Allenes. Part 47. Pyrido[1,2-a]pyrimidines and their hydrolysis products from allenic and acetylenic nitriles

Abstract

The reactions between 2-aminopyridine, C-substituted 2-aminopyridines, and allenic nitriles or phenylpropynenitrile give, initially, 2-amino-2H-pyrido[1,2-a]pyrimidines which are moderately stable under acidic conditions but undergo addition of water with extreme ease under basic conditions to form 4-hydroxypyrido[1,2-a]pyrimidines. These undergo ring cleavage when refluxed in ethanol to pyridyl ketones (5).