A series of azomethine-based HTMs is synthesized using simple condensation chemistry. Their photovoltaic performance and moisture barrier properties are presented.
We
report herein versatile, transition metal-free and additive-free
(hetero)aryl–aryl coupling reactions promoted by the oxidative
electrocoupling of unsymmetrical tetra(hetero)arylborates (TABs) prepared
from ligand-exchange reactions on potassium trifluoroarylborates.
Exploiting the power of electrochemical oxidations, this method complements
the existing organoboron toolbox. We demonstrate the broad scope,
scalability, and robustness of this unconventional catalyst-free transformation,
leading to functionalized biaryls and ultimately furnishing drug-like
small molecules, as well as late stage derivatization of natural compounds.
In addition, the observed selectivity of the oxidative coupling reaction
is related to the electronic structure of the TABs through quantum-chemical
calculations and experimental investigations.
Spurred on by the recent emerging interest from the chemical community for unsaturated four-membered heterocycles, an unprecedented approach to nitrogen-containing four-membered rings has been designed. 3,4-Disubstituted 2-azetines were synthesized from commercially available substrates, allowing for a straightforward access to a new library of chiral functionalized azetidines and amino alcohols. This original approach was applied to efficiently prepare functionalized azobenzenes, an emerging class of molecules with a large potential in photopharmacology.
Conventional methods carrying out C(sp
2
)−C(sp
2
) bond formations are typically mediated by transition‐metal‐based catalysts. Herein, we conceptualize a complementary avenue to access such bonds by exploiting the potential of electrochemistry in combination with organoboron chemistry. We demonstrate a transition metal catalyst‐free electrocoupling between (hetero)aryls and alkenes through readily available alkenyl‐tri(hetero)aryl borate salts (ATBs) in a stereoconvergent fashion. This unprecedented transformation was investigated theoretically and experimentally and led to a library of functionalized alkenes. The concept was then carried further and applied to the synthesis of the natural product pinosylvin and the derivatization of the steroidal dehydroepiandrosterone (DHEA) scaffold.
Described is the in situ formation of triorganocerium reagents and their application in catalyst‐free Zweifel olefinations. These unique cerium species were generated through novel exchange reactions of organohalides with n‐Bu3Ce reagents. The adequate electronegativity of cerium allowed for compensating the disadvantages of both usually functional‐group‐sensitive organolithium species and less reactive organomagnesium reagents. Exchange reactions were performed on aryl and alkenyl bromides, enabling enantiospecific transformations of chiral boron pinacol esters. Finally, these new organocerium species were engaged in selective 1,2‐additions onto enolisable and sterically hindered ketones.
Following recent advances in the generalization and simplification of 2H-azetine synthesis, a regiodivergent approach to fused 2- and 3-alkylideneazetines was designed via the intermediate formation of unprecedented vinylazetine structures. Concise sequences to the latter are described from which an expected unsaturated fused ring system was isolated with very high yields and regio- and stereoselectivities by [4 + 2] cycloadditions.
Readily accessible tetraorganoborate salts undergo selective coupling reactions under blue light irradiation in the presence of catalytic amounts of transition‐metal‐free acridinium photocatalysts to furnish unsymmetrical biaryls, heterobiaryls and arylated olefins. This represents an interesting conceptual approach to forge C−C bonds between aryl, heteroaryl and alkenyl groups under smooth photochemical conditions. Computational studies were conducted to investigate the mechanism of the transformation.
A simple and efficient diastereoselective synthesis of methylenecyclopropanes is described, in which boron-homologation and allylboration are merged into a one-pot process, starting from in situ generated cyclopropenyllithium species. This unprecedented methodology opens a new route to strained alkylidenecycloalkanes containing a quaternary stereocenter, in high yields and excellent diastereomeric ratios.
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