Synthesis of Alkyl-Substituted Six-Membered Lactones through Ring-Closing Metathesis of Homoallyl Acrylates. An Easy Route to Pyran-2-ones, Constituents of Tobacco Flavor

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• 作者：Andrea D'Annibale ; Laura Ciaralli ; Mauro Bassetti ; Chiara Pasquini
• 刊名：Journal of Organic Chemistry
• 出版年：2007
• 出版时间：August 3, 2007
• 年：2007
• 卷：72
• 期：16
• 页码：6067 - 6074
• 全文大小：143K
• 年卷期：v.72,no.16(August 3, 2007)
• ISSN：1520-6904

文摘

The ring-closing metathesis (RCM) reactions of homoallylic acrylates bearing alkyl substituents on variouspositions of their skeleton afford the corresponding pentenolides in the presence of carbene rutheniumcatalysts. For R³ = R⁴ = H, or R³ = Me, R⁴ = H, the reactions are catalyzed by complex [RuCl₂(PCy₃)₂(=CHPh)], while a second-generation Grubbs catalyst is required when R³ = H and R⁴ = Me, R³ = R⁴= Me, or R³ = i-Pr and R⁴ = H. Alkyl substitution at the homoallylic carbon (R¹, R²) increases the yieldof the reaction when both the acrylic and/or homoallylic double bonds are methyl-substituted. Theinteraction of the catalyst with the substrate in the initiation stage involves the homoallylic double bondrather than the acrylic moiety, and the resulting alkylidene species from the first-generation Grubbs catalystcan be observed by ¹H and ³¹P NMR. The racemic tobacco constituents 4-isopropyl-5,6-dihydropyran-2-one and 4-isopropyltetrahydropyran-2-one are prepared via a short reaction sequence, involving theRCM reaction as the key transformation.