CONDENSED HETEROCYCLICS .28. SYNTHESIS OF SUBSTITUTED NAPHTHO[1,2-B]THIAPYRANO[3,4-B]QUINOXALINE AND ITS 8-AZA ANALOGS

6, 6-Dimethyl-6H-naphtho[1, 2-b]thiapyrano[3, 4-b]quinoxaline (4), 6, 6, 9-trimethyl-6H-naphtho[1, 2-b]thiapyrano[3, 4-b]quinoxaline (5a), 6 , 6, 9, 10-tetramethyl-6H-naphtho[1, 2-b]thiapyrano[3, 4-b]quinoxaline (6a), 9-chloro-6, 6-dimethyl-6H-naphtho[1, 2-b]thiapyrano[3, 4-b]quin oxaline (7a) and 9-bromo-6, 6-dimethyl-6H-naphtho[1,2-b]thiapyrano[3, 4-b]pyrido[2, 3-e]pyrazine (8a) have been synthesized by reacting appr opriate diamines with 2, 3-dihydro-2, 2-dimethyl-4H-naphtho[1, 2-b]thi apyran-3, 4-dione (3). The orientation of cyclisation has been establi shed by NMR spectral analysis and analogy. It has been observed that s teric hinderance predominated over reactivities in directing the cours e of cyclodehydration reactions.