Herein, we describe
the generation of an organochromium-type carbanion
species from a non-activated C–H bond and its nucleophilic
addition to aldehydes. The catalytic carbanion generation occurred
through formal deprotonation of a non-activated C–H bond under
mild conditions and did not need the prefunctionalization or anion
stabilizing group. Carbon radical intermediates generated by decatungstate
photocatalyst-mediated hydrogen abstraction were captured by a chromium
salt with the reductive radical-polar crossover reaction to produce
organochromium carbanions.
Currently, catalytically transferable carbenes are limited to electron-deficient and neutral derivatives, and electron-rich carbenes bearing an alkoxy group (i.e., Fischer-type carbenes) cannot be used in catalytic cyclopropanation because of the lack of appropriate carbene precursors. We report herein that acylsilanes can serve as a source of electron-rich carbenes under palladium catalysis, enabling cyclopropanation of a range of alkenes. This reactivity profile is in sharp contrast to that of metal-free siloxycarbenes, which are unreactive toward normal alkenes. The resulting siloxycyclopropanes serve as valuable homoenolate equivalents, allowing rapid access to elaborate β-functionalized ketones.
Nickel-catalyzed decarbonylation
of acylsilanes is developed. In
sharp contrast to cross-coupling reactions of acylsilanes, in which
the silyl group serves as a leaving group, the silyl group is retained
in the product in this decarbonylation reaction. Although the strong
binding of the dissociated CO to the nickel center frequently hinders
catalyst turnover in nickel-mediated decarbonylative reactions, this
reaction can be catalyzed by nickel complexes bearing a CO ligand.
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