Thieno[3,4-b]pyrazines: synthesis, structure, and reactivity.

A general synthetic route has been developed for the efficient preparation of 2,3-disubstituted thieno[3,4-b]pyrazines. These methods eliminate problems in the preparation of the precursor 3,4-diaminothiophene and utilize alpha-diones prepared through the reaction of the appropriate organocuprates with oxalyl chloride. This combination allows the convenient preparation of thieno[3,4-b]pyrazine and its 2,3-disubstituted analogues (where substituent = methyl, hexyl, octyl, decyl, dodecyl, and phenyl) in high yield. Characterization of the structure and reactivity of this class of compounds is also described, including the results of structural, electrochemical, and pK(a) studies.