A convenient and clean “on water”-mediated synthesis of benzothiazoles/benzothiazolines is reported. Aromatic, heteroaromatic, and styryl aldehydes are converted to 2-substituted benzothiazoles in high yields in a one-pot reaction with 2-aminothiophenol in water at 110 °C (oil-bath). Alkyl and aryl alkyl aldehydes afforded the benzothiazolines. The reaction is highly chemoselective with no competitive thia-Michael addition, O-dealkylation/debenzoylation, reduction of the nitro or the α,β-unsaturated carbonyl groups, and substitution of the halogen atom or the nitro group. The reaction is found to be general with respect to the 2-aminothiophenol substrate through the reaction of a few substituted 2-aminothiophenols with a few representative aromatic and aliphatic aldehydes. The procedure does not involve the use of any additional reagent/catalyst, produces no waste, and represents a green synthetic protocol.

Carboxylic acids are converted to benzothiazoles by ­direct condensation with 2-aminothiophenol under microwave irradiation in the absence of solvent.

Phenolic esters are efficiently converted to 2-substituted benzothiazoles in a one-pot reaction by treatment with 2-aminothiophenol in the presence of a catalytic amount of K₂CO₃ in N-methyl-2-pyrrolidone (NMP) at 100 °C.