Photocyclization of benzofurancarboxanilides. Photorearrangement of the benzodihydrofuran system to 3-o-hydroxyphenylquinolones

$\text{cis}$-Dihydrobenzofuro2,3-c]quinolone ($\text{4a}$) and $\text{cis}$-dihydrobenzofuro-3,2-c]quinolone ($\text{5}$) undergo photorearrangement, characteristic to the benzodihydrofuran system, leading to 3-$\text{o}$-hydroxyphenylquinolone ($\text{6}$). A plausible mechanism involving a cyclopropyl dienone ($\text{12}$) was discussed.