Abstract
AbstractStarting from (R)‐Ugi's amine, diastereoselective lithiation followed by Ar'PCl2 and then Ar’’MgBr led to the generation, as single diastereoisomers, of (R,Sp,Sphos) [Ar’=Ph, Ar’’=o‐Tol] and (R,Sp,Rphos) [Ar’=o‐Tol, Ar’’=Ph] PPFA ligand derivatives. Amine substitution of both with HPCy2 gave P‐stereogenic Josiphos ligands, and then addition of CuCl, the corresponding copper(I) complexes. The latter were also generated by using borane P and N protecting groups and in situ Cu(I) complexation, avoiding the isolation of air‐sensitive phosphine intermediates. This protection methodology was also applied to the synthesis of Josiphos/CuCl complexes derived from PCl3. In addition, related bulky cobalt‐sandwich complex‐based derivatives were also obtained. Preliminary investigation revealed isolated CuCl complexes as competent catalyst precursors for enantioselective conjugate addition reactions.
Highlights
Many ligands have been developed for application in asymmetric synthesis, relatively few have found widespread use
We chose to explore this aspect of ligand-optimisation by first synthesising a series of readily isolated and air-stable copper(I) chloride complexes C (Ar’ 1⁄46 Ar’’ and Ar’ = Ar’’)
As in our previous report, our aim was to control the introduction of phenyl and o-tolyl groups to create the phosphorus-based stereogenic centre
Summary
Many ligands have been developed for application in asymmetric synthesis, relatively few have found widespread use Of these so-called ‘privileged’ ligands,[1] one of the most successful class are the ferrocene-based Josiphos ligands A.[2] Numerous derivatives are known, obtained by varying the identity of R’ and R’’, and many are commercially available. In addition to e.e. optimisation by varying the steric and electronic properties of the R’ and R’’ substituents, there is the possibility of creating an additional phosphorus-based stereogenic centre, such that one of the two resulting diastereomeric ligands B may lead to higher enantioslectivity.[7] We chose to explore this aspect of ligand-optimisation by first synthesising a series of readily isolated and air-stable copper(I) chloride complexes C (Ar’ 1⁄46 Ar’’ and Ar’ = Ar’’)
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