Synthesis of 3-Methyl-2- (2-propeny1) -2-cyclopentenone from Methyl 3-Formylpropionate

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  • 3-ホルミルプロピオン酸メチルを用いる3-メチル-2- (2-プロペニル) -2-シクロペンテノンの合成
  • 3 ホルミルプロピオンサン メチル オ モチイル 3 メチル 2 2 プロペニ

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3-Methyl-2- (2-propeny1) -2-cyclopentenone (Allylrethrone, 1) is an important component of an insecticidal pyrethroid and an intermediate for the synthesis of pyrethrins.<BR>The procedure for the synthesis of (1) from methyl 3-formyl propionate (2) is shown in Scheme-1.<BR>Keto ester (4), prepared from (2) and 2-methyl-2-vinyl-1, 3-dioxolane (3) by radical addition reaction in 76 % yield, was treated with ethylene glycol to give diacetal (5) in 72 % yield. Reduction of (5) with sodium bis (2-methoxyethoxy) aluminium hydride in benzene gave diacetal alcohol (6) in 95 % yield, which was oxidized to diacetal aldehyde (7) with pyridinium chlorochromate in 66 % yield.<BR>Diacetal aldehyde (7) was reacted with the ylid prepared form methyltriphenylphosphonium iodide to give (8) in 91 % yield, which was hydrolyzed with hydrochloric acid to afford diketone (9) in 95 % yield. The base-catalized cyclization of (9) gave (1) in 92 % yield.

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