Ketonic hydrolysis of 7‐acetyl‐4‐cyano‐1,6‐dimethyl‐6‐hydroxy‐8‐phenyl‐5,6,7,8‐tetrahydro‐isoquinoline‐3(2H)‐thione (1) via heating with aqueous solution of potassium hydroxide resulted in both deacetylation and dehydration affording new 7,8‐dihydroisoquinoline scaffold (7,8‐DHISQ) 2. Two simple mechanistic approaches are postulated for this synthesis. One of them was supported by converting 7‐acetyl‐4‐cyano‐1,6‐dimethyl‐8‐phenyl‐7,8‐dihydroisoquinoline‐3(2H)‐thione (3) into 7,8‐DHISQ 2 via heating with aqueous solution of potassium hydroxide. Compound 2 was used as a key intetermediate for synthesizing other 7,8‐DHISQ's 4 and 6, as well as 7,8‐dihydrothienoisoquinoline 7. Reaction of compound 3 with 2‐chloroacetamide (8) by refluxing in ethanol containing sodium acetate gave 7‐acetyl‐1‐amino‐5,8‐dimethyl‐6‐phenyl‐6,7‐dihydrothieno[2,3‐c] isoquinoline‐2‐carboxamide (10) which