The palladium-catalyzed solid-state CÀ N cross-coupling of carbazoles with aryl halides via a high-temperature ball-milling technique has been reported. This reaction allowed simple, fast, and efficient synthesis of N-arylcarbazole derivatives in good to excellent yields without the use of large amounts of organic solvents in air. Importantly, the developed solid-state coupling approach enabled the cross-coupling of poorly soluble aryl halides with large polyaromatic structures that are barely reactive under conventional solution-based conditions.
A new
series of C
1-symmetric P-chirogenic
bisphosphine ligands of the type (R)-5,8-Si-Quinox-tBu3 (Silyl = SiMe3, SiEt3, SiMe2Ph) have been developed.
The bulky silyl modulators attached to the ligand backbone fix the
phosphine substituents to form rigid chiral environments that can
be used for substrate recognition. The ligand showed high performances
for a copper(I)-catalyzed asymmetric borylative cyclopropanation of
bulky silyl-substituted allylic electrophiles to afford higher disfavored
1,2-cis-silyl-boryl-cyclopropanes than the other
possible isomers, trans-cyclopropane and allylboronate
(up to 97% yield; 98% ee; cis/trans = >99:1; cyclopropane/allylboronate = >99:1). Detailed computational
studies suggested that the highly rigid phosphine conformation, which
is virtually undisturbed by the steric interactions with the bulky
silyl-substituted allyl electrophiles, is key to the high stereo-
and product-selectivities. Furthermore, the detailed computational
analysis provided insight into the mechanism of the stereoretention
or -inversion of the chiral alkylcopper(I) intermediate in the intramolecular
cyclization.
A copper(I)-catalyzed
linear-selective allylation of carbonyl compounds
with trisubstituted allylboronates has been achieved by capitalizing
on the electronic and steric effects of silyl groups. This reaction
provides stereodefined trisubstituted homoallyl alcohol derivatives
that bear a synthetically useful alkenyl silane moiety. The results
of a computational study suggested that the silyl directing group
thermodynamically stabilizes
the sterically hindered allylcopper(I) intermediate and kinetically
facilitates the carbonyl allylation path for the linear product by
lowering the energy of its transition state.
The electrochemical reduction conditions of the reaction of alkyl 2-chloroacetates in Bu4NBr/DMF using a divided cell equipped with Pt electrodes to produce the corresponding cyclopropane derivatives in moderate yields were discovered. The reaction conditions were optimized, the scope and limitations, as well as scale-up reactions were investigated. The presented method for the electrochemical production of cyclopropane derivatives is an environmentally friendly and easy to perform synthetic procedure.
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