Preparation of Ionic Liquid Supported Organocatalysts for the Synthesis of Stereoselective (R)-9-Methyl-5(10)-octaline-1,6-dione

Abstract

The synthesis of Proline-2-triethyl-ethylamide hexafluorophosphate (ILPA-PF6) (with 96% yield) and further the application during the synthesis of (R)-9-Methyl-5(10)-octaline-1,6-dione (Wieland–Miescher ketone molecule) are defined in this manuscript. The suggested protocol signifies one of the most efficient methods for the synthesis of these flexible chiral building blocks in good yield. The evident solubility of ionic liquids allows straightforward isolation of the (R)-9-Methyl-5(10)-octaline-1,6-dione product from reaction mass. Additionally, six times catalyst recycling was considered the main conclusion of this proposed procedure. We report the synthesis of a triethyl salt anchored pyrrolidine amide organocatalyst. The route for the synthesis of Proline-2-triethyl-ethylamide hexafluorophosphate ionic liquid is described in Scheme 1. In the first part of the synthesis commercially available Boc-proline, was allowed to react with 2-bromo-ethylamine hydrobromide to obtain N-Boc-proline-2-bromo-ethylamide. Subsequent alkylation of triethylamine with N-Boc-proline-2-bromo-ethylamide gave N-Boc-proline-2-triethyl-ethylamide bromide in 92% yield. After the Boc deprotection step and subsequent anion exchange in water with KPF6, afforded the desired air-stable pale-yellow and transparent Proline-2-triethyl-ethylamide hexafluorophosphate ionic liquid (Proline-2-triethyl-ethylamide hexafluorophosphate, ILPA-PF6) with 97% yield. None