SYNTHESIS AND NMR-SPECTRA OF THE 6 ISOMERIC THIENO[C]-FUSED 1,7-NAPHTHYRIDINES AND 1,8-NAPHTHYRIDINES

Through the use of Pd(0)-catalyzed coupling between 2- and 4-formyl-3-thiopheneboronic acid and 4-iodo-3-aminopyridine (1) and 3-bromo-2-aminopyridine, convenient one-pot procedures for the preparation of thieno[2,3-c]-1,7-naphthyridine (2), thieno[3,4-c]-1,7-naphthyridine (3), thieno[2,3-c]-1,8-naphthyridine (6) and thieno[3,4-c]-1,8-naphthyridine (7) have been developed. Thieno[3,2-c]-1,7-naphthyridine (4) and thieno[3,2-c]-1,8-naphthyridine (8) were obtained through the coupling of 2-tri-n-butylstannyl-3-thiophenaldehyde with 2,2-dimethyl-N-(4-iodo-3-pyridinyl)propanamide and 3-bromo-2-acetamidopyridine (1). The yield of 8 was further increased when copper(II) oxide was used as the co-reagent. The C-13 nmr spectra of the six isomeric thieno[c]-fused 1,7- and 1,6-naphthyridines are discussed.