Synergistic use of electrochemistry and organometallic
catalysis
has emerged as a powerful tool for site-selective C–H functionalization,
yet this type of transformation has thus far mainly been limited to
arene C–H functionalization. Herein, we report the development
of electrochemical vinylic C–H functionalization of acrylic
acids with alkynes. In this reaction an iridium catalyst enables C–H/O–H
functionalization for alkyne annulation, affording α-pyrones
with good to excellent yields in an undivided cell. Preliminary mechanistic
studies show that anodic oxidation is crucial for releasing the product
and regeneration of an Ir(III) intermediate from a diene-Ir(I) complex,
which is a coordinatively saturated, 18-electron complex. Importantly,
common chemical oxidants such as Ag(I) or Cu(II) did not give significant
amounts of the desired product in the absence of electrical current
under otherwise identical conditions.
A new method for C-C and C-N bond formation of heteroaromatics and C(sp(3))-H alkanes was developed with high regioselectivity. The reaction occurred on C8 to give 8-cylcoakylpurines by C-C bond formation only promoted by tBuOOtBu, while it occurred on the amino group to give N6-alkylated purines by C-N bond formation when 2 equiv of CuI were added. A reaction mechanism was also proposed based on our preliminary experimental data.
The asymmetric direct aldol reactions of a wide scope of aldehydes with unmodified ketones in the presence of 20 mol%(S,S,S)-pyrrolidine-2-carboxylic acid (2'-hydroxyl-1',2'-diphenyl-ethyl)-amine (1) were performed in ionic liquids; aldol products with 91 to >99% ees for aromatic aldehydes and 99% ees for alphatic aldehydes were offered by the present procedure.
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