72551-50-9Relevant articles and documents
Asymmetric Hydrogenation of 3-Substituted Pyridinium Salts
Renom-Carrasco, Marc,Gajewski, Piotr,Pignataro, Luca,de Vries, Johannes G.,Piarulli, Umberto,Gennari, Cesare,Lefort, Laurent
supporting information, p. 9528 - 9532 (2016/07/14)
The use of an equivalent amount of an organic base leads to high enantiomeric excess in the asymmetric hydrogenation of N-benzylated 3-substituted pyridinium salts into the corresponding piperidines. Indeed, in the presence of Et3N, a Rh-JosiPhos catalyst reduced a range of pyridinium salts with ee values up to 90 %. The role of the base was elucidated with a mechanistic study involving the isolation of the various reaction intermediates and isotopic labeling experiments. Additionally, this study provided some evidence for an enantiodetermining step involving a dihydropyridine intermediate.
Reductive alkylation of pyridinium salts. Part 1. Synthesis of di-, tetra- and hexa-hydropyridine esters
MacTavish, Kohn,Proctor, George R.,Redpath, James
, p. 2545 - 2552 (2007/10/03)
Reaction of 1-methyl-, 1-benzyl- and 1-benzoyl-4-ethoxycarbonylpyridinium salts 1 with zinc and benzyl bromide produce regioselectively the 4,4-disubstituted 1,4-dihydropyridines 3 (R = CH3, PhCH2, PhCO); only the latter is stable but all are reduced catalytically to piperidines 2 (R = CH3, PhCH2, PhCO). 1-Benzoyl-4-ethoxycarbonylpyridinium chloride with zinc and benzoyl chloride or ethyl bromoacetate gives respectively 4-benzoyl- 18 or 4-ethoxycarbonylmethyl-1-benzoyl-4-ethoxycarbonyl-1,4-dihydropyridine 17, but 1-methyl-4-ethoxycarbonylpyridinium iodide 1 (R = CH3, X = I) with benzoyl chloride gives 3-benzoyl-4-ethoxycarbonyl-1-methyl-1,2-dihydropyridine 21.The action of zinc and benzyl bromide on 1-methyl- and 1-benzyl-3-ethoxycarbonylpyridinium salts 5 gives, after catalytic hydrogenation, mixtures of 2- and 4-benzyl-5-ethoxycarbonyl-1,2,3,4-tetrahydropyridines 6 and 7 (R = CH3 or PhCH2) but similar treatment of 1-benzoyl-3-ethoxycarbonylpyridinium chloride 5 (R = PhCO, X = Cl) yields selectively the stable 4-benzyl-3-ethoxycarbonyl-1,4-dihydropyridine 9.Treatment of 1-methyl- or 1-benzoyl-3-ethoxycarbonylpyridinium salts 5 with zinc and benzoyl chloride gives a mixture of products. 1-Methyl-2-ethoxycarbonylpyridinium iodide 11 (R = CH3, X = I) reacts with zinc and benzyl bromide giving, after catalytic hydrogenation, 2-, 4- and 6-benzyl-2-ethoxycarbonyl-1-methylpiperidines 12, 13 and 14 (R = CH3) in the ratio 2:7:1, but 1-benzyl-2-ethoxycarbonylpyridinium bromide 11 (R = PhCH2, X = Br) gives only 1,4-dibenzyl-2-ethoxycarbonylpiperidine 13 (R = PhCH2).
