The Use of an Unusual Rearrangement Sequence for the Syntheses of 3‐(1‐Aminoalkylidene)‐3H‐thiophen‐2‐ones and two Examples of their Surprising Electrophilic‐Induced Dimerization Reactions

The reaction of 2‐amino‐3‐carbomethoxythiophene ( 1a ) and 2‐amino‐3‐carboethoxy‐4,5‐dimethylthiophene ( 1b ) with methyl‐ or ethylmagnesium chloride leads to new 3‐(1‐aminoalkylidene)‐3H‐thiophen‐2‐ones 4a—d in good yields (60—87%). Treatment of the compounds 4a and 4c with catalytic amounts of p‐TsOH in boiling CHCl₃ afforded the (±)‐4,4′‐bis‐(1‐aminoalkylidene)‐3′,4′‐4H,2′H‐2,3′]bithiophenyl‐5,5′‐diones 9a and 9b as new interesting heterocycles in preparatively useful yields (60/mdash;65%).