Highly efficient green synthesis of the photochromic spironaphthoxazines using an eco-friendly choline hydroxide catalyst

A greener route for the synthesis of the photochromic spironaphthoxazines employing a highly efficient, biodegradable and recyclable choline hydroxide catalyst in an aqueous medium has been described. This methodology offers diverse advantages such as mild reaction conditions, short reaction time (1 h), excellent yields (up to 91%), and operational simplicity that make it a useful and attractive option for the synthesis of the spironaphthoxazines. The choline hydroxide showed excellent catalytic performance until five recycles without significant loss of activity. The structures of synthesized spironaphthoxazines were deduced by their H-1 NMR spectra and melting points.