Bong Ser Park

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.

Reversed diastereoselectivity in the Yang photocyclization upon introducing a cyclopropyl group at the alpha position to carbonyls

Abstract 1-Benzoy1-1-( o -ethylphenyl)cyclopropane favors the E -indanol formation in its photochemical reaction and the selectivity is maximized in methanol. These are exactly opposite to the photochemical behavior of α-( ortho -ethylphenyl)acetophenone. Our computational studies suggest that the different stereochemical outcome of the two systems originates from the geometric difference of initially formed biradical intermediates.

PHOTODECARBONYLATION OF 2-PHENYL-4-ALKYLIDENE-5(4H)-OXAZOLONES

Abstract The title compounds were prepared by the Erlenmeyer synthesis and irradiated with or without a Pyrex filter using 450 W medium pressure mercury arc lamp. Cis-trans isomerization was the major reaction under pyrex filtered condition, whereas irradiation without a Pyrex filter resulted in decarbonylation, followed by trapping of the ketenimine intermediate by protic solvents.

2-Hydroxyphenacyl ester: a new photoremovable protecting group

A 2-hydroxyphenacyl moiety absorbing below 370 nm is proposed as a new photoremovable protecting group for carboxylates and sulfonates. Laser flash photolysis and steady-state sensitization studies show that the leaving group is released from a short-lived triplet state. In addition, DFT-based quantum chemical calculations were performed to determine the key reaction steps. We found that triplet excited state intramolecular proton transfer represents a major deactivation channel. Minor productive pathways involving the triplet anion and quinoid triplet enol intermediates have also been identified.

Photochemistry of 1-(o-tolyl)-1-benzoylcyclopropane and 2-(o-tolyl)-2-benzoyloxirane: Determination of ring opening rates of oxiranylcarbinyl radicals

Abstract Photolysis of the title compounds results in efficient hydrogen transfer reaction to produce 1,5-biradical intermediate, which does not form in the photolysis of a structurally similar compound, α-(o-tolyl)isobutyrophenone. From their kinetic studies we have measured the rearrangement rate constant of a substituted oxiranylcarbinyl radical.