小員環ラクトン類を用いる天然物の炭素骨格形成

概要

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Regioselective ring cleavage of small membered lactones provides the convenient synthesis of various types of carbon homologated carboxylic acids : e. g. highly strained four-membered lactones, such as β-propiolactones or diketene give three carbon homologated β-substituted propionic is acids or 3-methylenealkanoic acids, respectively, by the regioselective attack of organometallics to their β-carbons. On the other hand, lactones with an unsaturated group at their w position, such as β-vinyl- and β-ethynyl-β-propiolactones, γ-vinyl-γ-butyrolactone or δ-vinyl-δ-valerolactone give five, six, or seven carbon homologated carboxylic acids with olefinic bond (s), respectively, by S<SUB>N</SUB>2 reaction of the organocopper reagents with their terminal unsaturated carbons. These lactones are extremely useful as synthetic blocks for natural product syntheses due to the selective construction of carbon skeleton and an easy conversion of the carboxylic functional group to other functional ones. The synthetic utility of the lactones is demonstrated by the following natural products : perfumes and essential oils, insect pheromones and hormones, insecticides, and macrolides.
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