A Ni(0)-BINAP system is utilized for the highly enantioselective alpha-arylation of alpha-substituted gamma-butyrolactones with aryl chlorides and bromides. alpha-Quaternization is achieved in moderate to excellent yields. Furthermore, the rate accelerating effect caused by the addition of Zn(II) salts is investigated.
An operationally simple and scalable synthesis of enantiomerically pure bicyclo[2.2.2]octadiene (bod*) ligands relying on an organocatalytic one-pot Michael addition-aldol reaction with cheap 2-cyclohexenone and phenylacetaldehyde is presented. The crystalline bicyclic product 4a (6-hydroxy-5-phenylbicyclo[2.2.2]octan-2-one) is transformed into phenylbicyclo[2.2.2]oct-5-en-2-one 2, a versatile starting material for the 2-step synthesis of both symmetrical, such as Hayashi's Ph-bod* ligand, as well as novel unsymmetrical chiral dienes.
The efficient preparation of [(S)-BINAP]Ni(COD) (1) and [(S)-BINAP]NiBr2 (2) is reported. X-ray
crystal structure analysis of these potential precatalysts
provides the first structural insights into the nickel−BINAP system at both the 0 and +2 oxidation states.
The total synthesis of protoporphyrin IX and its disodium salt using a new alternative method to the classical MacDonald condensation is reported. The key step is the reaction of the new unsymmetrical diiodo dipyrrylmethane 1 with the known dipyrrylmethane 2. Coupling of the two fragments leads directly to porphyrin 3 without the need of an oxidizing agent. The new methodology is well suited for the synthesis of protoporphyrin IX derivatives on a multi 100 g scale in good quality without the need for chromatography. Furthermore, these preparations are completely free of any contaminant of animal origin, which represents a real improvement in the manufacturing of protoporphyrin IX derivatives.
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