Towards chiral 3-phenyl-tetrahydroquinolines through iridium catalyzed asymmetric hydrogenation

Abstract

Asymmetric catalysis has had an impact over more than half a century, due to the fact that it is one of the most efficient methods to prepare chiral organic compounds. When it comes to asymmetric hydrogenation, Pfaltz demonstrated that introducing iridium as the metal centre in phosphinooxazolines ligands was very efficient, especially with a bulky non-coordinating anion such as BArF. Inspired by this, our group has been working on a new catalyst, Ir-(S)P-DTP, whose structure bears a phosphinooxazoline ligand derived from threonine, in which a P-stereogenic centre has been introduced in order to increase the performance of the catalyst. This new catalyst has shown excellent conversion and enantiomeric excess for β,γ-substituted allylic carbamates. In this project, allylic carbamates have been synthesized and submitted to asymmetric hydrogenation with the Ir-(S)P-DTP catalyst to extend the scope. Two of have provided total conversion and excellent enantiomeric excess. An allylic carbamate with an ortho-chloride in the terminal phenyl ring has also been synthesized and submitted to asymmetric hydrogenation, providing successful results as well. Additionally, the compound with an ortho-chloride has been tested in the intramolecular Buchwald-Hartwig reaction to yield the corresponding chiral 3-phenyl-tetrahydroquinoline