Hong-Son Ryang

Photodecomposition of acetoins

The photodecomposition of α-substituted acetoins (la–e), both by direct irradiation and by α-diketone sensitization, has been studied. Direct irradiation at 313 nm gives acetyl derivatives (2a–e) in good yield. The reactions are not quenched by triplet quenchers. Quantum yields for the formation of 2-acetyl-1-methylpylpyrrole (2a) are low relative to those for acetophenone (2e) and markedly decrease as solvent polarity increases. α-Diketones such as biacetyl and benzil photosensitize the decomposition of acetoins (1a–d) to (2a–d), and are thereby converted into reduction products. The decomposition of α-phenylacetoin (1e) is not sensitized by the α-diketones. The sensitized decomposition of acetoins (1a–d) can be completely quenched by triplet quenchers. Quantum yields for disapperance of biacetyl in the reaction with (1a) and rate constants for biacetyl phosphorescence quenching by (1a) are both enhanced on going from benzene to acetonitrile as solvent. Mechanisms are discussed on the basis of kinetic and deuterium-labelling experiments.

Photochemical dimerization of benzofuran derivatives

The photochemical reaction of benzofuran with 2-(1-pyridyl)benzofuran (1) results in the formation of cross-dimers (3) and (4); an excited singlet of benzofuran is implicated as the reactive excited state.

Biacetyl photosensitized decomposition of acetoin derivatives

Biacetyl photosensitizes the decomposition of the acetion derivative (1a) to give (3a) and reduction products of biactyl quantitatively; kinetic data suggest that the reaction occurs via charge-transfer interaction derived from n-π* triplet of biacetyl.

Preparation and photolysis of acyloins: a new acylation of pyrroles and indole

Photolysis of the acyloins obtained by reaction of biacetyl with pyrroles and indole readily affords, in high yield, 2-acetylpyrroles and 3-acetylindole, respectively.

Photochemical synthesis of 3-heteroarylpyridines

Photolysis of 3-iodopyridine in the presence of five-membered aromatic heterocycles such as furan, thiophen, pyrrole, or 1-methylpyrrole provides a simple and potentially general preparation of 3-heteroaryl derivatives of pyridine.