Exploiting the Chiral Ligands of <i>Bis</i>(imidazolinyl)- and <i>Bis</i>(oxazolinyl)thiophenes—Synthesis and Application in Cu-Catalyzed Friedel–Crafts Asymmetric Alkylation

oleh: Mohammad Shahidul Islam, Abdullah Saleh Alammari, Assem Barakat, Saeed Alshahrani, Matti Haukka, Abdullah Mohammed Al-Majid

Format: Article
Diterbitkan: MDPI AG 2021-12-01

Deskripsi

Five new <i>C</i><sub>2</sub>-symmetric chiral ligands of 2,5-<i>bis</i>(imidazolinyl)thiophene (<b>L1</b><b>–L3</b>) and 2,5-<i>bis</i>(oxazolinyl)thiophene (<b>L4</b> and <b>L5</b>) were synthesized from thiophene-2,5-dicarboxylic acid (<b>1</b>) with enantiopure amino alcohols (<b>4a</b>–<b>c</b>) in excellent optical purity and chemical yield. The utility of these new chiral ligands for Friedel–Crafts asymmetric alkylation was explored. Subsequently, the optimized tridentate ligand <b>L5</b> and Cu(OTf)<sub>2</sub> catalyst (15 mol%) in toluene for 48 h promoted Friedel–Crafts asymmetric alkylation in moderate to good yields (up to 76%) and with good enantioselectivity (up to 81% <i>ee</i>). The <i>bis</i>(oxazolinyl)thiophene ligands were more potent than <i>bis</i>(imidazolinyl)thiophene analogues for the asymmetric induction of the Friedel–Crafts asymmetric alkylation.