AbstractCyclisation of 2‐methyl‐3‐phenyl‐but‐3‐en‐anilide (III) with polyphosphoric acid gavecis‐3, 4‐dimethyl‐4‐phenyl‐3, 4‐dihydro‐carbostyril (VII) in 61% yield together with a small amount of 2, 3‐dimethylindenone (VIII), whereas with AlCl3a phenyl group was split off to give 3, 4‐dimethylcarbostyril (VI). The anilide III isomerises tocis‐ andtrans‐2, 3‐dimethyl‐cinnam‐anilide (IV resp. V) under basic conditions.The anilides IV and V gave only small yields of the dihydrocarbostyril VII with polyphosphoric acid. Chlorination of VII in position 3 using PCl5yielded IX which, on splitting out HCl, gave 3‐methylene‐4‐methyl‐4‐phenyl‐3, 4‐dihydro‐carbostyril (X). X was converted totrans‐3, 4‐dimethyl‐4