Herein, BF3·Et2O-promoted
O-insertion/spirocyclization/fluorination/ring-expansion
of unsaturated amides to synthesis of spiro[benzo[b]-[1,4]dioxepine-3,5′-oxazole]
skeletons in the presence of natural light and O2 (3Σg–) was reported. Air
was the oxygen source of the 1O2-generation
and O-insertion reaction under metal-free and mild conditions. BF3·Et2O played multiple roles, such as Lewis
acid, activating reagent, and fluorine source in the reported cascade.
A mechanism involving 1O2 generation/activation
of double bond/O-insertion/spirocyclization/fluorination/ring expansion
was supposed.