67998-48-5Relevant academic research and scientific papers
N-acylpyridinium trifluoromethanesulfonates and tetrafluoroborates: Shuttle reagents for the acylation of enantiopure secondary alcohols
Wagner, Rüdiger,Günther, Wolfgang,Anders, Ernst
, p. 883 - 888 (2007/10/03)
Several enanflopure alcohols are esterified with N-acyl-4- benzylpyfidinium trifluoromethanesulfonates 7b,d,f or tetrafluoroborates 7a,c,e. These reagents, which can be generated in situ, or isolated as stable salts, are synthesized from readily available 4-alkylpyridines 3, acyl chlorides 4 and strong protic acids 6. The acyl moiety is transferred under neutral conditions and in high yields. The heterocyclic component 3a can be re-isolated almost quantitatively. The acetate, benzoate and pivaloate groups were selected with regard to their application as frequently used protecting groups for hydroxy compounds. As shown by paramagnetic shift experiments with a chiral europium(III) complex, these acylations proceed without detectable racemization or epimerization.
Acylation Reactions of Carbonyl Compounds with 1-Acylpyridinium Salts
Anders, Ernst,Will, Wolfgang,Gassner, Thomas
, p. 1506 - 1519 (2007/10/02)
1-Acyl-4-benzylpyridinium tetrafluoroborates 5 have been used to derive generally applicable guidelines for the reaction of aldehydes 6 and ketones 7 with 1-acylpyridinium salts (scheme 2): a) Non-enolizable aldehydes 6 react with 5 to give N-pyridinium salts 14. b) Enolizable aldehydes 6 can be transformed by means of 5 into pyridinium salts 14 and enol esters 12, respectively.Using aldehyde 6b as an example, it was possible to show that the reaction course (formation of 12 or 14) can be controlled by simple variation of the reaction conditions. c) In general, ketones will not react with 5.The range of applicability of this guidelines has been defined. - We suggest, that the reaction course is mainly determined by the formation of the carbenium ion 19 and the aldehyde-pyridine derivative addition product 8.
1-Acyl-4-alkylidene-1,4-dihydropyridines, 7. Activation with Boron Trifluoride: Intermolecular Acyl Group Transfer and Formation of 1-(4-Pyridyl)-2-alkanones
Anders, Ernst,Will, Wolfgang,Stankowiak, Achim
, p. 3192 - 3204 (2007/10/02)
1-Acyl-4-alkylidene-1,4-dihydropyridines 5, representatives of the thermally stable enamides, can be activated by means of boron trifluoride 6, so the ketones 7 result from attack of 6 on 5 (intermolecular acyl group transfer).The mechanism of this reaction, which has not previously been observed for enamides, is strongly suggested to be as follows: 5 and 6 form first the adduct 21, which attacks 5 with formation of 27.Special examples of 5 (11 and 12) are found to be reactive enough that the ketone 7h or the sulfone 15 can be obtained from their isolable precursors (14 and 13) without Lewis-acid activation. 13 is particularly noteworthy: being the precursor of the salt 16, which is generated in situ, it serves as an extremely effective tosylating agent.Even tertiary alcohols are attackted by 16.
