Investigations in the field of synthetic dyes

Synthesis of 3‐Aminopyrido[2,1‐a]isoquinolin‐4‐one Derivatives via Condensation of Azlactones with 1‐Alkyl‐3,4‐dihydroisoquinolines

“…The reaction of 4‐(ethoxymethylene)‐2‐phenyloxazol‐5(4 H )‐one 5 with 6,7‐dimethoxy‐1,3,3‐trimethyl‐3,4‐dihydroisoquinoline 18 a upon heating in MeCN for 2 h led to the condensation of these compounds with the formation of a conjugate 23a (Scheme 1), which has a burgundy color and high molar extinction coefficient ϵ EtOH =52.0⋅10 3 M −1 cm −1 (λ=550 nm) and ϵ EtOH =60.6⋅10 3 M −1 cm −1 (λ=519 nm). The formation of conjugated compounds similar to cyanine dyes as a result of the reaction of azlactones with CH‐acids has been reported earlier [27a–e] …”