DAST-mediated Beckmann Rearrangement-cyclizations Of Oximes

The Beckmann rearrangement, isomerization of oximes to amides, is a vital reaction forpreparing Nylon6in industy. Oxime derivatives, as valuable insecticide and antibiotic, haveextensive use in agriculture as well as in pharmacology.The synthesis of oximes and its applications have been intensively investigated since itsappearance. Oxime derivatives are easily to prepare and have divers synthetic sites, whereinthey have emerged as versatile synthetic compounds in organic chemistry, especially inprotection/deprotection of carbonyl, formation of amides, nitriles, asymmetric synthesis ofamines and heterocycles containing nitrogen atom. Recently, the rising attention focus on theamination reaction as well as coupling reaction catalyzed by transition-metal of oximes.As an efficient nucleophilic fluorination agent, Diethylaminosulfur trifluoride(DAST),can effectively activate hydroxyl and carbonyl group, resulting in C-O bond cleavage.Meanwhile, the hydroxyl of oximes can be activated by DAST. Methods were reported tohighly functionalized pyrazole and isoxazole from cyclopropyl oximes, which reprent astructure-special class of oximes. Based upon these previous works, this thesis mainylconcern their new reactivity mediated by DAST.1. A series of highly substituted2-oxazolines were synthesized regioselectively fromα-alkylamino carbonyl oximes via a Beckmann rearrangement/cyclization process mediatedby DAST.2. Benzimidazole and benzimidazole derivatives were obtained from1-2-(amino)phenyl)ethanone oxime mediated by DAST.In conclusion, an efficient method for preparation of spiro-fused2-oxazolines has beendeveloped through DAST-mediated Beckmann rearrangement/cyclization reactions. Themethod is under mild condition and easily available material. It’s noteworthy that the methodcan also be used for synthesis benzimidazoles and benzimidazoles, thus imply that thisprotocol may be capable of other appropriate substrates.