Synthesis,oxidation and dehydrogenation of cyclic N,O‐ and N,S‐Acetals. II . Transformation of N,S‐acetals: 3‐Acylbenzothiazolines and ‐thiazolidines

The dehydrogenations with iron(III) chloride, potassium permanganate, and for the first time, CAN, tris‐[trinitrato‐cerium(IV)]‐paraperiodate (TTNCPP), and (diacetoxyiodo)benzene (IBDA) are investigated. Hydrogen peroxide, sodium periodate, potassium permanganate, and ammonium cerium(IV) nitrate (CAN) oxidation of chiral benzothiazolines, O‐ and O,N‐acylated derivatives of the condensates of D‐galactose with 2‐aminothiophenols or L‐cysteine, are also reported.     

Synthesis,oxidation and dehydrogenation of cyclic N,O‐ and N,S‐acetals. Part III. Transformation of N,O‐acetals: 3‐acyl‐1,3,4‐oxadiazolines

Various aldehyde and ketone acylhydrazones are synthesized and, under acylating conditions, cyclized into 3‐acyl‐1,3,4‐oxadiazolines. The scope and limitations of these cyclizations and the possible side reactions (e.g. formation of the open‐chain N,O‐acylhydrazinocarbinols) are dissected. For the first time, simple, convenient and efficient dehydrogenations of 3‐acyl‐1,3,4‐oxadiazolines to oxadiazoles by treatment with potassium permanganate, or more conveniently, with ammonium cerium(IV) nitrate (CAN) are presented. CAN oxidation of 2,2‐disubstituted 3‐acyl‐1,3,4‐oxadiazolines, as well as that of aldehyde diacylhydrazones (open‐chain isomers of 2,5‐disubstituted 3‐acyl‐1,3,4‐oxadiazolines) regenerates the parent carbonyl compounds.