Tropanes as Scaffolds for Phosphorus–Olefin Ligands and Their Application in Asymmetric Catalysis1. Issue 8 (6th February 2013)

• Record Type: Journal Article
• Authors: Vlahovic, Sandra; Schädel, Nicole; Tussetschläger, Stefan; Laschat, Sabine
• Is Part Of: European journal of organic chemistry. Issue 8(2013)
• Page Start: 1580
• Page End: 1590
• Publication Date: 2013-02-06
• Subjects: Asymmetric catalysis -- Trop­anes -- Michael addition -- Alkene ligands -- P ligands -- Ligand effects; Chemistry, Organic -- Periodicals; Organic compounds -- Synthesis -- Periodicals; Bioorganic chemistry -- Periodicals; Chemistry, Physical organic -- Periodicals; 547
• DOI: 10.1002/ejoc.201201539
• Languages: English
• ISSNs: 1434-193X

Abstract

Abstract: Tropane‐derived phosphorus–olefin hybrid ligands bearing various combinations of P‐units (chiral BINOL‐derived units/achiral PPh2 ‐units) with a tropene skeleton (chiral/achiral) have been synthesized and used in Cu‐catalysed conjugate 1, 4‐additions of diethylzinc to cyclic enones and in Rh‐catalysed 1, 4‐additions of phenylboronic acid (Hayashi–Miyaura reaction) with cyclic and acyclic enones. Whereas in Cu‐catalysed reactions only moderate yields and ee values (up to 49 % ee ) were obtained, up to 97 % ee was observed in the Hayashi–Miyaura reaction with various substrates. The most promising results in both reactions were achieved with ligands11 and15, which contain a chiral alkene/achiral P‐unit or an achiral alkene/chiral P moiety, respectively, and where the metal is complexed on the exo side of the tropene skeleton. In contrast, ligands with an endo coordination mode showed only low (13 ) or no activity (12 ) in all of the 1, 4‐additions. NMR and ESI‐MS experiments revealed the presence of two cationic [Rh I (15 )2 ] + species in solution. Abstract : It's the combination! Different types of P/alkene hybrid ligands combining chiral tropanes with P‐units were prepared. Depending on the position of the phosphorus unit, coordination of the metal atom is favoured either on the exo or endo side. The successful use of the ligands in Cu‐ and Rh‐catalysed conjugate additions is described.