Abstract
Phosphinooxazoline (PHOX) ligands are an important class of ligands in asymmetric catalysis. We synthesized ten novel D-fructose-derived spiro-fused PHOX ligands with different steric and electronic demand. The application of two of them was tested in asymmetric allylic alkylation. The ligands are prepared in two steps from readily available 1,2-O-isopropylidene protected β-D-fructopyranoses by the BF3·OEt2-promoted Ritter reaction with 2-bromobenzonitrile to construct the oxazoline moiety followed by Ullmann coupling of the resulting aryl bromides with diphenylphosphine. Both steps proceeded mostly in good to high yields (57–86% for the Ritter reaction and 35–89% for the Ullmann coupling). The Ritter reaction gave two anomers, which could be separated by column chromatography. The prepared ligands showed promising results (er of up to 84:16) in Tsuji–Trost reactions with diphenylallyl acetate as model substrate.
Highlights
The vast majority of biologically active compounds like vitamins and natural products occur as single enantiomers in nature
Phosphinooxazoline (PHOX) ligands are an important class of ligands in asymmetric catalysis
We synthesized ten novel D-fructose-derived spiro-fused PHOX ligands with different steric and electronic demand
Summary
The vast majority of biologically active compounds like vitamins and natural products occur as single enantiomers in nature. We synthesized ten novel D-fructose-derived spiro-fused PHOX ligands with different steric and electronic demand. The ligands are prepared in two steps from readily available 1,2-O-isopropylidene protected β-D-fructopyranoses by the BF3·OEt2-promoted Ritter reaction with 2-bromobenzonitrile to construct the oxazoline moiety followed by Ullmann coupling of the resulting aryl bromides with diphenylphosphine.
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