An important method for a-functionalization of thiophenes is lithiation followed by treatment with an electrophile.'When a coordinating substituent (ie,(dimethy1amino) methyl) is present in position 3, lithiation is directed to the 2-p0sition,~ whereas noncoordinating sterically bulky substituents in position 3 (Le., tert-butyl) lead exclusively to 5-lithiati0n.~ When the coordinating ability of a 3-substituent does not fully compensate for steric effects, lithiation ...
