Synthesis and properties of 1,6-methano[10]annuleno[3,4-c]thiophene and its 1,3-dicyano derivative

New thiophene-annulated 1,6-methano[10]annulene 1 and 2 were synthesized. The anisotropic deshielding effect from the π-electron system, based on the chemical shift values of the bridged methylene protons, is reduced compared with that of 3, and their crystal structures show clear bond alternation.