New Thiazoline–Oxazoline Ligands and Their Application in the Asymmetric Friedel–Crafts Reaction

Abstract

Six members of a novel non‐C2‐symmetric ligand class incorporating an oxazoline and thiazoline unit have been prepared in a four‐step, high‐yielding and convergent synthesis, in which the key step is a microwave‐assisted palladium‐catalyzed aryl amination. The new ligands induced enantiomeric excesses of up to 76 % in the asymmetric Friedel–Crafts reaction.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Synthesis of Bis(oxazoline) Ligands Possessing C-5 gem-Disubstitution and Their Application in Asymmetric Friedel–Crafts Alkylations

“…11 Catalytic Asymmetric Friedel−Crafts Reaction. The Friedel−Crafts (FC) alkylation is a cornerstone reaction in organic chemistry.…”

The Synthesis of Some New (S)-1-Aryl-N-(1-hydroxy-3-phenylpropan-2-yl)-5-methyl-1H-1,2,3-triazole-4-carboxamide

“…Identified as a compound, IR absorption of hydroxyl is showing at 3359 ~ 3478 cm ‐1 and amino at 3201 ~ 3416 cm ‐1 of 4a , 4b , 4c , 4d , 4e , 4f , 4g , 4h , 4i , 4j , as a carbonyl compound showing strong IR absorption at 1642 ~ 1661 cm ‐1 . 1 HNMR, chemical shift range of triazole‐5‐CH 3 peak is at 2.464 ~ 2.647 ppm of 4a , 4b , 4c , 4d , 4e , 4f , 4g , 4h , 4i and chemical shift range of ‐CO‐NH‐ doublet peaks is show at 7.507 ~ 8.594 ppm, J = 8.0 ~ 8.8 Hz of 4a , 4b , 4c , 4d , 4e , 4f , 4g , 4h , 4i , 4j , which are shifted to lower fields than the corresponding protons at 6.29 ppm because of the hydrogen‐bond and triazole ring induced. The chemical shift range of C H 2 Ph peak is at 2.854 ~ 3.067 ppm, chemical shift range of C H 2 O doublet peaks is show at 2.854 ~ 3.747 ppm, 2.958 ~ 3.849 ppm, chemical shift range of C H N peak is at 4.199 ~ 4.463ppm of 4a , 4b , 4c , 4d , 4e , 4f , 4g , 4h , 4i .…”

Synthesis of Thiazoline–Oxazoline Ligands and Their Application in Asymmetric Catalysis

“…The coupling of 2‐( o ‐bromophenyl)thiazoline ( 6 ) and 2‐( o ‐aminophenyl)oxazoline ( 7 ) allows a facile synthesis of a new range of sterically and electronically diverse ligands in a few high‐yielding steps. The synthesis of these coupling partners can be obtained in one and two steps, respectively, in very high yields, and microwave‐assisted coupling is preferred over coupling under thermal conditions 34…”

“…As a continuation of our study on unsymmetrical ligands, we have recently successfully applied six examples (R 1 , R 2 = i Pr, t Bu, Ph, Bn and two differentially substituted analogues R 1 = t Bu, R 2 = Bn and R 1 = Bn, R 2 = t Bu) of the mixed thiazoline–oxazoline ligand class 2 to the Friedel–Crafts alkylation of indole by using a range of nitrostyrenes, obtaining enantiomeric excess values of up to 76 % (for R 1 = t Bu, R 2 = Bn) in excellent yields 34. In an attempt to enhance the enantioselectivity induced by these thiazoline–oxazoline containing ligands in this reaction, the ligand series has now been expanded with the synthesis of 10 new analogues (i.e., 2a – j ) and their application to the Friedel–Crafts alkylation of indole with trans ‐β‐nitrostyrene.…”