Synthesis of substituted pyrido-oxazepine-3-ols and benzo-oxazin-2-yl methanol via tandem epoxide opening and SNAr reaction

Abstract

A general and catalyst-free protocol for the synthesis of pyrido-oxazepine-3-ols and benzo-oxazin-2-yl methanol via tandem epoxide opening followed by SNAr reactions is reported. Oxirane derived from tribromopyridine undergoes epoxide opening followed by the SNAr reaction, yielding seven-membered pyrido-oxazepine-3-ols. Predominantly 2-cyclized pyrido-oxazepine-3-ols observed in this reaction. Oxirane derived from tribromonitrobenzene undergoes epoxide opening followed by SNAr reaction to produce six-membered benzo-oxazin-2-yl methanol. When oxirane treated with primary amine, mainly 2-cyclized benzo-oxazin-2-yl methanol is formed. furthermore, treatment of oxirane with secondary amine result in regio-selective 4-cyclized benzo-oxazin-2-yl methanol, accompanied by de-alkylation. A plausible reaction mechanism is proposed for the synthesis of benzo-oxazin-2-yl methanol, which proceeds via epoxide opening followed by a Smiles rearrangement.