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The scope of the acid-catalyzed cyclodehydration of 2-(p -hydroxyalky1)carboxylic acid hydrazides into 5,6-dihydro-4H-l, 3,4-oxadiazines has been extended through the use of acidic reagents other than concentrated sulfuric and polyphosphoric acids. Additional data are presented which corroborate previously proposed mechanisms of this reaction.We have reported (2) on the scope of the concentrated sulfuric acid cyclodehydration of certain 2-(0-hydroxyalky1)carboxylic acid hydrazides into 5, Gdihydro -4H -1 , 3 , 4oxadiazines and proposed two alternative mechanisms for the formation of trans isomers in concentrated sulfuric acid and a mechanism for the formation of cis isomers in polyphosphoric acid. This paper describes the use of other reagents to extend the scope of this reaction. It presents data which allow us to select the preferred mechanism of the two alternatives proposed for the concentrated sulfuric acid formation of trans isomers. These data also corroborate the mechanism proposed for the formation of cis isomers in polyphosphoric acid.

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