171557-83-8Relevant articles and documents
Iodine(III)-Mediated Contraction of 3,4-Dihydropyranones: Access to Polysubstituted γ-Butyrolactones
Dagenais, Robin,Lussier, Tommy,Legault, Claude Y.
supporting information, p. 5290 - 5294 (2019/09/03)
Functionalized γ-butyrolactones are privileged structures in the field of medicinal chemistry; they are found in numerous natural products and synthetic compounds with diverse biological activities. The oxidative ring contraction of 3,4-dihydropyran-2-one derivatives represents a promising yet underappreciated strategy to access these compounds. To the best of our knowledge, very few examples of this strategy have been reported, with limited investigation of the influence of stereogenic centers on the starting dihydropyranones. We investigated the iodine(III)-mediated contraction of a representative set of dihydropyranone derivatives. The method gives rapid access to functionalized γ-butyrolactones in good yields. The reaction scope was investigated, and the method was found to support various levels of substituents, even enabling access to sterically congested quaternary centers. The stereoselectivity was investigated using chiral substrates and a chiral iodine(III) reagent.
Ring closure reactions of substituted 4-pentenyl-1-oxy radicals. The stereoselective synthesis of functionalized disubstituted tetrahydrofurans
Hartung,Gallou
, p. 6706 - 6716 (2007/10/03)
N-(Alkyloxy)pyridine-2(1H)-thiones 3 and benzenesulfenic acid O-esters 5 have been synthesized from substituted 4-pentenols 1 or the derived tosylates. Compounds 3 and 5 are efficient sources of free alkoxy radicals 6 which undergo synthetically useful fast ring closure reactions 6 → 8 [k(exo) = (2 ± 1) x 108 s-1 to (6 ± 2) x 109 s-1 (T = 30 ± 0.2°C)]. Tetrahydrofurfuryl radicals 8 can be trapped with, e.g., hydrogen or chlorine atom donors to afford either trans- or cis-disubstituted tetrahydrofurans 10 or 12 depending on the substitution pattern of the 4-pentenyloxy radical. Substituted tetrahydropyrans 11 or 13 are formed in the minor 6-endo-trig cyclization. According to the data of competition kinetics, the observed stereoselectivities in free alkoxy radical cyclizations arise from steric interactions between the substituents in the transition state of the ring closure reactions. Alkyl substituents cause small differences in the measured relative rate constants of 5-exo cyclizations which are reminiscent of the data obtained from the rearrangements of alkyl-substituted 5-hexenyl radicals. Likewise, a stereochemical model for oxygen radical cyclization is proposed where the pentenyloxy chain adopts a six-membered, chairlike transition state with the alkyl substituents preferentially situated in the pseudoequatorial positions leading to 2,5-trans-, 2,4-cis-, and 2,3-trans-substituted tetrahydrofurfuryl radicals 8 as the major intermediates.
