Protecting-Group-Free Synthesis of 1‑Phenylisoquinolin-4-ols: Thermal Cyclization of Methyl 2‑[(Diphenylmethylidene)amino]acetates

A protecting-group-free synthetic approach to 1-phenylisoquinolin-4-ols was developed by the intramolecular thermal cyclization of methyl 2-[(diphenylmethylidene)­amino]­acetates. R¹ and R² substituents were found to affect the required reaction temperatures, time, and yields of the cyclized products. The reactivity of the Schiff bases increased upon introduction of α-benzoyl and α-ester groups (R²). The cyclization yield also depended on the position of the R¹ substituents on the phenyl groups