DRX-400 (400 MHz) spectrometer in DMSO-d6 solutions
with TMS as internal standard.
2-Allylthiobenzothiazole (1a) was obtained by method [10] and 3-allylbenzothiazole-2-thione (5) by
method [11].
X-ray Crystallographic Analysis of Compound 4b, which was obtained by crystallization from ethanol,
was carried out with an Xcalibur 3 automatic four-circle diffractometer using standard procedures (MoKα
radiation, graphite monochromator, 295(2) K, ω/2θ scanning). A fragment of a brown prismatic crystal with the
dimensions 0.147 × 0.093 × 0.025 mm was used for the analysis. The crystal was monoclinic, space group P21/c,
parameters of the unit cell a = 14.955(2), b = 7.6846(11), c = 15.426(2) Å, β = 96.999(11)°, V = 1759.6(4) Å3, for
the empirical formula C10H9I4NS2, Z = 4, dcalc = 2.699 g/cm3, μ = 7.303 mm–1. In the range 2.74 < θ < 28.41°,
9313 reflections were collected, of which 4347 (Rint = 0.0402) were independent, and 2821 had I > 2σ(I),
complexity for θ = 28.41° (98.3%). Errors for adsorption were introduced analytically [8] using the multigrain
crystal model. The structure was solved and refined using the SHELX complex of programs [9]. All non-
hydrogen atoms were refined in the anisotropic approximation, hydrogen atoms were placed in geometrically
calculated positions and refined in the “rider” model with depend isotropic thermal parameters. The final
parameters of the refined structure were R1 = 0.0339, wR2 = 0.0544 (with reflections I > 2σ(I) R1 = 0.0943,
wR2 = 0.0564) (with all reflections at S = 0.993). The peaks of maxima and minima in the final electronic
density were Δρ = 1.249 and –0.901 e/Å3. The results of the X-ray analysis in the form of a cif-file have been
registered in the Cambridge Structural Database (deposit CCDC 819767). These data are freely accessible and
may be requested at the address www.ccdc.cam.ac.uk/data_request/cif or from the authors.
2-(2-Methylprop-2-en-1-yl)thiobenzothiazole (1b). 2-Benzothiazole (1.67 g, 10 mmol) and 3-chloro-
2-methylpropene (0.96 g, 10 mmol) were added to a solution of sodium (0.23 g, 10 mmol) in 2-propanol
(15 ml). The mixture was boiled for 3 h. After cooling it was filtered, the ethanol was evaporated, the residue
was treated with ether to give compound 1b as a yellow oil. Yield 1.75 g (79%). Found, %: C 59.35; H 4.91;
N 6.48; S 28.10. C11H11NS2. Calculated, %: C 59.69; H 5.01; N 6.33; S 28.97.
A Mixture of 3-Bromomethyl-2,3-dihydro[1,3]thiazolo[2,3-b][1,3]benzothiazolium (2a), 3-Bromo-
3,4-dihydro-2H-[1,3]thiazino[2,3-b][1,3]benzothiazolium (3a) and 2-Bromomethyl-2,3-dihydro[1,3]thiazo-
lo[2,3-b][1,3]benzothiazolium (4a) Bromides were prepared by method [3].
A Mixture of 2-Bromomethyl-2,3-dihydro[1,3]thiazolo[2,3-b][1,3]benzothiazolium (4a) and 3-Bro-
mo-3,4-dihydro-2H-[1,3]thiazino[2,3-b][1,3]benzothiazolium (3a) Bromides. A solution of Br2 (0.1 ml,
2 mmol) in CH2Cl2 (3 ml) was added dropwise to a solution of compound 5 (0.21 g, 1 mmol) in CH2Cl2 (2 ml)
with cooling in ice. After 24 h, the CH2Cl2 was evaporated, the residue was treated with acetone and filtered off.
Yield 0.24 g (66 %).
3-Bromomethyl-3-methyl-2,3-dihydro[1,3]thiazolo[2,3-b][1,3]benzothiazolium Bromide (2c). A
solution of Br2 (0.1 ml, 2 mmol) in CHCl3 (3 ml) was added dropwise to a solution of compound 1b (0.22 g,
1 mmol) in CHCl3 (2 ml) with cooling in ice. After 24 h, the CHCl3 was evaporated, the residue was treated with
acetone, and filtered off to give a yellow residue. Yield 0.23 g (60%); mp 152–155°C. Found, %: Br 42.52;
S 16.79. C11H11Br2NS2. Calculated, %: Br 41.93; S 16.83.
2-Iodomethyl-2,3-dihydro[1,3]thiazolo[2,3-b][1,3]benzothiazolium Triiodide (4b). Iodine (0.06 g,
0.1 mmol) in ethanol (3 ml) was added to a solution of compound 5 (0.022 g, 0.1 mmol) in ethanol (2 ml). The
634

brownish crystals (0.30 g, 65%), mp 150°C, were filtered off after 24 h. Found, %: I 71.25; S 8.84. C10H9I4NS2
Calculated, %: I 71.00; S 8.97.
Preparation of Compounds 2b,d, 3b (General Method). Iodine (0.5 g, 2 mmol) in ethanol (5 ml) was
added to a solution of compound 1a,b (1 mmol) in ethanol (3 ml). After 48 h, the solution was decanted, the
precipitate was dissolved in acetone (3 ml) and a solution of NaI·2H2O (0.37 g, 2 mmol) in acetone (3 ml) was
added. The yellow precipitate formed was filtered off.
A Mixture of 3-Iodomethyl-2,3-dihydro[1,2]thiazolo[2,3-b][1,3]benzothiazolium (2b) and 3-Iodo-
3,4-dihydro-2H-[1,3]thiazino[2,3-b][1,3]benzothiazolium (3b) Bromides. Yield 0.30 g (65%).
3-Iodomethyl-3-methyl-2,3-dihydro[1,3]thiazolo[2,3-b][1,3]benzothiazolium Iodide (2d). Yield
0.28 g (59%); mp 74–76°C. Found,%: I 53.68; S 13.44. C11H11I2NS2. Calculated, %: I 53.42; S 13.50.
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