Osamu Soga

Structural influences on the isomerization of 4-benzyl- and 4-allyl-1,2-naphthoquinones to quinonemethides and their stereochemistry

The isomerization of 4-benzyl-1,2-naphthoquinones and 4-allyl-1,2-naphthoquinones to quinonemethides has been studied. The steric interaction and extra π conjugation in the quinonemethide, and acidity of methylene protons of the quinone, are controlling factors for the isomerization. 1H N.m.r. studies suggested that the quinonemethides have the E configuration.

The photochemical reaction of 1,2-naphthoquinone with hydrogen donors. An explanation of the coupling sites of alkyl and acyl radicals to 1,2-naphthosemiquinone radical

The photoinduced addition reactions of toluene, diphenylmethane, phenylacetaldehyde, and diphenylacetaldehyde to 1,2-naphthoquinones have been investigated. Benzyl and diphenylmethyl radicals attack the 4-position of 1,2-naphthosemiquinone radical, whereas phenylacetyl radical attacks both the 3-position and the oxygen atoms of the semiquinone radical. The different attacking patterns of alkyl and acyl radicals to the semiquinone radical are successfully interpreted by taking into consideration the charge densities of the radicals concerned.

Mechanism of light-induced reductive acetylation of 1,2-naphthoquinone with acetaldehyde

The detailed mechanism of the photochemical reaction of 1,2-naphthoquinone with acetaldehyde has been investigated. From a study of the reaction using the 1H CIDNP technique and change of the product distribution with temperature, it was deduced that the almost all parts of the reaction proceed via an ‘in-cage’ mechanism at a low temperature, but at 20 °C at least 6.7% of the reaction proceeds via an ‘out-of-cage’ mechanism. For comparison, the addition of thermally generated acetyl radical to 1,2-naphthoquinone has also been examined.

Isolation of a New Natural Quinone, 2-Hydroxy-6-methoxy-3,5-dimethyl- 1,4-benzoquinone, from the Potato Culture Solation of Phoma wasabiae Yokogi

2-Hydroxy-6-methoxy-3,5-dimethyl -1,4- benzoquinone was found in the blackish potato culture solution of Phoma wasabiae.

Photochemical reduction of 1,2-naphthoquinones with xanthen. Investigation by means of a photo-CIDNP technique

Photochemical reactions of 1,2-naphthoquinone and its derivatives with xanthen, a hydrogen donor, have been investigated. 1,2-Naphthoquinones, in general, produced the stable adducts (2), 9,9′-bixanthenyl, and xanthone together with a small amount of quinhydrones. 4-Substituted 1,2-naphthoquinones, however, gave the corresponding naphthalene-1,2-diols as the major products. Investigation by means of a CIDNP technique indicated the formation of unstable products, judging from the strongly polarized 1H n.m.r. signals, though the unstable intermediates did not accumulate in the reacting solution. Adducts (2), naphthalene-1,2-diols, and 1,2-naphthoquinones themselves also showed polarized 1H n.m.r. signals. From these results, the reaction mechanism was deduced.