β-Phenyl quenching of 9-phenylphenalenones: a novel photocyclisation reaction with biological implications.

The singlet and triplet excited states of 9-phenylphenalenones undergo β-phenyl quenching (BPQ) via addition of the carbonyl oxygen to the ortho position of the phenyl substituent. This reaction leads to the formation of naphthoxanthenes , which, in the absence of quenchers, undergo a very rapid electrocyclic ring opening reaction reverting to within a few microseconds. Naphthoxanthene contains a remarkably weak C-H bond, which enables efficient hydrogen transfer reactions to suitable acceptors, giving rise to the production of the naphthoxanthenyl radical or the naphthoxanthenium cation, depending on the solvent polarity.

N-acyldihydropyridones as synthetic intermediates. A stereoselective synthesis of acyclic amino alcohols containing multiple chiral centers.

Various multisubstituted piperidines containing a phenyl group at C-2 can be opened regio- and stereoselectively with cyanogen bromide. The ring-opened products contain useful cyanamide and benzylic bromide functional groups. The benzyl bromide can be cleanly reduced, or substituted with various nucleophiles via an S(N)2 process to add additional heteroatoms stereoselectively.

Stereoselective synthesis of acyclic amino alcohols via von Braun ring opening of chiral piperidines.

Multisubstituted piperidines containing a phenyl group at C-2 can be opened regio- and stereoselectively with cyanogen bromide. The ring-opened products contain useful cyanamide and benzylic bromide functional groups. This methodology is useful for the stereoselective synthesis of uniquely substituted alkylamine derivatives containing multiple chiral centers and various functionality.

Phototoxic phytoalexins. Processes that compete with the photosensitized production of singlet oxygen by 9-phenylphenalenones.

Experiments were performed to elucidate the excited-state behavior of 9-phenylphenalenones, which are phototoxic plant secondary metabolites involved in mechanisms of light-mediated plant defense. Using a combination of time-resolved and steady-state UV/visible spectroscopies, time-resolved IR absorption spectroscopy, time-resolved singlet oxygen phosphorescence measurements and cyclic voltammetry, we provide evidence of an intramolecular charge-transfer process in the excited singlet and the triplet states of 9-phenylphenalenones that modulates the photosensitized production of singlet oxygen.

Light- and singlet oxygen-mediated antifungal activity of phenylphenalenone phytoalexins.

The light-induced singlet oxygen production and antifungal activity of phenylphenalenone phytoalexins isolated from infected banana plants (Musa acuminata) are reported. Upon absorption of light energy all studied phenylphenalenones sensitise the production of singlet oxygen in polar and non-polar media. Antifungal activity of these compounds towards Fusarium oxysporum is enhanced in the presence of light.

A novel free-radical ring contraction of a cyclic carbamate.

During a study on iodocyclocarbamation reactions of 2-styryl-4-piperidones, a novel ring contraction was observed. Iodocyclocarbamation of 2-styryl-4-piperidone 3 gave the bicyclic carbamate 4. Reduction of 4 under free-radical conditions effected a stereoselective ring contraction to provide oxazolidinone 6.