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Indolizine derivatives. VII. indolizines via cyclizations of 2‐(2‐Pyridyl)methylene‐1,3‐diketones and −1,3‐Keto esters
Author(s) -
Pohjala Esko K.
Publication year - 1977
Publication title -
journal of heterocyclic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.321
H-Index - 59
eISSN - 1943-5193
pISSN - 0022-152X
DOI - 10.1002/jhet.5570140223
Subject(s) - chemistry , methylene , acetic anhydride , indolizine , yield (engineering) , medicinal chemistry , cycloaddition , bicyclic molecule , organic chemistry , diketone , catalysis , materials science , metallurgy
The reaction of 3‐(2‐pyridyl)methylene‐2,4‐pentanedione with acetic anhydride gives at 60° 1‐(1‐acetoxy‐3‐methyl‐2‐indolizinyl)ethanone ( 3a ) or, in the presence of 2,4‐pentanedione, 3‐(2‐acetyl‐3‐methyl‐7‐indolizinyI)‐2,4‐pentanedione ( 7a ) in good yield. In refluxing acetic anhydride, 1‐(3‐methyl‐2‐indolizinyl)ethanone ( 4a ) is the main product. In refluxing dimethyl sulfoxide the cycloaddition product, 3‐[2‐acetyl‐3‐(2‐pyridyl)‐l‐indolizinyl)]‐2,4‐pentanedione ( 6 ), is obtained. Ethyl 2‐(2‐pyridyl)methylene‐3‐oxobutanoate and ethyl 2‐(2‐pyridyl)methylene‐3‐oxo‐3‐phenylpropanoate behave analogously. The stereochemistry of the keto esters has a marked influence on the course of cyclization. The mechanisms are discussed.