More sustainable use of chemical resources is part of the UN Agenda 2030. That is why chemists in synthetic products work to design and conduct efficient syntheses. In the arsenal of the synthetic organic chemist, the processes that bind several molecules (binding partners) in one step – the so-called multicomponent reactions (MCR) – play a central role. They are considered sustainable and environmentally friendly technologies for the rapid production of complex structures and drugs in one step of reaction. A team of researchers led by chemistry professor Frank Glorius (University of Münster, Germany) and Dr. Huang-Ming Huang (University of Münster and Shanghai Technical University, China) managed to use so-called ketyl radicals for the first time. MCR. This study was published in the recently founded journal Nature Synthesis.
Ketyl radicals are very important species in synthetic chemistry. They are often used in the synthesis of complex natural products. However, catalytic chemical transformations that use ketyl radicals remain a challenge. Their formation often requires “harsh” high temperature reaction conditions. Radicals can also be non-selective in their reaction pathways, which means they are difficult to control, “explains Huang-Ming Huang.
The research team used ketyl radicals and a palladium catalyst excited by visible light to create an MCR between several bonding partners. In selecting binding partners (aldehydes, 1,3-dienes and various nucleophiles), the researchers took into account various aspects: Which substances are needed for the reaction to proceed, which are readily available and which products are useful?
“We were able to tame the ketyl-type radicals by combining visible light with small amounts of commercially available palladium catalyst,” said co-author Peter Bellotti. “This easy-to-use, redox-neutral and thus environmentally friendly approach can become a common platform for building so-called complex homoalyl alcohol motifs, a commonly used structural motif in synthetic chemistry. The one-step synthesis of key intermediates that could be further transformed into valuable products is proof of the flexibility of this approach. “
In addition to the synthetic capabilities of this method, the team explores mechanistic subtleties using a combined experimental mechanistic analysis and functional density theory (DFT) calculations. “We anticipate that the combination of visible light with transition metals such as palladium may inspire further unintended synthetic transformations beyond established catalyzed reactions,” Frank Glorius concluded.
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