86014-46-2Relevant academic research and scientific papers
Ring Cleavage of Benzofurans and Tetrahydrobenzofurans by m-Chloroperbenzoic Acid Epoxidation
Adam, Waldemar,Ahrweiler, Michael,Sauter, Markus
, p. 941 - 946 (2007/10/02)
The oxidation of the benzofurans 1a-f (tetrahydrobenzofurans 1g, h) with excess m-CPBA is reported.The in situ generated, highly reactive benzofuran epoxides 2a-f and their quinone methides 3a-f (cis-ene diones 3g, h) afford the labile tautomeric peroxy esters 5 and 5' by nucleophilic addition of the peroxy acid.On elimination of m-chlorobenzoic acid, the peroxy esters 5/5' of the benzofuran derivatives 1a-f rearrange thermally to the keto esters 6 by C-C cleavage or to the spiro epoxides 7 by C-O cleavage.The latter undergo thermal isomerization to the 1,3-benzodioxoles 8 and Diels-Alder cycloaddition to the corresponding dimers 9.Independently, the keto esters 6 and the 1,3-dioxoles 8 were synthesized by thermolysis of the dioxetanes 11.The tautomeric m-CPBA adducts 5/5' of the persistent ene diones 3g, h, derived from the tetrahydrobenzofuran derivatives 1g, h, rearrange as well to the spiro epoxides 7g, h.In contrast to the benzofuran derivatives 6a-f, the keto enol ester 6h suffers Baeyer-Villiger rearrangement with another molecule of m-CPBA to form the ene diester 10h. - Key Words: Epoxidation / Benzofuran / Benzofuran epoxide / Quinone methide / Benzofuran-2-one / 2,4-Cyclohexadien-1-one, spiroepoxide / cis-Ene dione / Perester, β-hydroxy- / 1,3-Benzodioxole / Keto enol ester
