Ringöffnungen von sterisch gehinderten spirocyclischen 2,5-Dihydro- 1,3,4-thiadiazolen mit cycloaliphatischen, sekundären Aminen

Abstract

Ring Opening of Sterically Crowded Spirocyclic 2,S-Dihydro-1,3,4-thiadiazoles by Cycloaliphatic Secondary Amines At room temperature, the spirocyclic 2,5-dihydro-1,3,4-thiadiazole 3 reacted with cyclic secondary amines 6 via ring opening to give N-alkylidene-hydrazones of type 7 (Scheme 2). A reaction mechanism via a base-catalyzed transformation of the dihydrothiadiazole ring to the corresponding thiolate 19 and the intermediate thioaldehyde 21 is proposed in Scheme 6. An analogous reaction occurred with the mixture of the dispiro compounds 4/5 and morpholine (6a) or azetidine (6d), leading to a mixture of isomeric dihydrazones 8 and 9 (Scheme 3).The structure of the 'symmetrical' isomer 8a was established by X-ray crystallography. In addition to 8a and 9a, the thiirane 10a (Scheme 3 ) was isolated as a minor product.