Abstract
Octahydropyrido [1, 2-a] pyrazine (VI) and its N-benzyl derivative (I) were subjected to oxidation by mercuric acetate to afford 1, 3, 4, 6, 7, 8-hexahydro-2H-pyrido [1, 2-a] pyrazin-1-one (VII) and its N-benzyl compound (II), respectively. The former product (VII) was also obtained by similar oxidation of the lactam (V). Compound (V) was treated with methyl iodide in methanol to give two isomeric methiodides, trans-octahydropyrido [1, 2-a]-pyrazin-1-one methiodide (Xa) and the corresponding cis-methiodide (Xb). On thermal treatment, the latter methiodide was converted into the former. Methiodides, IV, XI, Xa, and Xb were reduced with lithium-liquid ammonia giving the 10-membered ring lactam (XII) in 4%, 52%, 81%, and 82% yields, respectively. When treated with sodium amalgam, Xa gave XII in 59% yield, which, on reduction with lithium aluminum hydride, yielded XIII.
