The Power of Solvent in Altering the Course of Photorearrangements

A clean bifurcation between two important photochemical reactions
through competition of a triplet state Type II H-abstraction reaction
with a photo-Favorskii rearrangement for (o/p)-hydroxy-o-methylphenacyl esters that
depends on the water content of the solvent has been established.
The switch from the anhydrous Type II pathway that yields indanones
to the aqueous-dependent pathway producing benzofuranones occurs abruptly
at low water concentrations (∼8%). The surprisingly clean yields
suggest that such reactions are synthetically promising.