A Simple Approach to the One-Pot Three Component Synthesis of 4Hpyrimido [2,1-b] benzothiazole Derivatives Using Polyethylene Glycol (PEG-400)

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.