Substituent Effects on [1,3]-Rearrangement of Alkynyl S,N-Acetals to 1- Amino-3-Sulfenylallenes and their Conversion to α,β-Unsaturated Ketones

The reaction of thioiminium salts derived from aromatic thioamides with lithium phenylacetylide exclusively gave S,N-acetals, whereas the reaction with lithium (trimethylsilyl)acetylide gave 1-amino-3- sulfenylallenes via [1,3]-rearrangement. The easiness of [1,3]-rearrangement was highly dependent on the substituents at the nitrogen atom. Chromatographic purification of the reaction mixture produced α,β- unsaturated ketones.