[Tetracyclic derivatives of diltiazem from aurones and thioaurones]

Tetracyclic derivatives of diltiazem from aurones and thioaurones Heating the aurones 1a, b and the thioaurones 1c, d with 2-aminothiophenol in polyphosphoric acid (PPA) under nitrogen yields the 6,12-dihydrobenzofuro[2,3-c][1,5]benzothiazepines 3a,b and the sulfur analogues 3c, d, respectively. Reaction of the annulated benzofuranes 3a,b with 2-chloroethyl-N,N-dimethylammonium chloride and potassium carbonate leads to S-alkylation and ring opening forming the 3-imino-aurones 5. The tetracycles 3 react with sodium hydride in DMF under ring contraction to afford the benzofuro- and benzothieno[3,2-b]quinolines 6. The stability of the partially saturated tetracycles 3 is investigated by anodic oxidation using the rotating platinum electrode by means of differential pulse voltammetry. The measured half wave potentials of the 1,4-dihydropyridine partial structure in compounds 3 are compared with that of nifedipine.