Benzylidène-5-hydroxy-4-dihydro-2,5-thiophènecarboxanilides-3-(Z): Synthèse et isomérisation en benzyl-5-hydroxy-4-thiophènecarboxanilides-3

(Z)-5-Benzylidene-2,5-dihydro-4-hydroxy-3-thiophenecarboxanilides: Synthesis and Isomerization into 5-Benzyl-4-hydroxy-3-thiophenecarboxanilides 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 1). 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 .