An immobilized monophosphine-Ir system, which was prepared in situ from [Ir(OMe)(cod)](2) and a silica-supported, compact phosphine, showed high activities and selectivities for the borylation of aromatic C-H bonds with bis(pinacolato)diboron. This system was effective not only for the borylation of benzene but also for the ortho borylation of arenes with directing groups, such as ester, amide, sulfonate, acetal, alkoxymethyl, and chloro groups, under mild reaction conditions.
We
found that N-heterocyclic carbene catalysis
promoted the unprecedented decarboxylative coupling of aryl aldehydes
and tertiary or secondary alkyl carboxylic acid-derived redox-active
esters to produce aryl alkyl ketones. The mild and transition-metal-free
reaction conditions are attractive features of this method. The power
of this protocol was demonstrated by the functionalization of pharmaceutical
drugs and natural product. A reaction pathway involving single electron
transfer from an enolate form of Breslow intermediate to a redox ester
followed by recombination of the resultant radical pair to form a
carbon–carbon bond is proposed.
Supported phosphine-Rh systems, prepared in situ from silica-supported bridgehead monophosphines and [Rh(OH)(cod)](2), have enabled ortho-selective C-H borylation for a range of arenes containing nitrogen-based directing groups. The regioselectivity was excellent with various N-directing groups, including saturated and unsaturated N-heterocycles, tert-aminoalkyl groups, and imine-type C-N double bonds. The reaction showed significant tolerance toward steric repulsion around the reacting C-H bond. This Rh catalysis complements the Ir-catalyzed ortho-borylation, which is effective for arenes with oxygen-based directing groups.
The N-heterocyclic carbene-catalyzed radical relay
enables the vicinal alkylacylation of styrenes, acrylates and acrylonitrile
using aldehydes and tertiary alkyl carboxylic acid-derived redox-active
esters. This protocol introduces tertiary alkyl groups and acyl groups
to C–C double bonds with complete regioselectivity to produce
functionalized ketone derivatives. The radical relay mechanism involves
single electron transfer from the enolate form of a Breslow intermediate
and radical addition of the resultant alkyl radical to the alkene
followed by radical–radical coupling.
This
manuscript reports a visible-light-mediated organosulfide
catalysis that enables the decarboxylative coupling between simple
aliphatic alcohol and tertiary or secondary alkyl carboxylic acid-derived
redox active esters to produce a C(sp3)–O–C(sp3) fragment. Results of the coupling using other heteroatom
nucleophiles such as water, amides, and thiols are also described.
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