A rapid, metal-free synthesis of amino- and hydroxyphenanthrenes with tunable photophysical properties

Here we report a general, metal-free strategy for the regioselective synthesis of amino- and hydroxyphenanthrenes from 1- and 2-naphthaldehydes. The sequence employs an E-selective Wittig olefination, followed by a regioselective Houben–Hoesch annulation, enabling access to 1- and 4-substituted amino- and hydroxyphenanthrenes in moderate yields. The method tolerates diverse substitution patterns and proceeds without the need for precious metal catalysts or elaborate precursors. Substituents introduced via this approach significantly modulate the absorption and emission properties of the resulting phenanthrenes, underscoring the utility of the method for generating phenanthrene-based materials with tunable photophysical behavior.