Synthesis of a chiral N-heterocyclic carbene bearing a m-terphenyl-based phosphate moiety as an anionic N-substituent and its application to copper-catalyzed enantioselective boron conjugate additions
作者:Tomohiro Iwai、Yuki Akiyama、Masaya Sawamura
DOI:10.1016/j.tetasy.2013.05.013
日期:2013.6
A chiralN-heterocycliccarbene (NHC) ligand 1a bearing a m-terphenyl-based phosphate moiety as an anionic N-substituent has been developed. A rhodium complex [Rh(1a)(cod)]2 was synthesized and its structure was characterized by NMR and ESI-MS spectroscopy. This ligand gave high enantioselectivities in copper-catalyzed enantioselective boron conjugate additions to an α,β-unsaturated ester to give a
2′-dihydroxybiphenyl. Sulfonation of the ligands led to water soluble agents. These ligands offer an alternative to synthetic hydroxamate or catecholate siderophores. The hexamethoxylated tripodal precursors and their completing ability towards alkali cations are also described. The complexing abilities of hexahydroxylated sequesteringagents towards iron(III) are comparable to those of hydroxamate siderophores but