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2,6‐Disubstituted 4‐Aminopyridines from 1,3‐Dialkoxy‐2‐azapropenylium Salts and N ‐Methyl‐4‐piperidone Enamines
Author(s) -
Schleimer Richard,
Würthwein ErnstUlrich
Publication year - 1994
Publication title -
chemische berichte
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 0009-2940
DOI - 10.1002/cber.19941270817
Subject(s) - chemistry , bicyclic molecule , iminium , hydrolysis , medicinal chemistry , yield (engineering) , organic chemistry , ketone , catalysis , materials science , metallurgy
1,3‐Dialkoxy‐2‐azapropenylium salts 1 react with enamines 2 of N ‐methyl‐4‐piperidone at room temperature to give 2,6‐disubstituted 4‐aminopyridines 4 , 5 in low to moderate yield after hydrolysis. Intermediates of the reaction of 1a with 2 are the bicyclic iminium salts 6 and 7 , which may be detected 1 H‐NMR spectroscopically prior to hydrolysis. Hydrolysis of the mixture obtained from the reaction of 1a with 2a under basic conditions furnishes the bicyclic ketone 3 as the major product. A “retro‐Mannich”‐type reaction is suggested to explain the degradation of the bicyclic intermediates 6 , 7 with the formation of the pyridines 4 , 5 .