Herein, we describe the fast, chemoselective, and clean reduction of imines with zirconocene chloride hydride. The reaction works well on aromatic and enolizable aliphatic aldimines, as well as ketimines. A range of N-protecting groups and various functional groups were tolerated in the imine struc-
An
efficient diastereoselective synthesis of planar chiral ferrocenes
via Pd(II)-catalyzed direct C–H activation with arylboronic
acids or pinacol esters is presented. The reaction was performed under
mild conditions using commercially available achiral or chiral amino
acids as ligands. The best results were obtained with (R)-Boc-alanine, which yielded products in 27–83% yield with
diastereoselectivities ranging from 5:1 to 20:1 (11 examples). Diastereoisomeric
products can also be obtained using (S)-Boc-alanine
as a ligand. Stereoinduction of the reaction was explained by density
functional theory calculations of possible transition states.
Heterocycles possessing multiple substituents and stereogenic centers are important structural motifs in many compounds of interest. We present here stereoselective tandem transformation based on Cu‐catalyzed conjugate addition of Grignard reagents to heterocyclic Michael acceptors, which is followed by one‐pot trapping of in situ formed enolates with stabilized carbocations or their equivalents. The transformations are highly enantio‐ and diastereoselective with Josiphos‐type ferrocene ligand. The reaction of chiral metal enolates with onium compounds allows the installation of structurally attractive substituents on chromenone or piperidinone core. Moreover, cycloheptatrienyl and benzodithiolyl substituents can be further modified, thus expanding synthetic possibilities of this methodology.
We present here a stereoselective tandem reaction based on the asymmetric conjugate addition of dialkylzinc reagents to unsaturated acylimidazoles followed by trapping of the intermediate zinc enolate with carbocations. The use of a chiral NHC ligand provides chiral zinc enolates in high enantiomeric purities. These enolates are reacted with highly electrophilic onium compounds to afford densely substituted acylimidazoles. DFT calculations helped to understand the reactivity of the zinc enolates derived from acylimidazoles and allowed their comparison with metal enolates obtained by other conjugate addition reactions.
An improved, short and efficient synthesis of vinylferrocene is reported. This three-step synthesis includes Friedel–Crafts acylation, reduction, and a one-pot mesylation/elimination step to afford the target compound in 62% yield over three steps.
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