Chiral orthoesters in organic synthesis: Novel reagents for the enantioselective acylation of silylenolethers
摘要:
Dialkyl trans-2-alkoxy-2-alkyl-1,3-dioxolan-4,5-dicarboxylates and the corresponding N,N,N,N-tetramethyl-4,5-diamides have been prepared respectively from dialkyl tartrates or tartaric acid diamides. They smoothly reacted with silylenolethers in the presence of Lewis acids to give enantiomerically enriched (up to 90% d.e.) monoprotected 1,3-diketones. A dramatic dependence of the stereochemical outcome from the configuration of the enolic double bond of 4 has been observed. The products can be stereoselectively reduced to give configurationally defined monoprotected 3-ketols.
Nickel(0) species generated in situ from NiBr2(PPh3)2–Zn–PPh3catalyzed the formation of unsaturated nitriles from vinylhalides and potassium cyanide. The reaction proceeded under very mild conditions and was stereoselective.
high stereoselectivity at 50 °C by almost all of the procedures attempted. On the contrary, the KCN–HMPA and KCN–MeCN systems with low cyanide solubilities accelerated the coupling of the halides to inhibit the cyanation, and in general the NaCN–DMF and NaCN–HMPA systems with high cyanide solubilities needed to reduce Ni(II) before adding MCN in order to make the catalytic reaction start. Vinyl halides
The Pd-catalyzed cross coupling of either benzylzincs with alkenyl halides or alkenylalanes with benzyl halides provides highly selective and expeditious routes to allylated arenes.
[EN] BENZO- SEVEN-MEMBERED HETEROCYCLIC COMPOUND, PREPARATION METHOD THEREFOR, PHARMACEUTICAL COMPOSITION THEREOF, AND APPLICATION THEREOF<br/>[FR] COMPOSÉ HÉTÉROCYCLIQUE À SEPT CHAÎNONS BENZO, SON PROCÉDÉ DE PRÉPARATION, COMPOSITION PHARMACEUTIQUE DE CELUI-CI ET SON APPLICATION<br/>[ZH] 苯并七元杂环类化合物、其制备方法、药物组合物及应用