Many optically active compounds exhibit important and desirable biological properties. One way of carrying out enantioselective reactions to produce optically pure compounds is the use of chiral catalysts. Among many catalysts, transition metal complexes with different types of chiral ligands play a very important role. Bisphosphine ligands are among the most important class of ligands used in transition metal catalysis. The search for new structures of ligands and complexes and their use in stereocontrolled reactions is an important direction of research. An important aspect in the search for new ligands is the use of natural, renewable and easily accessible chiral precursors. Monoterpenes, especially alpha-pinene and camphor, fill these rules very well. In our previous studies, we have shown that the use of a rigid bicyclic pinane structure as a framework for the construction of chiral spiroborate esters1 or PHOX2 ligands gives good results.
Herein, we present the new approach to the synthesis of rigid bicyclic chiral bisphosphines derived from α-pinene. Thus, α-pinene is transformed into isopinocamphone or verbanone and these ketones are converted to spiroepoxides. Controlled reduction of epoxides with borane gives allylic alcohols, which are transformed into bisphosphines by previously developed methods.
We wish to thank for the financial support from National Science Centre Preludium 4 No. 2012/07/N/ST5/02194.
1 Ćwiklińska M., Krzemiński M. P., Tafelska-Kaczmarek A., Tetrahedron: Asymmetry 2015, 26, 1453-1458.
2 Kmieciak A., Krzemiński M. P., Tetrahedron: Asymmetry 2017, 28, 467-472.