α-Substitution of β-Thienylcarbamates: Alkylation, Vinylation and Pd-Catalyzed Coupling Reactions

Reaction of the trilithio derivative of di-t-butyl thiophene-3,4-diyldicarbamate 4 with alkyl halides has led to 2-alkylthiophenedicarbamates 9 and 11 and 4-alkylthieno[3,4–d]imidazolones 12. Acid catalyzed α-alkylation of 4, using α-branched or functionalized aldehydes, has allowed the synthesis of divinylthiophenes 13 and thieno[3,2–b]pyridines 14–16, respectively. Pd-catalyzed coupling reactions involving halo- or dihalothienylcarbamates 10, 17, 18 were studied. One or two alkenyl, alkynyl, aryl groups were introduced on the thiophene nucleus.