Rick C. White

A Chemoenzymatic Total Synthesis of the Protoilludane Aryl Ester (+)-Armillarivin

The title natural product, 1, has been synthesized in 20 steps from the enantiomerically pure cis-1,2-dihydrocatechol 2, itself obtained through the whole-cell biotransformation of toluene. The pivotal steps in the reaction sequence involve a Diels-Alder cycloaddition reaction between diene 2 and cyclopentenone (3) and the photochemically promoted 1,3-acyl rearrangement of the bicyclo[2.2.2]oct-4-en-1-one 20 derived from the cycloadduct 4.

Photolysis of N-phenylhydroxylamine : a novel photochemical disproportionation reaction in N-O bond cleavage assisted by hydrogen bonding

The photochemistry of N-phenylhydroxylamine (9) has been examined in the solution phase and in the solid state. The major products are aniline and nitrosobenzene. The nitrosobenzene quickly reacts with 9 to generate azoxybenzene and with aniline to produce azobenzene. The quantum yields for the disappearance of 9 are reasonably high (0.25–0.29) and suggest that the photochemical reactions proceed from a hydrogen-bonded dimer.

The photochemistry of amides and amide derivatives. 3 : The photolysis of methyl-2-phenoxybenzohydroxamate

The photochemistry of methyl-2-phenoxybenzohydroxamate was studied. This compound was found to undergo the type I reaction followed by intramolecular cyclization to generate xanthone, the type II reaction to generate 2-phenoxybenzamide, and a formal 1,5 shift of the phenyl group from the benzohydroxamate ring to the nitrogen. It was also found that the relative amounts of the type II product and the phenyl migration product were solvent dependent. Photolysis in methanol favored the phenyl migration process whereas photolysis in cyclohexane favored the type II process. These results are attributed to an increased amount of single electron transfer from the phenoxy group to the carbonyl group relative to the type II process in methanol. The photolysis of N,N-dimethyl-2-phenoxybenzamide, which cannot undergo phenyl migration, gives xanthone as the only product.

Ring contraction in the photochemistry of 1,2-dihydronaphthalene oxide

Abstract The photochemistry of 1,2-dihydronaphthalene oxide was studied in order to determine the pathway by which rearrangement to ring-contracted products occurs. The amounts of indan were found to be the same in both acetonitrile and 1,4-dioxane which suggests that the process is diradical and not ionic. The substituted oxirane, 4,4-dimethyl-1,2-dihydronaphthalene oxide, was photolyzed in order to distinguish between a Grob-type fragmentation pathway and a simple 1,2-alkyl shift and it was found that indan ultimately originates from a 1,2- alkyl shift to form 1-formylindan followed by decarbonylation. It was also found that, although indan is not a primary photoproduct, it is formed very early in the reaction mixture, whereas the concentration of its precursor 1-formylindan remains low. Both sensitization and quenching experiments have shown that this is not a result of a bimolecular radical reaction, but rather due to the starting material sensitizing the initially formed aldehyde.

Geometric requirements for the photolysis of aryloxiranes and cyclic carbonate esters

Abstract The photolysis of trans -β-methylstyrene oxide proceeds smoothly, but neither the corresponding cis -isomer nor β,β-dimethylstyrene oxide are photochemically active. Moreover, although styrene glycol carbonate undergoes photolysis to extrude carbon dioxide, the β,β-dimethylstyrene glycol carbonate is photochemically unreactive. These results are explained by looking at the energies required to obtain a conformation in which the plane of the aromatic ring is orthogonal to the orbitals of the epoxide moiety.

Photolysis of alkyl N-alkylbenzohydroxamates

Abstract The photochemistry of alkyl N -alkylbenzohydroxamates)PhCONR 1 OR 2 ) was studied. These compounds give both type I (benzaldehyde) and type II ( N -alkylbenzamides) products. Although alkyl benzohydroxamates (PhCONHOR) undergo the type II process exclusively through the triplet state, the alkyl N -alkylbenzohydroxamates have both singlet and triplet contribution to the type II process. The type I process for the alkyl N -alkylbenzohydroxamates occurs via the singlet state and has not been observed previously in benzohydroxamate photochemistry. When changing from a more polar to a less polar solvent, the quantum yields of the type II product increase. This differs from the type II process of alkylbenzohydroxamates which shows no solvent effect and that of aryl alkanones which shows the opposite effect. The solvent effect observed here is attributed to intramolecular hydrogen bonding in the hydroxy 1,4-diradical.