Studies into the Stereoselectivity of Diels-Alder Reactions with n6- Ruthenium Arene Complex Substituents
In organic chemistry, n6-ruthenium arene complexes are able to act as powerful electron-withdrawing groups, thereby facilitating the nucleophilic aromatic substitution and deprotonation of benzylic and aromatic positions.1–7 Additionally, having the metal complex bound to a non-symmetrical arene provides a source of chirality, allowing for stereoselective chemistry.1,6,8–18 It is well known that Diels-Alder (DA) reactions with an electron-rich diene can be accelerated by electron-withdrawing substituents on the dienophile. Previous studies by the Hitt research group have suggested that ?6-ruthenium arene complexes can accelerate DA reactions involving adjacent alkenes.19 However, the effect of using a chiral ruthenium arene substituent on the dienophile as a stereocontrol element has not been analyzed. In this vein, the compound [CpRu(?6-(ethyl 2-chlorocinnamate))]PF6 was synthesized in several steps from 2-chlorobenzaldehyde and used as a model dienophile in the DA reaction with 2,3-dimethyl-1,3-butadiene. Herein, we report the details of the dienophile synthesis and our attempts at a successful DA reaction.