Abstract
ABSTRACTAn approach to the synthesis of libraries of chiral phosphine ligands is described, using condensations of 2-formylarylboronic acids, diols or related compounds, and aminophosphines. The three-component nature of this condensation, along with the ready availability of the building blocks, enables the rapid generation of diverse structures. From a library of iminoboronate-derived phosphines, three ligands that gave 90% ee or greater in a benchmark palladium-catalyzed allylic substitution reaction were identified. Significant variation of selectivity as a function of the structure of each component was observed. 11B NMR spectroscopy was used to evaluate the existence of B–N interactions in the free ligands as well as their Pd-derived complexes. A bidentate P,N-coordination mode was inferred for ligands that gave high enantioselectivity in the allylic substitution reaction.Abbreviation: BINOL: 1,1'-bi-2-naphthol; BSA: N,O-bis(trimethylsilyl)acetamide; DIOP: (2,3-O-isopropylidene-2,3-dihydroxy-1,4-bis(diphenylphosphino)butane; HPLC: high-performance liquid chromatography; NMR: nuclear magnetic resonance; THF: tetrahydrofuran
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