Silica gel-mediated chemical degradation of dimeric pyranonaphthoquinones into their monomeric units

We present herein the chemical degradation of dimethyl uroleuconaphins A(2) and B-2 mediated by silica gel. The reaction promoted carbon-carbon bond cleavage of the dimeric structure, resulting in the monomeric units. We optimized the degradation conditions by screening the promoters and solvents, revealing that the use of silica gel in MeOH was effective. The monomeric pyranonaphthoquinones were also produced by a redox conversion. In addition, the pH chromism of the monomer as a photophysical property was evaluated.