A novel copper supported on hydromagnesite
(Cu/HM) nanomaterial
was prepared by a simple impregnation method at room temperature and
characterized by PXRD, SEM, TEM, EDAX, XPS, ICP-AES and FT-IR techniques.
The EDAX and XPS results revealed the presence of 8.82 wt % of copper
in (+2) oxidation state. Three-component coupling of ketone and amine
with alkyne to afford tetrasubstituted propargylamine is known as
KA2 coupling, whereas the three-component reaction of aldehydes and
amine with alkyne to give propargylamine is considered as an A3-coupling
reaction. The Cu/HM was found to be an efficient heterogeneous catalyst
for KA2 coupling reaction under solvent free condition, and A3 coupling
strategy to afford the pyrrolo[1,2-a]quinolines in
DEG as a green solvent. The high catalytic activity of Cu/HM in the
A3 coupling strategy to afford propargylamine intermediate is due
to the synergistic effect of both Cu2+ and Mg2+ active sites. The versatility of Cu/HM catalyst was also studied
for the decarboxylative A3 and KA2 coupling strategies. The present
method offers several advantages such as simple procedure for the
catalyst preparation, versatile catalytic applications, cheap precursors,
higher yield of products in short reaction time, recovery and reusability
of the catalyst.
A green
approach for decarboxylative C(sp3)–H
activation of proline amino acid was accomplished by coupling with
aldehydes and alkynes to afford α-alkynylated N-substituted
pyrrolidines as value-added synthons using reduced graphene oxide
supported copper oxide (RGO@CuO) nanocatalysts. The RGO@CuO nanocomposites
were obtained by the impregnation of micrometer-sized malachite spheres,
as a renewable and sustainable copper mineral precursor, on the graphene
oxide (GO) sheets followed by calcination at 300–450 °C
for 5 h. The characterization of as-synthesized composites revealed
the generation of monodispersed and uniformly embedded copper oxide
(CuO) nanoparticles with sizes ranging from 10 to 15 nm on RGO thin
sheets via GO as a support as well as indirect template for dissembling
and decomposition of micrometer-sized malachite spheres. The RGO@CuO
composites were found to be efficient and robust nanocatalysts compared
with CuO nanoparticles (NPs) alone. The present method offers several
advantages, such as wide substrate scope, and avoids the usage of
excess equivalent of substrates with minimal waste generation (E-factor
= 0.24) and high reaction mass efficiency (80.7%), and the nanocatalyst
was recycled for five times without significant loss in its activity
with a negligible leaching of CuO NPs from RGO sheets.
C1-alkynylation of tetrahydroisoquinoline (THIQ) with wide substrate scope was achieved via A3 coupling strategy from the reaction among THIQ, aldehydes and alkynes using CuO@Fe2O3 as a nanocatalyst under green reaction conditions.
Multi-metallic hybrid nanocatalysts consisting of a porous metal oxide host and metal satellite guests serve as a heterogeneous interface for multi-step transformations of divergent and energy-challenging substrates.
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