Triply convergent, stereospecific alkene formation via Peterson olefination
摘要:
alpha-Iodo silanes 8 were prepared from alpha-hydroxy silanes and after halogen/metal exchange and treatment with copper(I) bromide-dimethyl sulfide were coupled with acid chlorides to yield alpha-silyl ketones 2. Cram controlled addition with a variety of nucleophiles followed by treatment with acid or base led to either the (E)- or (Z)-alkene in good overall yields from the iodide (47-67%) and with excellent stereoselectivities ( > 95/ < 5 for disubstituted cases and 67/33 to 95/5 for trisubstituted). The procedure was used iteratively in the total synthesis of 4(E),8(Z)-tetradecadien-1-yl acetate (15) in > 95/ < 5 isomeric purity.
Ligand‐Enabled Nickel‐Catalyzed Redox‐Relay Migratory Hydroarylation of Alkenes with Arylborons
作者:Yuli He、Chuang Liu、Lei Yu、Shaolin Zhu
DOI:10.1002/anie.202001742
日期:2020.6.2
A redox-relay migratory hydroarylation of isomeric mixtures of olefins with arylboronic acids catalyzed by nickel complexes bearing diamine ligands is described. A range of structurally diverse 1,1-diarylalkanes, including those containing a 1,1-diarylated quaternary carbon, were obtained in excellent yields and with high regioselectivity. Preliminary experimental evidence supports the proposed non-dissociated
ligand-controlled nickel migration/arylation. This general protocol allows the use of abundant and bench-stable alkyl bromides and aryl bromides for the synthesis of a wide range of structurally diverse 1,1-diarylalkanes in excellent yields and high regioselectivities under mild conditions. We also demonstrated that alkyl bromide could be replaced by the proposed olefin intermediate while using n-propyl bromide/Mn0
A regiodivergent nickel‐catalyzed hydrocyanation of a broad range of internal alkenes involving a chain‐walking process is reported. When appropriate diastereomeric biaryl diphosphite ligands are applied, the same starting materials can be converted to either linear or branched nitriles with good yields and high regioselectivities. DFT calculations suggested that the catalyst architecture determines
is challenging, especially in asymmetric transformations. With each step in the catalytic cycle promoted by its privileged ligand and different steps well-connected by dynamic ligand exchange, synergistic combination of multiple ligands could potentially enhance the catalytic efficiency and selectivity. Now, this concept has been applied to the NiH-catalyzed asymmetric remote hydroacylation of olefins