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Citation
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HERO ID
5917525
Reference Type
Journal Article
Title
Unsymmetrical Diarylmethanes by Ferroceniumboronic Acid Catalyzed Direct Friedel-Crafts Reactions with Deactivated Benzylic Alcohols: Enhanced Reactivity due to Ion-Pairing Effects
Author(s)
Mo, X; Yakiwchuk, J; Dansereau, J; Mccubbin, JA; Hall, DG
Year
2015
Is Peer Reviewed?
Yes
Journal
Journal of the American Chemical Society
ISSN:
0002-7863
EISSN:
1520-5126
Publisher
American Chemical Society
Volume
137
Issue
30
Page Numbers
9694-9703
Language
English
PMID
26158198
DOI
10.1021/jacs.5b05076
Web of Science Id
WOS:000359279500033
Abstract
The development of general and more atom-economical catalytic processes for Friedel-Crafts alkylations of unactivated arenes is an important objective of interest for the production of pharmaceuticals and commodity chemicals. Ferroceniumboronic acid hexafluoroantimonate salt (1) was identified as a superior air- and moisture-tolerant catalyst for direct Friedel-Crafts alkylations of a variety of slightly activated and neutral arenes with stable and readily available primary and secondary benzylic alcohols. Compared to the use of classical metal-catalyzed alkylations with toxic benzylic halides, this methodology employs exceptionally mild conditions to provide a wide variety of unsymmetrical diarylmethanes and other 1,1-diarylalkane products in high yield with good to high regioselectivity. The optimal method, using the bench-stable ferroceniumboronic acid salt 1 in hexafluoroisopropanol as cosolvent, displays a broader scope compared to previously reported catalysts for similar Friedel-Crafts reactions of benzylic alcohols, including other boronic acids such as 2,3,4,5-tetrafluorophenylboronic acid. The efficacy of the new boronic acid catalyst was confirmed by its ability to activate primary benzylic alcohols functionalized with destabilizing electron-withdrawing groups like halides, carboxyesters, and nitro substituents. Arene benzylation was demonstrated on a gram scale at up to 1 M concentration with catalyst recovery. Mechanistic studies point toward the importance of the ionic nature of the catalyst and suggest that factors other than the Lewis acidity (pKa) of the boronic acid are at play. A SN1 mechanism is proposed where ion exchange within the initial boronate anion affords a more reactive carbocation paired with the non-nucleophilic hexafluoroantimonate counteranion.
Tags
PFAS
•
Expanded PFAS SEM (formerly PFAS 430)
Litsearch: September 2019
PubMed
Web of Science
Not prioritized for screening
2H-Perfluoro-2-propanol
•
PFAS Universe
Data Source
Pubmed
2H-Perfluoro-2-propanol
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