Siloxane-Supported Bisoxazoline Ligands

Significance

The development of insoluble polymer-supported chiral bisoxazoline (Box) ligand was described. Thus, the Box-bearing terminal alkene 1 was treated with PMHS in the presence of Pt catalyst to give the soluble polymeric Box 2 (eq. 1). The soluble polymer 2 was cross-linked with PDMS via Pt-catalyzed hydrosilylation, and the residual Si-H was capped with 1-hexadecene to afford the insoluble polymer-supported Box 3. The Mukaiyama aldol reaction of silyl enolate 4 with 5 was conducted in the presence of 3 and Cu(OTf)₂ in THF at 0 °C for 2 hours to give the aldol product 6 in 98% yield and 93% ee (eq. 2). The cyclopropanation of isobutene 7 with ethyl diazoacetate 8 was performed in the presence of 3 and Cu(OTf)₂ in hexane at 0 °C for 4 hours to give the cyclopropane 9 in 91% yield with 95% ee (eq. 3).