Amidinium salts rearrangement

A somewhat similar isomerization was observed with the sultam 5-methylimino-4-phenyl-l,3,4-dithiazolidine 1-dioxide (17 i = H). On heating at 60°C in the presence of benzoyl chloride, rearrangement into the isomeric 5-phenylimino-4-methyl-l,3,4-dithiazolidine 1-dioxide (19, 1 = H) was found (Scheme IV.ll). As intermediate can be proposed the amidinium salt 18 (78JOC4951). Furthermore, NMR-controlled test tube experiments revealed that this rearrangement also occurs under influence of aluminum trichloride and methanesulfonyl chloride. Also, the 2-phenyl derivative 17 (R = CeHs) could be isomerized it required heating in acetone with m-dichlorobenzoic acid as catalyst (Scheme IV.ll). 

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