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Abstract In the presence of a thiourea–carboxylic acid catalyst, N-9-fluorenyltryptamines undergo highly enantioselective Pictet–Spengler reactions with a range of aldehydes. The reaction works particularly well with aromatic aldehydes, tolerating electronically diverse substituents in all ring positions. Electron-deficient tryptamines are viable substrates. Removal of the fluorenyl protecting group is readily accomplished without deterioration of product ee.
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Zirconium-catalyzed asymmetric Kabachnik–Fields reactions of aromatic and aliphatic aldehydes
An effective catalyst has been developed for the three-component reaction of aldehydes, anilines and phosphites in an asymmetric catalytic Kabachnik–Fields reaction to give α-aminophosphonates. A catalyst was sought that would give high asymmetric inductions for aromatic and, and more particularly, for aliphatic aldehydes since there has not previously been an effective catalyst developed for this class of aldehydes. The optimal catalyst is prepared from three equivalents of the 7,7′-di- t -butylVANOL ligand, one equivalent of N -methylimidazole and one equivalent of zirconium tetraisopropoxide. This catalyst was most efficient in the presence of 10 mol% benzoic acid. Optimal conditions for aryl aldehydes required the use of 3,5-diisopropyl-2-hydroxyaniline and gave the aryl α-aminophosphonates in up to 96% yield and 98% ee over 11 different aryl aldehydes. The best aniline for aliphatic aldehydes was found to be 3- t -butyl-2-hydroxyaniline and gave the corresponding phosphonates in up to 83% yield and 97% ee over 18 examples. The asymmetric inductions for aliphatic aldehydes were comparable with those for aromatic aldehydes with a mean induction of 90% ee for the former and 91% ee for the latter. The best method for the liberation of the free amine from the aniline substituted α-aminophosphonates involved oxidation with N -iodosuccinimide.
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- Award ID(s):
- 1856335
- PAR ID:
- 10301983
- Date Published:
- Journal Name:
- Chemical Science
- Volume:
- 12
- Issue:
- 37
- ISSN:
- 2041-6520
- Page Range / eLocation ID:
- 12333 to 12345
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/d1sc03222d
