光環状付加反応を用いるテルペノイドの合成

抄録

Photocycloaddition reactions as synthetic methods for carbon frameworks of terpenoids were reviewed with particular emphasis of the enolized β - diketone photocycloaddition, de Mayo reaction, of methyl 2, 4- dioxoalkanoates developed in the authors' laboratory. In contrast to simple β- diketone, e.g., acetylacetone, methyl-2, 4-dioxoalkanoates, thoroughly existing in linearly conjugated structure in various media, cycloadd regiospecifically to various olefinic compounds upon UV irradiation. Thus, conjugated olefins having other functional groups in a vicinity smoothly produced [2 + 2] π cycloadducts from which further transformations could be conveniently carried out. In addition to the well- documented cyclization to cyclohexenones, the cyclopentene formation via reductive cyclization extended the usefulness of the method. Using this procedure, we have synthesized several terpenoids, from a monoterpenoid, dehydroiridodial, to a diterpene, cycloaraneosene, some of which have been discussed in detail. Although a few side reactions are found in this photocycloaddition, generality of this new version of de Mayo reaction is satisfactory.