Synthesis, characterization and biological activity of some new dihydroisoquinolines and dihydrothieno [2,3-c]isoquinolines

In this work, a versatile compound, 4-cyano-1,6-dimethyl-8-phenyl-7,8-dihydroisoquinoline-3(2H)-thione (3) was synthesized and utilized as a starting compound for the preparaton of the title compounds.Thus, reaction of 3 with iodomethane, 2-chloroacetamide, ethyl chloroacetate, chloroacetonitrile or N-(benzthiazol-2-yl)-2chloroacetamide by heating in ethanol containing sodium acetate, gave 3-unsubstituted or 3-substituted methylsulfanyl-7,8-dihydroisoquinoline-4-carbonitriles 4 or 6, 8, 10 and 16 respectively.The latter compounds (6, 8, 10 and 16) contain an active methylene group that adds easily to the carbonitrile group to build a thiophene ring, fused to an isoquinoline moiety, upon heating with sodium ethoxide in ethanol thus affording the corresponding 6,7-dihydrothieno[2,3-c]isoquinolines 7, 9, 11 and 17, in nearly quantitative yields.Compounds 9, 11 and 17 underwent further reactions with some reagents to give other 6,7dihydrothieno[2,3-c]isoquinolines 12-15 and 3,4-dihydropyrimidothienoisoquinoline 18.All synthesized compounds were screened for their biological activity as bactericidal and fungicidal agents.Some of them showed promising antifungal activity.