The intermolecular deacylative coupling of unstrained
ynones via
C–C bond activation was accomplished by a CuCl–bpy system
under mild reaction conditions. This protocol features facile cleavage
of the C–C bond at room temperature, broad substrate scope,
and efficient construction of important symmetric and unsymmetrical
1,3-diyne adducts through homo or cross coupling of ynones, respectively.
The preliminary mechanistic investigations indicated that an acyl
copper(III) complex is likely involved in this process.
The [3+2] annulation of trifluoromethylated ketimines with acrylates has been enabled by rhenium-catalyzed C−H activation, delivering a variety of β-CF 3 β-amino esters. The reaction has exhibited broad substrate generality regarding aromatic CF 3 -ketimines and acrylates, the ability for gram scale synthesis, and facile derivation of the annulation products. The transformation is one of the few examples in which challenging sp 2 C−H bonds of CF 3 -ketimines have been functionalized. The rapid assembly of biologically important fluorinated β-amino esters by this strategy will benefit the related studies and inspire a new approach for fluorinated motif synthesis.T he assembly of fluorinated analogues of biological molecules, such as sugars, nucleosides, steroids, amino acids, and others, has become an emerging area for organic chemists (Scheme 1). 1 The growing concern should be mainly ascribed to substantially altered performances such as metabolic stability, binding affinity, solubility, and lipophilicity, compared to those of the parent counterparts, which are endowed by the unique properties of fluorine. In the case of fluorinated amino acids (F-AAs), they have four dimensions of important applications in biologically chemistry: (1) exhibiting important biologically properties such as antiviral and antitumor activities that lead to medical applications, (2)
We report a selectivity‐switchable nickel hydride‐catalyzed methodology that enables the stereocontrolled semi‐reduction of internal alkynes to E‐ or Z‐alkenes under very mild conditions. The proposed transfer semi‐hydrogenation process involves the use of a dual nickel/photoredox catalytic system and triethylamine, not only as a sacrificial reductant, but also as a source of hydrogen atoms. Mechanistic studies revealed a pathway involving photo‐induced generation of nickel hydride, syn‐hydronickelation of alkyne, and alkenylnickel isomerization as key steps. Remarkably, mechanistic experiments indicate that the control of the stereoselectivity is not ensuing from a post‐reduction alkene photoisomerization under our conditions. Instead, we demonstrate that the stereoselectivity of the reaction is dependent on the rate of a final protonolysis step which can be tuned by adjusting the pKa of an alcohol additive.
An unprecedented 1,3-dipole cycloaddition
between acyclic CF3-ketimines and N-benzyl
azomethine ylide
has been allowed by tungsten catalysis, furnishing a range of novel
imidazolidines bearing a trifluoromethylated tetrasubstituted carbon
center. This reaction appears as one of rare examples that challenging
acyclic CF3-ketimines have been engaged in 1,3-cycloaddition
reactions. The capability for gram-scale synthesis and variant derivatizations
of cycloaddition adducts illustrates the synthetic potential of this
approach. This protocol provides a facile access to a rapidly enlarging
pool of motifs with a trifluoromethylated fully substituted carbon.
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