21/08/2013, by

Chemistry on the rooftop: The light of a new chemistry

Researchers at the Institute of Chemical Research of Catalonia (ICIQ) in Tarragona use sun light to generate new chiral chemical compounds in high yields with high enantioselectivity. This innovative strategy, published in Nature Chemistry, opens up new avenues for the design of new reactions in the field of photochemistry and asymmetric catalysis.

A team of scientists at the Institute of Chemical Research of Catalonia (ICIQ) has designed a new photochemical method that uses visible light from a light bulb or the sun, to activate molecules (chiral enamines) and promote the formation of new carbon bonds in a controlled manner.

Paolo Melchiorre and his team at ICIQ rooftop doing a reaction

Photochemistry is the branch of chemistry that studies the reactions that occur when atoms or molecules absorb light. This discipline is inspired by natural processes such as the formation of vitamin D, the visual cycle or the photosynthesis of plants. The molecules involved in these processes absorb light, get excited and go to a higher energy state. Then, these high-energy molecules can react with other molecules to form new chemical compounds.

This chemical discipline has the great advantage of using a clean and cheap energy source: solar energy. However, one of the major handicaps of photochemistry in asymmetric catalysis is the lack of control or selectivity in the final products.

Now, ICIQ researchers led by Paolo Melchiorre, have designed the first example of photochemical asymmetric catalysis in which the catalyst forms a complex capable of absorbing photons, or particles of light, to subsequently react in a controlled and selective way to afford new chemical compounds with well-defined three-dimensional structures.

The protocol is simple, the reaction is carried out at room temperature and the reagents are readily available. The reaction flask is illuminated with a lamp or sunlight for six and a half hours to give 89% conversions with selectivities of 94%.

‘We found a bridge to connect two very powerful fields of molecule activation such as photochemistry and asymmetric organocatalysis’ – points out Paolo Melchiorre.

The group leader expects these results to open new avenues for the design of asymmetric reactions by photochemical processes.

Reference: 

Photochemical activity of a key donor–acceptor complex can drive stereoselective catalytic a-alkylation of aldehydes
Elena Arceo, Igor D. Jurberg, Ana Álvarez-Fernández and Paolo Melchiorre
Nature Chemistry, DOI: 10.1038/NCHEM.1727

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