Synthesis 2015; 47(06): 789-800
DOI: 10.1055/s-0034-1379877
paper
© Georg Thieme Verlag Stuttgart · New York

Synthesis of New Camphor-Based Carbene Ligands and Their Application in a Copper-Catalyzed Michael Addition with B2Pin2

Maximilian Koppenwallner
,
Eduard Rais
,
Magdalena Uzarewicz-Baig
,
Sobia Tabassum
,
Mazhar Amjad Gilani
,
René Wilhelm*
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Publikationsverlauf

Received: 16. September 2014

Accepted after revision: 25. November 2014

Publikationsdatum:
22. Dezember 2014 (online)


Abstract

In this work the synthesis of new asymmetric camphor-based carbene ligands from camphoric acid is described. The new carbenes can be prepared directly in high yields by the sequence: regioselective arylation of the less hindered primary amine group of (+)-cis-1,2,2-trimethylcyclopentane-1,3-diamine by Buchwald–Hartwig amination, treatment with trimethyl orthoformate, and finally treatment with a benzylic halide. The resulting carbenes, incorporating an aryl and a benzylic substituent, were successfully applied as ligands in a copper-catalyzed B2Pin2 [bis(pinacolato)diboron] addition to an unsaturated carbonyl compound. Depending on the substituents dual stereocontrol was observed and one enantiomer was obtained in up to 82% ee and the opposite enantiomer in up to 78% ee.

Supporting Information