1. For reviews on 1,3-thiazine chemistry, see: (a) Mironova, G. A.; Kuklin, V. N.; Kirillova, Ye. N.; Ivin, B. A. Chem. Heterocycl. Compd. (Engl. Transl.) 1986, 22, 1–13;
2. (b) Quiniou, H.; Guilloton, O. Adv. Heterocycl. Chem. 1990, 50, 85–156;
3. (c) Ryabukhin, Yu. I.; Korzhavina, O. B.; Suzdalev, K. F. Adv. Heterocycl. Chem. 1996, 66, 131–191.
4. Ziegler, E.; Steiner, E. Monatsh. Chem. 1964, 95, 495–500. The authors described the synthesis of compound 1a starting from xantogenamid, malonic acid and PCl3. They reported an mp of 184°C for this product. We have repeated this reaction and obtained the product with mp 198–200°C, which has exactly the same spectral characteristics as 1a obtained by our method: 1H NMR (CDCl3, 500 MHz) δ 17.67 (s, 1H), 8.43 (br s, 1H), 2.69 (s, 3H); 13C NMR (DMSO-d6, 125 MHz) δ 198.4, 180.3, 173.4, 163.2, 101.2, 26.8; MS (70 eV): m/e 187 (M+, 28%), 127 (28), 99 (30), 84 (22), 69 (25), 43 (100).
5. Selected spectroscopic data: 4-Hydroxy-5-(1-phenyliminoethyl)-3,6-dihydro-2H-1,3-thiazine-2,6-dione, 2a. Mp 244–245°C. 1H NMR (DMSO-d6, 500 MHz) δ 14.14 (s, 1H), 11.87 (s, 1H), 7.38–7.54 (m, 5H), 2.47 (s, 3H); 13C NMR (DMSO-d6, 125 MHz) δ 180.6, 173.4, 168.4, 163.0, 135.7, 129.5, 128.3, 125.9, 97.6, 20.7; MS (70 eV): m/e 262 (M+, 100%), 234 (15), 201 (23), 163 (27), 158 (65), 130 (69), 118 (42), 77 (100), 67 (38), 51 (54), 39 (42).5-(1-Benzyliminoethyl-4-hydroxy-3,6-dihydro-2H-1,3-thiazine-2,6-dione, 2b. Mp 187–188°C. 1H NMR (CDCl3, 500 MHz) δ 12.93 (br s, 1H), 8.62 (s, 1H), 7.26–7.41 (m, 5H), 4.67 (d, 2H, J=5 Hz), 2.64 (s, 3H); 1H NMR (DMSO-d6, 500 MHz) δ 12.88 (br s, 1H), 11.40 (s, 1H), 7.32–7.40 (m, 5H), 4.69 (d, 2H, J=5 Hz), 2.58 (s, 3H); 13C NMR (DMSO-d6, 125 MHz) δ 180.1, 174.1, 167.7, 163.1, 135.8, 128.9, 127.9, 127.5, 96.9, 47.3, 18.8; MS (70 eV): m/e 276 (M+, 45%), 187 (25), 144 (35), 91 (100), 65 (27), 39 (15).