Phospholane-oxazoline ligands

Scheme 59 Preparation of TangPhos ligand 186 and phospholane-oxazoline ligands 188...

The enantioselective deprotonation of 128 and oxidative addition of the carbanion with Cu(II) afforded TangPhos disulfide as a mixture of diaster-eomers where the chiral C2-symmetric product was the major compound (66% de, 95% ee). A single recrystallisation afforded the desired optically pure TangPhos sulfide in 20% yield. The desulfuration was performed with hexa-chlorodisilane to yield the very air-sensitive Tangphos diphosphine in 88% yield. The synthesis of a family of phospholane-oxazoline ligands started with the preparation of carboxylic acid 129 by the proeedure in 40% yield after recrystallisation. The crude product was obtained in relatively low optical... 

The ligand synthesis is straightforward, using amino alcohols as the source of chirality in the oxazoline ring, whereas the stereochemistry in the phospholane ring is controlled by an enantioselective deprotonation using sparteine (Scheme 29.2). 

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