Abstract
A series of mixed oxides of CuO, CeO2, and SiO2 were prepared by gel combustion and employed for the first time as efficient solid catalysts in a solvent-less liquid-phase cross-dehydrogenative coupling. The facile one-pot catalyst synthesis resulted in highly porous materials presenting large specific surface areas and strong metal–support interactions. The interaction with highly dispersed CeO2 enhanced the redox properties of the CuO species. The CuO-CeO2-SiO2 composites exhibited excellent catalytic performance for the selective coupling between 1,1-diphenylethylene and tetrahydrofuran with a yield up to 85% of 2-(2,2-diphenylvinyl)-tetrahydrofuran in the presence of di-tert-butyl peroxide (DTPB) and KI. Albeit both CuO and CeO2 species are proved to be responsible for the catalytic conversion, a great synergistic improvement in the catalytic activity was obtained by extended contact between the oxide phases by high porosity in comparison with the reactions using individual Cu or Ce catalysts. The activity of the composite catalyst was shown to be highly stable after five successive reaction cycles. Furthermore, the study scope was extended to the synthesis of different derivatives via composite-catalyzed coupling of C(sp2)-H with C(sp3-H) adjacent to a heteroatom. The good yields recorded proved the general validity of this composite for the cross-dehydrogenative coupling reaction rarely performed on solid catalysts.
Highlights
Cross-dehydrogenative coupling (CDC) to directly build a C-C bond from two simple C-H bonds has emerged as an attractive goal in organic synthesis [1,2]
Offering great benefits including improving atom economy, step efficiency, and reducing cost and waste, the cross-dehydrogenative coupling (CDC) reaction is a more efficient synthetic protocol to access product molecules compared to traditional cross-couplings, which often require the use of prefunctionalized halides and organometallic reagents [1,3,4,5]
Α-C(sp3 )–H of ethers and amines can be selectively coupled with C(sp3 )–H or C(sp2 )–H, leading to more complex structural motifs which have been usually found in natural products, pharmaceuticals, agrochemicals, biologically active molecules, and functional materials [6,7,8]
Summary
Offering great benefits including improving atom economy, step efficiency, and reducing cost and waste, the CDC reaction is a more efficient synthetic protocol to access product molecules compared to traditional cross-couplings, which often require the use of prefunctionalized halides and organometallic reagents [1,3,4,5]. Α-C(sp3 )–H of ethers and amines can be selectively coupled with C(sp3 )–H or C(sp2 )–H, leading to more complex structural motifs which have been usually found in natural products, pharmaceuticals, agrochemicals, biologically active molecules, and functional materials [6,7,8]. The. CDC for the α-functionalization of ethers and amines is still a grand challenge because of the inert and ubiquitous nature of the C(sp3 )–H bond. The FeCl3 - or CoCl2 -catalyzed CDC between α-C(sp3 )–H of ethers and C(sp2 )–H of coumarin derivatives has been reported [5,14]
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