PEG-400 was found to be an inexpensive, non-toxic and eco-friendly reaction medium for synthesis of pyramido[2,1-b]benzothiazole derivatives. Utilizing this protocol, we are capable of various pyrimido[2,1-b]benzothiazole derivatives
4a-k and 6a-d were synthesised. The reaction between aminobenzothiazole 1, aromatic aldehydes 2a-k and ethyl
acetoacetate 3/ diethyl malonate 5 at room temperature for 1-2 h furnished required compounds with good to excellent
yields (85-93%). Here we observed carboxylic acid compounds instead of ester compounds when diethyl malonate was
used as the substrate, whereas ethyl acetoacetate showed no signs. The reactions are easy to perform, atom-economic, require
less reaction time and allow generation of the biologically potent pyrimido[2,1-b]benzothiazole frameworks from
readily accessible starting materials.