83126-03-8Relevant academic research and scientific papers
Controlling 6-endo-selectivity in oxidation/bromocyclization cascades for synthesis of aplysiapyranoids and other 2,2,6,6-substituted tetrahydropyrans
Brücher, Oliver,Bergstr??er, Uwe,Kelm, Harald,Hartung, Jens,Greb, Marco,Svoboda, Ingrid,Fuess, Hartmut
supporting information; experimental part, p. 6968 - 6980 (2012/09/07)
A cascade, composed of (i) oxovanadium(V)-catalyzed oxidation of bromide by tert-butyl hydroperoxide and (ii) stereoselective 6-endo-bromocyclization, affords 3-bromo-2-aryl-2,6,6-trimethyltetrahydropyrans from styrene-type tertiary alkenols in synthetically useful yields. (E)-Alkenols add the bromo- and the alkoxy substituent anti-selectively across the double bond, indicating a bromonium ion-mechanism for the ring closure. 6-endo-control of the alkenol cyclization thereby arises from the polar effect of the aryl substituent. Two methyl substituents bound to the alkene terminus are not similarly able to favor 6-endo-cyclization, because strain arising from methyl group repulsion, as the bromonium-activated π-bond and the hydroxyl oxygen approach, directs bromocyclization of tertiary prenyl-type substrates toward tetrahydrofuran formation. A hexasubstituted bromotetrahydropyran prepared from the oxidation/bromocyclization cascade served as starting material for synthesis of racemic aplysiapyranoid A, in a sequence of free radical and polar functional group interconversion.
Reactivity of 1-Cyclopropene-1-carboxylic Acid Lactones Dependent on the Size of the Lactone Ring
Frenking, Gernot,Huelskaemper, Ludwig,Weyerstahl, Peter
, p. 2826 - 2835 (2007/10/02)
The reaction of the bicyclic γ-lactone 1 with KOtBu leads to lactone 3 by addition of tert-butoxide at the 1-position of the intermediate cyclopropene lactone 2 and subsequent exo-protonation.In contrast, the δ-lactone 13, readily available from cinnamyl
