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Synfacts 2006(1): 0039-0039
DOI: 10.1055/s-2005-921740
DOI: 10.1055/s-2005-921740
Metal-Catalyzed Asymmetric Synthesis and Stereoselective Reactions
© Georg Thieme Verlag Stuttgart · New York
N-Heterocyclic Carbenes for Conjugate Additions of Arylboronic Acids
J.-M. Becht, E. Bappert, G. Helmchen*
Universität Heidelberg, Germany
Further Information
Publication History
Publication Date:
16 December 2005 (online)
Significance
An air and moisture tolerant N-heterocyclic carbene (NHC) catalyst for the conjugate addition of arylboronic acids is described. This catalyst provides an improved procedure for the synthesis of a GABA analogue with the key addition adduct being produced with 99% ee. Enones with various ring sizes were tested and cyclohexenone gave the high enantioselectivies (>94% ee) while cyclopentenone and cycloheptenone were obtained in lower enantioselectivities (<90% ee). Importantly, both electron-withdrawing and electron-donating substituents on the arylboronic acid showed very high selectivity (>94% ee for addition to cyclohexenone).