Conventional approaches to Pd-catalyzed alkene 1,2-carboamination rely upon the combination of a nucleophilic nitrogen-based component and an internal C-based or external oxidant. In this study, we outline an umpolung approach, which is triggered by oxidative initiation at an electrophilic N-based component and employs "standard" organometallic nucleophiles to introduce the new carbon-based fragment. Specifically, oxidative addition of a Pd(0)-catalyst into the N-O bond of O-pentafluorobenzoyl oxime esters generates imino-Pd(II) intermediates, which undergo 5-exo cyclization with sterically diverse alkenes. The resultant alkyl-Pd(II) intermediates are intercepted by organometallic nucleophiles or alcohols, under carbonylative or noncarbonylative conditions, to provide 1,2-carboamination products. This approach provides, for the first time, a unified strategy for achieving alkene 1,2-amino-acylation, -carboxylation, -arylation, -vinylation, and -alkynylation. For carbonylative processes, orchestrated protodecarboxylation of the pentafluorobenzoate leaving group underpins reaction efficiency. This process is likely a key feature in related Narasaka-Heck cyclizations and accounts for the efficacy of O-pentafluorobenzoyl oxime esters in aza-Heck reactions of this type.
The
rotational speed of an overcrowded alkene-based molecular rotary
motor, having an integrated 4,5-diazafluorenyl coordination motif,
can be regulated allosterically via the binding of metal ions. DFT
calculations have been used to predict the relative speed of rotation
of three different (i.e., zinc, palladium, and platinum) metal dichloride
complexes. The photochemical and thermal isomerization behavior of
these complexes has been studied in detail using UV–vis and 1H NMR spectroscopy. Our results confirm that metal coordination
induces a contraction of the diazafluorenyl lower half, resulting
in a reduction of the steric hindrance in the “fjord”
region of the molecule, which causes an increase of the rotational
speed. Importantly, metal complexation can be accomplished in situ and is found to be reversible upon the addition
of a competing ligand. Consequently, the rotational behavior of these
molecular motors can be dynamically controlled with chemical additives.
Copper catalyzed Heck-like cyclizations of oxime esters are described. This new protocol is an effective alternative to Pd-based systems and highlights the value of replacing precious metal catalysts with cheaper and more sustainable variants.
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