21016-47-7Relevant academic research and scientific papers
Asymmetric dihydroxylation of β,γ-unsaturated carboxylic esters with trisubstituted C=C bonds - Enantioselective syntheses of trisubstituted γ-butyrolactones
Kapferer, Tobias,Brueckner, Reinhard
, p. 2119 - 2133 (2007/10/03)
β,γ-Unsaturated esters with stereodefined trisubstitued C=C double bonds were prepared by the Arndt-Eistert homologation of α,β-unsaturated carboxyl halides, by two-step methoxycarbonylation of allylbarium reagents, by deconjugation of α,β-unsaturated esters, and by Horner-Wadsworth-Emmons variants of the Stobbe condensation. Sharpless asymmetric dihydroxylation of the β,γ-unsaturated esters, followed by spontaneous cyclization, afforded β-hydroxy-γ-lactones in moderate to good yields and with enantiomeric excesses of up to 97 %. Similarly, tetrahydroxy-γ-lactones were obtained from diunsaturated esters; these lactones were converted into a bislactone and an unsaturated β-hydroxy γ-lactone. Wiley-VCH Verlag GmbH & Co. KGaA, 2006.
A general and diastereoselective approach to the preparation of cis-2,6-disubstituted pyrans
Varelis, Peter,Johnson, Brian L.
, p. 43 - 51 (2007/10/03)
The utility of preparing cis-2,6-disubstituted 5,6-dihydro-2H-pyrans by the methodology implied in Scheme 1 is demonstrated through the preparation of the two pyrans (1) and (2). The overall yields for the two nine-step sequences starting from the enals (3) and (4) were 57 and 54%, respectively, whilst the overall diastereochemical yield approached 100%. The key features of the method are (i) a highly regioselective Lewis acid-catalysed cyclocondensation reaction of a nucleophilic diene with an aldehyde to afford a 2,3-dihydro-4H-pyran-4-one, (ii) reduction of a pyranone with better than 98% regio- and stereo-chemical control to give the corresponding glycal, and (iii) an ester enolate Claisen rearrangement of a glycal acetate.
1,3-Dimethyl 2-oxo 1,3,2-diazaphospholidine precursor of (Z) α,β-unsaturated esters
Patois,Savignac
, p. 1317 - 1320 (2007/10/02)
α,β-Unsaturated esters of (Z) geometry are selectively obtained from cyclic phosphonocarboxylates derived from N,N'-dimethylethylenediamine.
PHOTODECONJUGAISON ENANTIOSELECTIVE D'ESTERS ET DE LACTONES CONJUGUEES EN PRESENCE D'EPHEDRINE
Henin, Francoise,Mortezaei, Reza,Muzart, Jacques,Pete, Jean-Pierre,Piva, Oliverier
, p. 6171 - 6196 (2007/10/02)
α,β-unsaturated esters and α-alkylidene lactones bearing one γ-hydrogen on the unsaturated chain, were deconjugated by irradiation with UV light (λ=254 nm).When the reaction was carried out in the presence of (+) or (-) ephedrine, an enantioselective C-protonation of the photodienolic intermediate led to the deconjugated ester with an enantiomeric excess up to 30 percent.The scape of the reaction and the configuration of the new asymmetric center are discussed.
