Alternative pathways to α,β-unsaturated ketones via direct oxidative coupling transformation using Sr-doped LaCoO ₃ perovskite catalyst

Abstract

A strontium-doped lanthanum cobaltite perovskite material was prepared, and used as a recyclable and effective heterogeneous catalyst for the direct oxidative coupling of alkenes with aromatic aldehydes to produce α,β-unsaturated ketones. The reaction afforded high yields in the presence of di-tert-butylperoxide as oxidant. Single oxides or salts of strontium, lanthanum and cobalt, and the undoped perovskite offered a lower catalytic activity than the strontium-doped perovskite. Benzaldehyde could be replaced by benzyl alcohol, dibenzyl ether, 2-oxo-2-phenylacetaldehyde, 2-bromoacetophenone or (dimethoxymethyl) benzene in the oxidative coupling reaction with alkenes. To our best knowledge, reactions between these starting materials with alkenes are new and unknown in the literature.

Combustion-Synthesized Porous CuO-CeO2-SiO2 Composites as Solid Catalysts for the Alkenylation of C(sp3)-H Bonds Adjacent to a Heteroatom via Cross-Dehydrogenative Coupling

“…However, no further enhancement in the formation of the major product was observed when increasing the reaction temperature to 140 • C. Indeed, the dehydrogenative alkenylations of ethers catalyzed by molecular Cu salts were performed at 120 • C in the earlier studies, implying that this temperature condition was not only appropriate for selective activation and coupling of C(sp 2 )-H and C(sp 3 )-H bonds but also controlled the unexpected oxidation of alkene substrates in the presence of the DTBP oxidant [13,15,80,81]. In the work on oxidative coupling, Trinh and co-workers also reported that the oxidation of 1,1-diphenylethylene to benzophenone by DTBP was significant at 140 • C [82].…”

“…These highly reactive radicals would activate the C sp3 -H bond adjacent to the oxygen atom of THF via abstracting this hydrogen atom to form a cyclic ether radical which can subsequently diffuse from the micropores to the outer surface for the reaction with the bulky 1,1-diphenylethylene molecule, yielding a benzylic-based radical [78,85]. The conversion of the radical into the desired product takes place via the oxidation by the complex [M n+1 -O t Bu] to release t BuOH and regenerate M n+ for the catalytic cycle [12,82]. The fact that adding TEMPO as a radical scavenger to the reaction led to no formation of the coupling product could strengthen this radical mechanism.…”