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Synthesis of Alkyl-Substituted Six-Membered Lactones Through Ring-Closing Metathesis of Homoallyl Acrylates. An Easy Route to Pyrans-2-ones, Constituents of Tobacco Flavor (Articolo in rivista)

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Synthesis of Alkyl-Substituted Six-Membered Lactones Through Ring-Closing Metathesis of Homoallyl Acrylates. An Easy Route to Pyrans-2-ones, Constituents of Tobacco Flavor (Articolo in rivista) (literal)

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D'Annibale Andrea; Ciaralli Laura; Bassetti Mauro; Pasquini Chiara (2007)
Synthesis of Alkyl-Substituted Six-Membered Lactones Through Ring-Closing Metathesis of Homoallyl Acrylates. An Easy Route to Pyrans-2-ones, Constituents of Tobacco Flavor
in Journal of organic chemistry; ACS, American chemical society, Washington, DC (Stati Uniti d'America)
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Istituto di Metodologie Chimiche, CNR, Roma; Dipartimento di Chimica, Università La Sapienza, Roma (literal)

Titolo

Synthesis of Alkyl-Substituted Six-Membered Lactones Through Ring-Closing Metathesis of Homoallyl Acrylates. An Easy Route to Pyrans-2-ones, Constituents of Tobacco Flavor (literal)

Abstract

The ring-closing metathesis (RCM) reactions of homoallylic acrylates bearing alkyl substituents on various positions of their skeleton afford the corresponding pentenolides in the presence of carbene ruthenium catalysts. For R-3 = R-4 = H, or R-3 = Me, R-4 = H, the reactions are catalyzed by complex [RuCl2(PCy3)(2)(CHPh)], while a second-generation Grubbs catalyst is required when R-3 = H and R-4 = Me, R-3 = R-4 = Me, or R-3 = i-Pr and R-4 = H. Alkyl substitution at the homoallylic carbon (R-1, R-2) increases the yield of the reaction when both the acrylic and/or homoallylic double bonds are methyl-substituted. The interaction of the catalyst with the substrate in the initiation stage involves the homoallylic double bond rather than the acrylic moiety, and the resulting alkylidene species from the first-generation Grubbs catalyst can be observed by H-1 and P-31 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 the RCM reaction as the key transformation. (literal)

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