Novel Methods for the Synthesis of 5-Substituted-3-carboxy-2,5- and 4,5-Dihydrothiophenes and 5-Substituted 2- and 3-Sulfolenes.

Various approaches to the syntheses of 5-substituted-3-carbomethoxy-2,5-dihydrothiophenes and their product sulfolenes, required as synthetic precursors for tangutorine, are described. An efficient route to 3,5-disubstituted-4,5-dihydrothiophenes and hence 3,5-disubstituted-2-sulfolenes by radical chemistry is also described.