Condensation of Thioamides with 2-Aminothiophenols: A Versatile Synthesis of Benzothiazoles

References

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• For instance, condensation of phenoxy acetic acid or its ethyl ester with 5-methyl-2-aminothiophenol under a variety of acids (H2SO4, PPA or P2O5 - CH3SO3H) gave none of the expected 2-phenoxymethyl-6-methyl benzothiazole (Product 19), where as with phenoxy acetyl chloride in NMP solvent, only 15% yield of this compound was obtained after chromatograptic seperation. Also, 2-benzoxymethyl-6-methyl benzothiazole (Product 20) was not accessible by attempted reaction of benzoxy acetic acid or its ethyl ester with 5-methyl-2-aminothiophenol
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• Substrates, 2-aminothiophenols and thioamides are all known compounds and were prepared by literature methods. In cases where benzothiazole products are new, mp, ir and 1H-nmr spectral data are given below: Product 16: m.p. 76—78°C (from Petroleum ether 60—80°C); ir (KBr) 1740, 1600, 1530, 1450, 1350, 1260, 1190 and 870cm−1; nmr (CDCl3), δ 5.65 (2H,S) 7.2—8.2 (9H,m). Product 19: m.p. 106—108°C (from petroleum ether-ethyl acetate); ir (KBr) 1600, 1530, 1440, 1360, 1250, 1170, 1060, 820cm−1; nmr (CDCl3), δ 2.50 (3H,S), 5.45 (2H,S), 6.8—7.8 (8H,m). Product 20: m.p. 77—78°C (from Petroleum ether 60—80°C); ir (KBr) 1720, 1600, 1450, 1350, 1270, 1110, 810cm−1; nmr (CDCl3), δ 2.95 (3H,S), 5.60 (2H,S), 7.0—8.0 (8H,m). Product 23: m.p. 110—112°C (from alcohol); ir (KBr) 1730, 1590, 1510, 1440, 1360, 1240, 1190, 820, 765cm−1; nmr (CDCl3) δ 1.2 (3H,t,J=7Hz), 4.25 (2H,q,J = 7Hz), 4.0 (2H,S), 7.2—8.2 (3H,m). Product 25: m.p. 215—217°C (from aq.alcohol); ir (KBR) 3000, 1720, 1600, 1520, 1500, 1370, 1330, 1250, 1200, 1070, 900cm−1; nmr (CDCl3-DMSO) δ 3.8 (1H,bs), 5.4 (2H,s), 7.0—8.0 (8H,m)
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