Poly(ethylene glycol) (PEG) as an efficient and recyclable reaction medium for the synthesis of dibenz[b,f]-1,4-oxazepine

Poly(ethylene glycol) (PEG) has been used as a sustainable, non-volatile, and environmentally friendly reaction solvent for the synthesis of dibenz[b,f]-1,4-oxazepine (2a). PEG-400 as a promoter provided 89% of 2a within 8 h. We compared the reactivity of PEG-400 with 18-crown-6, tetra-n-butylammonium bromide and ionic liquids as phase transfer catalysts. Further, we investigated our protocol with various PEGs, with molecular weight 200, 300, 1000, 2000, 8000, 10,000, and 20,000. The reaction provided excellent yields with low as well as high molecular weight PEGs. We also studied the effect of various organic cosolvents (polar protic/aprotic/non-polar) on the reactivity of PEG-400 for the synthesis of 2a.