Scientific paper
Ring Expansion of ^-Aminobenzothiazolium Salts to Benzothiazines and Benzothiadiazines
Laszlo Filak,1 Betül Tekiner-Gulbas,2 Zsuzsanna Riedl,1 Gyongyvér Agnes Vaskó,1 Orsolya Egyed,1 Ismail Yal^in,2 Esin Aki-Sener2 and György Hajós1*
1 Chemical Research Center Hungarian Academy of Sciences, Pusztaszeri ut 59, H-1025 Budapest, Hungary
2Ankara University, Faculty oof Pharmacy, TR-06100 Tandogan, Ankara, Turkey
* Corresponding author: E^^ail: ghajos@che^res.hu
Received: 02-^0-2008 Dedicated to Professor Bi^^nko ^tano^nik on the occasion o^his JO^^" birthd^^
Abstract
.^-amino-2-benzylbenzothiazinium salts when reacted with aldehydes were found to undergo ring expansion reactions to give either benzothiadiazines or benzothiazines. This ambident reactivity was found to be influenced by the conjuga-tive nature of the aldehyde used.
Keywords: Ring expansion, thiadiazine, thiazine, ambident reactivity, reaction mechanism
1. Introduction
As mentioned in one of our recent publication,1 very limited information is known concerning the chemistry of ^-aminobenzothiazolium salts. Three decades ago, Tamu-ra and his co-workers described that treatment of ^-ami-no-2-methylbenzothiazolium mesylate (1) with aldehydes gives rise to a [1,3,4]benzothiazine derivative (2).1,2 Quite
recently we have published, furthermore, that benzyl substituted ^-aminobenzothiazolium salts (3) related to (1) are convenient starting materials for cyclization to tricyc-lic fused pyrazoles (4) (Scheme 1).1 As the benzyl substituted salts (3) in our hands contained an activated methy-lene group in the side chain, their conversion with aldehydes seemed of practical interest, which prompted us to extend our investigations into this direction.
.VCH3 RICHO

2. Results and Discussion
Reaction of butyraldehyde with benzyl substituted ^-aminobenzothiazolium salts (3) containing different substituents on the aryl group proceeded similar to that described by Tamura et al.2 3
tons (H2 at 4.76 and N=CH 8.87 ppm) characterize the benzothiazine structure in compound 6.
Benzothiazines of related structure have been already described by Takamizawa4 and, furthermore, similar ring transformation with benzothiazoles without any ^-amino moiety has been observed by Florio et al.5 6
			
			
			
			
			
			
			
			
			
			
a: X=H; b: X=Me; c: X=Br; d: X=CI; e: X=F
sScheme 2
Thus, transformation of 3a,b,d,e resulted in formation of benzothiadiazines 5a-d in moderate yields (2549%). Conversion of the p-bromophenyl derivative 3c with butyraldehyde, however, under the same reaction conditions yielded a mixture of two components: besides the expected benzothiadiazine (5e), a benzothiazine compound (6a) was also obtained (Scheme 2).
In order to explore a more extended synthetic possibility of this new type of ring expansion, the ^-amino salts 3a-e were transformed also by aryl aldehydes. Unexpectedly, in these reactions no benzothiadiazines (5) were formed but, instead, benzothiazines 6b-h were isolated from the reaction mixtures.
Analysis of the ^H-NMR spectra of 5 and 6 clearly indicate the structural differences between the two compounds. The compound with the benzothiadiazine structure (5) possesses an isolated methylene group (singlet at 4.0 ppm) and two protons (NH at 3.62 ppm, H3 at 4.4 ppm) coupled to each other. Contrarily, two singlet pro-
The observed ambident reactivity of 3 raised the question of a possible mechanism. The most plausible pathways of this dual behavior are illustrated in Fig 1.
Thus, most probably, the first step is reaction of the ^-amino function of 3 with the aldehyde to give an intermediate bearing an ^-azomethine side chain (a) which will be attacked by the hydroxide anion to give an addition product (b). In order to rationalize the later events involving ring transformations, one has to assume that this species undergoes deprotonation followed by an S-C cleavage to result in a ring opening to (c) which can adopt conformers (d) and (f). In conformer (d), an intramolecular attack ("A route") is favoured by the vicinity of the thiolate anion to the azomethine-carbon atom to yield (e) which can be shifted to the more stable tautomeric form (5). In the case of conformer (f), however, another cyclization ("B route") can occur: the sulphur atom can here attack the olefinic carbon atom adjacent to the aryl group to give (g) which, in the presence of air, can undergo spontaneous oxidation to 6.
Fig 1. Possible reaction mechanism of the ring expansion of A'-amino-2-benzylbenzothiazolium salts (3) to benzothiadiazines (5) and/or benzothia-zines (6).
This mechanism supposes that the relative electro-philicities of the azomethine-carbon atom and the olefinic carbon atom against the thiolate nucleophile may play the main role to decide whether 5 or 6 are formed. The fact that with all aryl aldehydes the B route was observed seems to be in good accordance with this supposition as the conjugation with participation of the N1 atom of the ring and the aryl group deactivates the azomethine-carbon atom (i.e. this atom becomes partially negative). One can, however, also assume by comparing of the outcomes of most of the reactions carried out with butyraldehyde with those carried out with arylaldehydes that a steric hindrance of the aryl group might direct the nucleophilic attack to the olefinic carbon atom, whereas in the case of smaller substituents the azomethine-carbon atom takes part in the reaction.
In order to exclude or to support this possibility, amino salt 3a was reacted with benzaldehyde and cyclo-hexyl aldehyde. These two aldehydes exert nearly similar
steric hindrance, but their conjugative properties are entirely different. The finding that exlusively 5f was formed with cyclohexyl aldehyde, whereas with benzaldehyde only 6i was obtained seems to support the importance of the conjugation rather than the possible steric hindrance.
Upon these results one can conclude that the pathway of the experienced ring expansion of ^-amino-2-benzylbenzothiazolium salts (3) strongly depends on the conjugation ability of the applied aldehyde. Thus, in the case of aliphatic or alicyclic aldehydes formation of thia-diazines is preferred, whereas in reactions with aryl aldehydes the reaction is directed towards formation of ben-zothiazines.
3. Experimental
Melting Points were determined on a Büchi apparatus and are uncorrected. The IR spectra were recorded on
a Thermo Nicolet Avatar 320 FT-IR spectrometer. NMR measurements were performed on Varian INOVA-200 or Varian INOVA-400 spectrometers equipped with a 5 mm inverse detection z-gradient probe. 1H and 13C NMR spectra were measured at room temperature (25 °C) in an appropriate solvent. 1H and 13C chemical shifts are expressed in ppm (5) referenced to residual solvent signals. The elemental analysis has been carried out with an Elementar Vario EL III apparatus (at the Analytical Laboratory for Organic Chemistry, Chemical Research Center, Hungarian Academy of Sciences, H-1025 Budapest, Pusztaszeri ut 59).
3. 1. General Procedure for Ring Expansion
of ^-aminobenzothiazolium Salts
To a mixture of a solution of the appropriate N-amino-benzothiazolium 4-methylbenzenesulfonate (3, 1 mmol) in acetonitrile (30 mL) and triethylamine (0.5 mL), the appropriate aldehyde (2 mmol) was added. The reaction mixture was heated under reflux and was monitored by TLC. After disappearance of the starting benzothiazolium salt (8-24 h), the obtained solution was evaporated onto silica. The product was then separated by flash chromato-graphy using silica as adsorbent and hexane-ethyl acetate 10:1 as the eluent.
1-(3-Propyl-2,3-dihydro-1H-benzo[e][1,3,4]thiadiazin-
1-yl)-2-p-tolylethanone	(5a). This compound was obtained by starting from 3-amino-2-(4-methylbenzyl)-1,3-ben-zothiazol-3-ium 4-methylbenzenesulfonate (3b, 1 mmol, 0.426 g) and butyraldehyde (0.2 mL) to give pale yellow crystals (0.160 g, 49%), mp 61-64 °C. Anal. Calcd for C19H22N20S (326.15): C, 69.90; H, 6.79; N, 8.58; S, 9.82. Found: C, 70.09; H, 7.12; N, 8.48; S, 10.16. IR (KBr) vmax: 3242, 2959, 1665, 1516, 1472, 1362, 1281, 1126, 1111, 753 cm-1. 1H NMR (CDCl3) 5 (ppm): 0.95 (3H, t, J = 7 Hz, C3"H3), 1.5 (2H, m, C2"H2), 1.65 and 1.84 (2H, m, C1"H2) 2.32 (3H, s, CH3'), 3.58 (1H, d, J = 7 Hz, NH), 3.96 (2H, m, COCH2), 4.40 (1H, m, H3), 7.05 (3H, m, H5, H6, H7), 7.14 (2H, m, H3', H5'), 7.24 (2H, m, H2', H6'), 7.76 (1H, m, H8). 13C NMR (CDCl3) 5 (ppm): 13.7, 18.7, 21.0, 37.0, 41.0, 63.4, 124.0, 124.1, 125.5, 126.1, 127.1, 129.0 (2C), 129.2 (2C), 131.9, 133.3, 136.3, 172.0.
2-Phenyl-1-(3-propyl-2,3-dihydro-1H-benzo[e][1,3,4]
thiadiazin-1-yl)ethanone (5b). This compound was obtained by starting from 3-amino-2-benzyl-1,3-benzothia-zol-3-ium 4-methylbenzenesulfonate (3a, 1 mmol, 0.411 g) and butyraldehyde (0.2 mL) to give pale yellow cry-stals(0.149 g, (48%), mp 114-116 °C. Anal. Calcd for C18H20N20S (312.13): C, 69.20; H, 6.45; N, 8.97; S, 10.26. Found: C, 69.44; H, 6.80; N, 8.91; S, 10.63. (KBr) vlax: 3241, 2959, 1665, 1471, 1364, 1281, 1129, 914, 746 cH-"1. 1H NMR (CDCl3) 5 (ppm): 0.95 (3H, t, J = 6.5 Hz, C3"H3), 1.5 (2H, m, C2"H2), 1.62 and 1.82 (2H, m,
C1"H2), 3.62 (1H, d, J = 7 Hz, H2), 4.0 (2H, m, C(0) CH2), 4.4 (1H, m, H3), 7.0-7.12 (3H, m, H5, H6, H7), 7.2(2-7.40 (5H, m, H2', H3', H4', H5', H6'), 7.76 (1H, d, J = 8 Hz, H8). 13C NMR (CDCl3) 5 (ppm): 14.0 (C3"), 19.0 (C2"), 37.2 (C1"), 41.7 (C(0) CH2), 63.6 (C3), 124.3 and 124.4 and 125.8 (C5, C6, C8), 126.3 (C4a), 127.0 (C7), 127.3 and 127.4 and 128.8 and 129.4 (C1', C2', C3', C4', C5', C6'), 135.2 (C8a), 172.3 (C=0).
2-(4-Chlorophenyl)-1-(3-propyl-2,3-dihydro-1H-ben-zo[e][1,3,4]thiadiazin-1-yl)ethanone (5c). This compound was obtained by starting from 3-amino-2-(4-chloro-benzyl)-1,3-benzothiazol-3-ium 4-methylbenzenesulfo-nate (3d, 1 mmol, 0.445 g) and butyraldehyde (0.2 mL) to give pale yellow crystals (0.170 g 49%), mp 114-116 °C. Anal. Calcd for C18H19ClN2OS (346.09) C, 62.33; H, 5.52; N, 8.08; S, 9.24. Found: C, 62.29; H, 5.47; N, 8.03; S, 9.22. IR (KBr) vlax: 3273, 2959, 1674, 1475, 1356,
1283,	1128, 1088, 8104, 753 cm-1. 1H NMR (CDCl3) 5 (ppm): 0.97 (3H, t, J = 7 Hz, C3"H3), 1.55 (2H, m, C2"H(), 1.62 and 1.82 (2H, m, C1"H(), 3.61 (1H, d, J = 7 Hz, ^(H), 3.97 (2H, m, C(0) CH(, 4.44 (1H, m, H3), 7.0-7.10 (3H, m, H5, H6, H7), 7.^0-7.40 (4H, m, H2', H3', H5', H6'), 7.71 (1H, m, H8). 13C NMR (CDCl3) 5 (ppm): 13.7, 18.8, 37.0, 40.6, 63.3, 124.1, 124.2, 125.7, 125.9, 127.2, 127.3, 128.6 (2C), 130.5 (2C), 132.8, 133.5, 170.7.
2-(4-Fluorophenyl)-1-(3-propyl-2,3-dihydro-1H-ben-zo[e][1,3,4]thiadiazin-1-yl)ethanone (5d). This compound was obtained by starting from 3-amino-2-(4-fluro-robenzyl)-1,3-benzothiazol-3-ium 4-methylbenzenesulfo-nate (3e, 1 mmol, 0.430 g) and butyraldehyde (0.2 mL) to give pale yellow crystals (0.170 g 49%), mp 130-131 °C. HRMS (EI): M+, found: 330.1203. C18H19FN(OS required: 330.1202. IR (KBr) vlax: 3274, 2960, 1669, 1511, 1475, 1434, 1358, 1279, 1127, 819, 754 cm-1. 1H NMR (CDCl3) 5 (ppm): 0.96 (3H. t, J = 7 Hz, C3"H3), 1.53 (2H, m, C2"H(), 1.62 and 1.90 (2H, m, C1"H() 3.62 (1H, d, J = 7 Hz, NIH), 3.96 (2H, m, C(0) CH(), 4.46 (1H, m, H3), 7.06 (5H, m, H5, H6, H7, H3', H5'), 7.30 (2H, m, H2', H6'), 7.74 (1H, m, H8). 13C NMR (CDCl3) 5 (ppm): 13.7, 18.8, 37.1, 40.4, 63.4, 115.3 (2C, d, (JCF ^ 23.5 Hz), 124.0, 124.1 (C8, C6), 125.7, 126.1, 127.2, :130.6 (2C, d, 3Jc,f = 9 Hz), 133.1, 162.0 (d, 1JC,F = 235 Hz), 171.8.
2-(4-Bromophenyl)-1-(3-propyl-2,3-dihydro-1H-ben-zo[e][1,3,4]thiadiazin-1-yl)ethanone (5e). This compound was obtained by starting from 3-amino-2-(4-bromo-benzyl)-1,3-benzothiazol-3-ium 4-methylbenzenesulfo-nate (3c, 1 mmol, 0.49 g) and butyraldehyde (0.2 mL) to give pale yellow crystals (0.040 g 10%), mp 96-98 °C. Anal. Calcd for C18H19BrN(OS (391.33): C, 55.25; H, 4.89; N, 7.16; S, 8.19. I^ound: C, 55.15; H, 4.85; N, 7.15; S, 8.31.IR (KBr) vlax: 3275, 2958, 1675, 1475, 1359,
1284,	1128, 1071, 1((X2, 752 cm-1. 1H NMR (CDCl3) 5
(ppm): 0.95 (3H, t, J = 6.5 Hz, C3"H3), 1.4-1.8 (4H, m, C2"H2, C1"H2), 3.61 (1H, d, J = 7 Hz, H2-NH), 3.95 (2H, m, C(O) CH2), 4.44 (1H, m, H3), 7.0-7.12 (3H, m, H5, H6, H7), 7.2^ (2H, m, H3', H5'), 7.46 (2H, m, H2', H6'), 7.74 (1H, m, H8). 13C NMR (CDa3) d (ppm): 12.5, 18.0, 35.9, 39.8, 62.2, 119.8, 123.1, 123.2, 124.7, 126.2, 128.2, 129.9 (2C), 130.7 (2C), 133.1, 170.5.
1-(3-Cyclohexyl-2,3-dihydro-1H-benzo[e][1,3,4]thia-diazin-1-yl)-2-phenylethanone (5f). This compound was obtained by starting from 3-amino-2-benzyl-1,3-benzot-hiazol-3-ium 4-methylbenzenesulfonate (3a, 1 mmol, 0.411 g) and cyclohexanecarbaldehyde (0.25 mL) to give pale yellow crystals (0.08 g, 23%), mp 136-137 °C. Anal. Calcd for C21H24N2OS (352.16): C, 71.55; H, 6.86; N, 7.95. Found: C, 71.40; H, 7.06; N, 7.83. IR (KBr) vmax: 3275, 2931, 2841, 1688, 1474, 1440, 1352, 1279, 1119, 757 cm-1. 1H NMR (CDCl3) 5 (ppm): 1.23 and 1.73 and 2.06 (11H, m, H-cyclohexyl), 3.60 (1H, d, J = 7 Hz, NH), 3.98 (2H, m, COCH2), 4.45 (1H, dd, J = 7 + 12 Hz, H3), 7.06 (3H, m, H5, H6, H7), 7.28 (5H, m, H2', H3', H4', H5', H6'), 7.74 (1H, m, H8). 13C NMR (CDCl3) 5 (ppm): 25.7, 25.2, 28.5, 29.4, 41.0, 42.2, 69.1, 12^.9, 124.0, 125.5, 126.7, 127.4, 128.5 (2C), 129.2 (2C), 133.3, 135.2, 172.3.
(2H, m, H2', H6'), 8.88 (1H, s, N=CH). 13C NMR (CDC-l3) 5 (ppm): 21.8, 47.6, 119.1, 120.6, 122.5, 124.6, 127.6, 128.2, 128.7 (2C), 129.7 (2C), 129.9 (2C), 130.7, 132.0 (2C), 133.8, 139.5, 142.7, 162.1, 166.2.
(£)-2-(4-Chlorophenyl)-4-(4-methylbenzylideneami-no)-2H-benzo[Ä][1,4]thiazin-3(4Ä)-one (6c). This compound was obtained by starting from 3-amino-2-(4-chloro-benzyl)-1,3-benzothiazol-3-ium 4-methylbenzenesulfo-nate (3d, 1 mmol, 0.445 g) and 4-methylbenzaldehyde (0.2 mL) to give pale yellow crystals (0.130 g, 33%), mp 158-161 °C. Anal. Calcd for C22H17ClN2OS (392.08): C, 67.25; H, 4.36; N, 7.13; S, 8.16. Found: C, 66.85; H, 4.27; N, 7.04; S, 8.27. IR (KBr) vmax: 2911, 1648, 1605, 1489, 1337, 1090, 749 cm-1. 1H Nl^R (CDCl3) 5 (ppm): 2.41 (3H, s, CH3'), 4.76 (1H, s, H2), 7.03 (1H, dd, J = 8.2 + 7.5 Hz, H7), 7.21 (1H, dd, J = 8.0 + 7.5 Hz, H6), 7.26 (4H, m, H3', H5', H3", H5"), 7.31 (2H, m, H2", H6"), 7.35 (1H, d, J = 8.2 Hz, H8), 7.42 (1H, d, J = 8.0 Hz, H5), 7.76 (2H, m, H2', H6'), 8.87 (1H, s, N=CH). 13C NMR (CDCl3) 5 (ppm): 21.7 (CH3), 47.3 (C2), 118.9 (C5), 120.5 (C8a),
124.4	(C7), 127.4 (C6), 128.0 (C8), 128.5 (C2', C6'), 128.8 (C3", C5"), 129.4 (C2", C6"), 129.6 (C3', C5'),
130.5	(C1'), 133.0 (C1"), 134.2 (C4"), 139.3 (C4a), 142.5 (C4'), 162.0 (C3), 166.1 (N=CH).
(£)-2-(4-Bromophenyl)-4-(butylideneamino)-2H-ben-zo[^][1,4]thiazin-3(4H)-one (6a). This compound was obtained by starting from 3-amino-2-(4-bromobenzyl)-1,3-benzothiazol-3-ium 4-methylbenzenesulfonate (3c, 1 mmol, 0.49 g) and butyraldehyde (0.2 mL) to give pale yellow crystals 0.140 g (36%), mp 103-105 °C,. Anal. Calcd for C18H17BrN2OS (388.02): C, 55.53; H, 4.40; N, 7.20; S, 8.24. Found: C, 55.20; H, 4.23; N, 7.11; S, 8.27. IR (KBr) vmax: 2954, 2924, 1656, 1585, 1485, 1475, 1333, 1268, 1012m,"751 cm-1. 1H NMR (CDCl3) 5 (ppm): 1.05 (3H, t, J = 8, C3'H3), 1.71 (2H, m, C2'I12), 2.55 (2H, m, C1'H2), 4.70 (1H, s, H2), 7.03 (1H, t, J = 8 Hz, H7), 7.23 (2H, m, H3", H5"), 7.30 (3H, m, H5, H6, H8), 7.41 (2H, m, H2", H6"), 8.15 (1H, t, J = 5 Hz, N=CH). 13C NMR (CDCl3) 5 (ppm): 13.7, 19.2, 35.2, 46.9, 118.1, 119.9, 122.3, 124.1, 127.3, 128.1, 129.6 (2C), 131.8 (2C), 133.7, 138.8, 161.8, 169.2.
(£)-4-(4-Methylbenzylideneamino)-2-phenyl-2H-ben-zo[Ä][1,4]thiazin-3(4Ä)-one (6d). This compound was obtained by starting from 3-amino-2-benzyl-1,3-benzo-thiazol-3-ium 4-methylbenzenesulfonate (3a, 1 mmol, 0.411 g) and 4-methylbenzaldehyde (0.2 mL) to give 6d, pale yellow crystals (0.105 g, 29%), mp 135-138 °C. Anal. Calcd for C22H18N2OS (358.11): C, 73.71; H, 5.06; N, 7.82; S, 8.95. Found: C, 73.35; H, 5.05; N, 7.78; S, 9.21. IR (KBr) vmax: 3086, 3056, 2920, 1668, 1607, 1475, 1450, 1310, 1225, 765 cm-1. 1H NMR (CDCl3) 5 (ppm): 2.41 (3H, s, CH3'), 4.82 (1H, s, H2), 7.05 (1H, t, J = 6 Hz, H7), 7.26 (10H, m, H3', H5', H3", H5", H2", H4", H6", H5, H6, H8), 7.77 (2H, m, H2', H6'), 8.92 (1H, s, N=CH). 13C NMR (CDCl3) 5 (ppm): 22.0, 48.0, 118.9, 121.0, 124.4, 127.3, 127.9 (2C), 128.1, 128.3, 128.4 (2C), 128.7 (2C), 129.5 (2C), 130.8, 134.6, 139.5, 142.4, 162.5, 165.8.
(£)-2-(4-Bromophenyl)-4-(4-methylbenzylideneami-no)-2H-benzo[^][1,4]thiazin-3(4H)-one (6b). This compound was obtained by starting from 3-amino-2-(4-bromo-benzyl)-1,3-benzothiazol-3-ium 4-methylbenzenesulfonate (3c, 1 mmol, 0.49 g) and 4-methylbenzaldehyde (0.2 mL) to give pale yellow crystals (0.131 g, 30%), mp 178-180 °C. HRMS (El): M+, found: 436.0252. C22H17Br-N2OS requires: 436.0245. IR (KBr) vmax: 291^, 1^48, 1^05, 1484, 1338, 1011, 749 cm-1. 1H NfMR (CDCl3) 5 (ppm): 2.40 (3H, s, CH3'), 4.76 (1H, s, H2), 7.05 (1H, t, J = 8 Hz, H7), 7.26 (6H, m, H3", H5", H3', H5', H8, H5), 7.34 (1H, t, J = 8 Hz, H6), 7.43 (2H, m, H2", H6"), 7.76
(£)-2-(4-Fluorophenyl)-4-(4-methylbenzylideneami-no)-2H-benzo[^][1,4]thiazin-3(4H)-one (6e). Starting from 3-amino-2-(4-flurorobenzyl)-1,3-benzothiazol-3-ium 4-methylbenzenesulfonate (3e, 1 mmol, 0.430 g) and 4-methylbenzaldehyde (0.2 mL) to give pale yellow crystals (0.075 g, 20%), mp 112-115 °C. HRMS (El): M+, found: 376.1055. C22H17FN2OS requires: 376.1046. IR (KBr) vmax: 2927, 1.;.53, 1603, 1506, 1476, 1330, 1229, 1161, 74^ cm-1. 1H NMR (CDCl3) 5 (ppm): 2.42 (3H, s, CH3'), 4.79 (1H, s, H2), 6.98 (2H, m, H2", H6") 7.06 (1H, t, J = 5 Hz, H7), 7.23 (1H, t, J = 5 Hz, H6), 7.27 (2H, m,
H3', H5'), 7.35 (2H, m, H3", H5"), 7.38 (1H, d, J = 5 Hz, H8), 7.43 (1H, d, J = 5 Hz, H5), 7.76 (2H, m, H2', H6'), 8.90 (1H, s, N=CH). 13C NMR (CDCl3) 5 (ppm): 21.8, 47.3, 115.6 (2C, d, 2JCF = 26.5 Hz), 118.9, 120.7, 124.4,
127.3,	128.0, 128.5 (2C), 129.6 (2C), 129.8 (2C, d, 3JCF = 9 Hz), 130.2, 130.5, 139.3, 142.5, 143.8, 162.5 (d, = 245 Hz), 166.0.	,
(£)-4-(4-Methylbenzylideneamino)-2-p-tolyl-2H-ben-zo[Ä][1,4]thiazin-3(4Ä)-one (6f). This compound was obtained by starting from 3-amino-2-(4-methylbenzyl)-1,3-benzothiazol-3-ium 4-methylbenzenesulfonate (3a, 1 mmol, 0.426 g) and 4-methylbenzaldehyde (0.2 mL) to give pale yellow crystals (0.238 g, 64%), mp 155-157 °C. Anal. Calcd for C23H20N2OS (320.08): C, 74.16; H, 5.41; N, 7.52; S, 8.61. I^oiind: C, 74.00; H, 5.43; N, 7.48; S, 8.65. IR (KBr) vmax: 2915, 1651, 1605, 1510, 1476, 1446, 1333, 750, 503 cm-1. 1H NMR (CDCl3) 5 (ppm): 2.25 (3H, s, CH3"), 2.40 (3H, s, CH3'), 4.80 (1H, s, H2), 7.04 (1H, t, J = ^ Hz, H7), 7.11 (2H, m, H3", H5"), 7.24 (1H, t, J = 8 Hz, H6), 7.26 (2H, m, H2", H6"), 7.27 (2H, m, H3', H5'), 7.35 (1H, d, J = 8 Hz, H8), 7.43 (1H, d, J = 8 Hz, H5), 7.75 (2H, m, H2', H6'), 8.92 (1H, s, N=CH). 13C NMR (CDCl3) 5 (ppm): 21.3, 21.9, 47.9, 119.1, 121.4, 124.5, 127.4, 128.1, 128.2 (2C), 128.7 (2C), 129.6 (2C), 129.8 (2C), 130.9, 131.7, 138.2, 139.7, 142.6, 162.8, 166.0.
(£)-4-(4-Methoxybenzylideneamino)-2-phenyl-2H-benzo[^][1,4]thiazin-3(4H)-one (6g). This compound was obtained by starting from 3-amino-2-benzyl-1,3-ben-zothiazol-3-ium 4-methylbenzenesulfonate (3a, 1 mmol, 0.411 g) and 4-methoxybenzaldehyde (2 mmol, 0.272 g) to give pale yellow crystals (0.120 g, 32%), mp 135-137 °C. Anal. Calcd for C11H18N1O1S (374.11): C, 70.57; H, 4.85; N, 7.48; S, 8.56. Found: C, 70.32; H, 5.06; N, 7.46; S, 8.51. IR (KBr) vmax: 2916, 1658, 1599, 1514, 1316, 1260, 1168, 1030, 82^8, 752 cm-1. 1H NMR (CDCl3) 5 (ppm): 3.85 (3H, s, OCH3), 4.81 (1H, s, H2), 6.96 (2H, m, H3', H5'), 7.03 (1H, t, J= 8 Hz, H7), 7.31 (8H, m, H2", H3", H4", H5", H6", H5, H6, H8), 7.82 (2H, m, H2', H6'), 8.83 (1H, s, N=CH). 13C NMR (CDCl3) 5 (ppm): 47.8, 55.4, 114.3 (2C), 118.7, 120.8, 124.1, 1^5.9, 127.1, 128.0 (2C), 128.1, 128.6 (2C), 130.1, 130.2 (2C), 134.6,
139.4,	162.3, 162.6, 165.8.
(£)-2-(4-Chlorophenyl)-4-(4-methoxybenzylideneami-no)-2H-benzo[^][1,4]thiazin-3(4H)-one (6h). This compound was obtained by starting from 3-amino-2-(4-chloro-benzyl)-1,3-benzothiazol-3-ium 4-methylbenzenesulfo-nate (3d, 1 mmol, 0.445 g) and 4-methoxybenzaldehyde (2 mmol, 0.272 g) to give pale yellow crystals (0.082 g,
20%), mp 145-147 °C. Anal. Calcd for C11H17ClN1O1S (408.07): C, 64.62; H, 4.19; N, 6.85; S, 7.84. F^ound: C, 64.37; H, 4.26; N, 6.88; S, 8.24. IR (KBr) vmax: 2930, 1650, 1598, 1514, 1489, 1315, 1258, 1170, 1028, 837, 756 cm-1. 1H NMR (CDCl3) 5 (ppm): 3.84 (3H, s, OCH3), 4.80 (1H, s, H2), 6.98 (2H, m, H3', H5'), 7.05 (1H, t, J = 8 Hz, H7), 7.21 (1H, d, J = 8 Hz, H8), 7.30 (5H, m, H6, H2", H3", H5", H6"), 7.41 (1H, d, J = 8 Hz, H5), 7.82 (2H, m, H2', H6'), 8.80 (1H, s, N=CH). 13C NMR (CDC-l3) 5 (ppm): 47.1, 55.4, 114.3 (2C), 118.8, 120.4, 124.3, 125.7, 127.3, 128.0, 128.8 (2C), 129.4 (2C), 130.3 (2C), 133.1, 134.1, 139.2, 161.9, 162.8, 166.2.
(£)-4-(Benzylideneamino)-2-phenyl-2H-benzo[^][1,4] thiazin-3(4Ä)-one (6i). This compound was obtained by starting from 3-amino-2-benzyl-1,3-benzothiazol-3-ium 4-methylbenzenesulfonate (3a, 1 mmol, 0.411 g) and benzaldehyde (2 mL) to give pale yellow crystals (0.089 g, 26%), mp 109-110 °C. Anal. Calcd for C11H1gN1OS (344.10): C, 73.23; H, 4.68; N, 8.13. Found: C, 7^.95; H, 4.44; N, 8.12. IR (KBr) vmax: 3029, 1671, 1470, 1450, 1444, 1308, 1226, 1214, 75(:) cm-1. 1H NMR (CDCl3) 5 (ppm): 4.82 (1H, s, H2), 7.05 (1H, t, J = 8 Hz, H7), ^.22 (1H, t, J = 8, H6), 7.4-7.5 (10H, m, H5, H8, H2", H3", H4", H5", H6', H3', H4', H5'), 7.86 (2H, m, H2', H6'), 9.02 (1H, s, N=CH). 13C NMR (CDCl3) 5 (ppm): 47.6, 118.5, 120.6, 123.9, 126.7, 127.5 (2C), 127.6, 127.7, 127.9 (2C), 128.1 (2C), 128.3(2C), 131.2, 133.0, 134.0, 139.0, 162.1, 164.6.
4. Acknowledgment
Financial support of projects GVOP-3.2.1-2004-04-0311/3.0, GVOP-3.2.1-2004-0210/3.0, and COST BM0701 (ATENS) are gratefully acknowledged.
5. References
1.	B. Tekiner-Gulbas, L. Filak, Gy.Vaskó, O.Egyed, I.Yalfin, E. Aki-Sener, Zs.Riedl, Gy. Hajós, Heterocycles, 2008, 75, 1005-1011.
2.	Y. Tamura, H. Hayashi, M. Ikeda, Synthesis, 1974, 116-117.
3.	Y. Tamura, H. Hayashi, J-H. Kim, J. Minamikawa, E. Saeki, H. Ikeda, Heterocycles, 1974, 2, l(9-l(9.
4.	A. Takamizawa, H. Sato, Y. Sato, Chem. Pharm. Bull. 1972, 20, 892-900.
5.	S. Florio, L. Troisi, V. Capriati, Tetrahedron Lett. 1995, 36, 1913-1916.
6.	S. Florio, V.Capriati, G. Colli, Tetrahedron, 1997, 53, 5839-5846.
Povzetek
Reakcije N-amino-2-benzilbenzotiazolijevih soli z aromatskimi aldehidi vodijo do razširitve obroča pri čemer nastanejo ustrezni benzotiadiazini ali benzotiazini. Substituenti na aromatskem obroču aldehida imajo zmeren vpliv na reaktivnost.