Regioselectivity episulfonium ions

An intramolecular regioselective sulfenocyclization of unsaturated ureas 447 resulted in formation of 5,6-dihydro-4//-l,3-oxazine derivatives 449 (Scheme 86). The procedure employed phenylsulfenyl chloride and ethyldiisopro-pylamine to generate an episulfonium ion intermediate 448, from which the cyclic products 449 were formed by internal nucleophilic displacement <1995M609>. 

Azasulfenylation of alkenesf s The adducts of dimethyl(methylthio)-sulfonium tetrafluoroborate (1) with alkenes react slowly but smoothly with various nitrogen nucleophiles to give products of overall rrarw-addition to the alkene. Regioselectivity depends on the substitution pattern of the alkene and on the nucleophilicity of the attacking reagent, and is subject to some control. The mechanism of this azasulfenylation is not certain it may involve an episulfonium ion. 

---