Science of Synthesis

Schatz, J., Science of Synthesis, (2001) 9, 312.

Ketene dithioacetals ‌82‌ bearing an active methylene group are readily deprotonated using sodium hydride as base. The anion formed can be trapped with isothiocyanates ‌83‌. Intramolecular Michael addition of the thiolate intermediate ‌84‌ followed by elimination of a methylsulfanyl group yields tetrasubstituted thiophenes ‌85‌ (‌Scheme 35‌). The overall process can be regarded as a stepwise anionic [3 + 2]-cycloaddition reaction of a propenide anion to a thiocarbonyl bond.[‌334‌]

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