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.
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 / D'Annibale, Andrea; Ciaralli, L; Bassetti, M.; Pasquini, C.. - In: JOURNAL OF ORGANIC CHEMISTRY. - ISSN 0022-3263. - STAMPA. - 72(2007), pp. 6067-6074.
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Titolo: | 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 |
Autori: | |
Data di pubblicazione: | 2007 |
Rivista: | |
Citazione: | 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 / D'Annibale, Andrea; Ciaralli, L; Bassetti, M.; Pasquini, C.. - In: JOURNAL OF ORGANIC CHEMISTRY. - ISSN 0022-3263. - STAMPA. - 72(2007), pp. 6067-6074. |
Handle: | http://hdl.handle.net/11573/44172 |
Appartiene alla tipologia: | 01a Articolo in rivista |