Enantioselective, Desymmetrizing Bromolactonization of Alkynes
摘要:
Asymmetric bromolactonizations of alkynes are possible using a desymmetrization approach. The commercially available catalyst (DHQD)(2)PHAL promotes these cyclizations in combination with cheap NBS as a bromine source to give bromoenol lactones in high yield and with high enantioselectivity. The bromoenol lactone products, containing a tetrasubstituted alkene and a quaternary stereocenter are valuable building blocks for synthetic chemistry.
Pd(ii)–SDP-catalyzed enantioselective 5-exo-dig cyclization of γ-alkynoic acids: application to the synthesis of functionalized dihydofuran-2(3H)-ones containing a chiral quaternary carbon center
The gold-catalyzed desymmetrization of alkynylmalonicacids proceed smoothly to give chiral lactones with high yield and ee. Control experiments and DFT calculations indicate that the amino group of the ligands and the alcohol additives play key roles in the control of enantioselectivity.
Cycloisomerization versus Hydration Reactions in Aqueous Media: A Au(III)-NHC Catalyst That Makes the Difference
作者:Eder Tomás-Mendivil、Patrick Y. Toullec、Josefina Díez、Salvador Conejero、Véronique Michelet、Victorio Cadierno
DOI:10.1021/ol300811e
日期:2012.5.18
A novel water-soluble Au(III)-NHC complex has been synthesized and successfully applied in the intramolecular cyclization of gamma-alkynoic acids into enol-lactones under biphasic toluene/water conditions, thus representing a rare example of an active and selective catalyst for this transformation In aqueous media. Remarkably, competing alkyne hydration processes were not observed, even during the desymmetrization reaction of challenging 1,6-diyne substrates. In addition, after phase separation, the water-soluble Au(III) catalyst could be recycled 10 times without loss of activity or selectivity.