Microwave Mediated Stereoselective Chelation-Controlled Heck-Reactions

Stefanie Schlummer, Jonas Sävmarker, Peter Nilsson and Mats Larhed, Uppsala University

Abstract
Palladium-catalyzed coupling reactions of the Heck type have emerged as one of the most versatile carbon-carbon bond forming processes. However, despite the extensive use of the Heck coupling, the reaction still suffers from some limitations such as unsatisfactory control of stereoselectivity.

One approach to circumvent this problem is the use of chiral auxiliaries. Thus, an efficient coordination of the oxidative addition complex to the auxiliary helps to enhance the stereoselectivity in the reaction.

Previous attemps by Hallberg et al. succeeded in the arylation of a cyclopentanone derivative where the stereoselectivity was controlled by internal chelation of the aryl palladium complex with (S)-methylpyrrolidine as a chiral auxiliary. This methodology has now been further investigated.

Highly stereoselective arylations of a chelating prolinol vinyl ether can be performed using aryl iodides as well as aryl bromides, utilizing either conventional or microwave mediated heating.

Beside the highly efficient methylpyrrolidine moiety, the effect of various chelating groups was studied. Furthermore, we could successfully demonstrate that the use of high-density microwave irradiation tremendously accelerates the reaction rates, providing higher yields and cleaner pathways.

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