Synthesis of 1,1,3‐Trisubstituted Naphtho[2,3‐c]pyran‐5,10‐dione Derivatives as Potential Redox Switches

Five 1,1,3‐trisubstituted naphtho[2,3‐c]pyran‐5,10‐dione derivatives were designed and synthesized in five steps from 2‐acetyl‐1,3‐indandione. Prepared quinones 6a–e instantly changed from either red or blue to yellow or orange red, when treated with sodium borohydride in methanol. The resulting reduced hydroquinones 9a–e reverted to their original colors within a few minutes after the reducing agent was consumed or removed. Whereas no fluorescence of blue quinone 6e was detected prior to reduction, reduced hydroquinone 9e emitted red fluorescence with a quantum yield of 0.07.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)