Supramolecular-induced regiocontrol over the photochemical [4 + 4] cyclodimerization of NHC- or azole-substituted anthracenes

Thanks to the impressive control that microenvironments within enzymes can have over substrates, many biological reactions occur with high regio- and stereoselectivity. However, comparable regio- and stereoselectivity is extremely difficult to achieve for many types of reactions, particularly photoc...

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Published in:Chemical science (Cambridge) 2020-12, Vol.12 (6), p.2165-2171
Main Authors: Bai, Sha, Ma, Li-Li, Yang, Tao, Wang, Fang, Wang, Li-Feng, Hahn, F. Ekkehardt, Wang, Yao-Yu, Han, Ying-Feng
Format: Article
Language:English
Subjects:
Anthracene
Assemblies
Chemistry
Crystallography
Cycloaddition
Irradiation
Photochemical reactions
Stereoselectivity
Substitutes
Substrates
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Summary:Thanks to the impressive control that microenvironments within enzymes can have over substrates, many biological reactions occur with high regio- and stereoselectivity. However, comparable regio- and stereoselectivity is extremely difficult to achieve for many types of reactions, particularly photochemical cycloaddition reactions in homogeneous solutions. Here, we describe a supramolecular templating strategy that enables photochemical [4 + 4] cycloaddition of 2,6-difunctionalized anthracenes with unique regio- and stereoselectivity and reactivity using a concept known as the supramolecular approach. The reaction of 2,6-azolium substituted anthracenes H 4 - L (PF 6 ) 2 ( L = 1a-1c ) with Ag 2 O yielded complexes anti -[Ag 2 L 2 ](PF 6 ) 4 featuring an antiparallel orientation of the anthracene groups. Irradiation of complexes anti -[Ag 2 L 2 ](PF 6 ) 4 proceeded under [4 + 4] cycloaddition linking the two anthracene moieties to give cyclodimers anti -[Ag 2 ( 2 )](PF 6 ) 2 . Reaction of 2,6-azole substituted anthracenes with a dinuclear complex [Cl-Au-NHC-NHC-Au-Cl] yields tetranuclear assemblies with the anthracene moieties oriented in syn -fashion. Irradiation and demetallation gives a [4 + 4] syn -photodimer of two anthracenes. The stereoselectivity of the [4 + 4] cycloaddition between two anthracene moieties is determined by their orientation in the metallosupramolecular assemblies. A supramolecular templating strategy that enables the photochemical [4 + 4] cycloaddition of 2,6-difunctionalized anthracene derivatives with unique stereoselectivity has been developed based on metal-NHC units.
ISSN:2041-6520
2041-6539
DOI:10.1039/d0sc06017h