(Z)-5-Benzylidene-2,5-dihydro-4-hydroxy-3-thiophenecarboxanilides: Synthesis and Isomerization into 5-Benzyl-4-hydroxy-3-thiophenecarboxanilides

Article abstract of DOI:10.1002/hlca.19800630623

Upon treatment with an arylamine in boiling xylene, the esters I yield predominantly the corresponding anilides II, along with a small but variable amount of the isomeric thiophene derivatives III (Table I).On the other hand, the derivatives III can be readily prepared by base- or acid-catalyzed isomerization of II.Esters I can also be isomerized to the corresponding thiophene derivatives IV (Scheme 6), but only in the presence of a strong acid (Table 4).The two series of isomers reported in Tables 2 and 3 present spectral differences which allow unambiguous structural assignments.The (Z)-configuration for compounds of Table 2 is confirmed by a NOE study carried out on the O-methyl derivatives 6a and 7a.