Study On Photochemical Synthesis Of Benzofurans By NORRISH Type Ⅱ Reaction

Benzofuran neolignans are widely found in natural products and they have been shown to have bioactivities. However, the compounds isolated from plants are in small amount that can't meet people's needs, thus it is very important to find a way to synthesize it. Traditional synthetic methods for benzofurans are tedious, waste of reagents and can't tolerate a variety of functional groups.Ketones with certain structure can generate a 1,4-diradical byγ-hydrogen abstraction of a photoexcited carbonyl group and then form a four-membered ring alcohol, this is named as Norrish typeⅡreaction. This mechanism of Norrish typeⅡreaction enlighten us that aromatic ketones with certain structure may produce benzofurans under UV irradiations, this could be a novel way to synthesize benzofurans. In this essay, we focus on synthesis of Ocophyllals A using Norrish typeⅡreaction as the key step. Ocophyllals A is a new benzofuran neolignan isolated from Ocotea macrophylla Kunth.The first part of this thesis, we designed two precursors which could be photochemically converted into Ocophyllas A. We attempted to synthesize the two precursors via four different routes respectively, finally we successfully synthesized one precursor methyl 3-acetyl-4-(benzyloxy)-5-methoxybenzoate starting from o-vanillin in eight steps.The second part we investigated the Norrish typeⅡphotochemical reaction of methyl 3-acetyl-4-(benzyloxy)-5-methoxybenzoate: in the solid-state the photochemical reaction didn't occur at all. We thought that the reactant might need much higher energy; While the reaction was conducted in the solvents, such as acetonitrile, benzene and acetone, methyl 3-acetyl-4-(benzyloxy)-5-methoxybenzoate generated new products, but unfortunately, the products were not isolated successfully, this is because the products were not stable on the silica gel column.