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1‐Acyl‐4‐benzylpyridinium Tetrafluoroborates: Stability, Structural Properties, and Utilization for the Synthesis of Acyl Fluorides
Author(s) -
Wagner Rüdiger,
Wiedel Bernd,
Günther Wolfgang,
Görls Helmar,
Anders Ernst
Publication year - 1999
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/(sici)1099-0690(199909)1999:9<2383::aid-ejoc2383>3.0.co;2-t
Subject(s) - chemistry , thermal instability , moiety , lewis acids and bases , inert , ab initio , carboxylic acid , pyridine , ab initio quantum chemistry methods , thermal stability , acylation , computational chemistry , combinatorial chemistry , organic chemistry , molecule , catalysis , physics , mechanics
1‐Acyl‐4‐benzylpyridinium salts 4 containing nonnucleophilic anions X – such as CF 3 SO 3 – , FSO 3 – , and BF 4 – can be generated quantitatively and in situ from 1‐acyl‐4‐alkylidene‐1,4‐dihydropyridines 1a – f and the corresponding acid, HX. The BF 4 – salts reveal an interesting and unexpected thermal instability which allows the convenient synthesis of carboxylic acid fluorides 5b – f . This procedure offers advantages over known methods: All operations can be performed in a standard glass apparatus and do not require high pressures. The formation of RCOF 5 is assisted by the pyridine moiety of 4 , which splits off and functions as a Lewis base to intercept the BF 3 acid. The structural and electronic relationships as well as dominating differences between the very reactive cations of 4 and their almost “inert” uncharged precursors, the dihydropyridines 1 , are discussed both on the fundament of experimental evidence (X‐ray structures of 1f and the extremely reactive and very labile 4f ) and theoretical investigations (ab initio and DFT MO calculations).