Asymmetric synthesis of octahydro-2H-pyrido[1,2-a]-pyrazines

A series of optically pure octahydro-2H-pyrido[1,2-a]pyrazines has been pre pared from (-)-2-cyano-6-phenyloxazolopiperidine (4). 2H-Pyrido[1,2-a]pyraz in-3-(4H)-one (7)and octahydro-2H-pyrido[1,2-a]pyrazine (14) were obtained from diamino alcohol (5) by cyclization of bromo- or chloroamides (6) and ( 10). (4R, 9aS)-1,1,4-Triphenyloctahydro-2H-pyrido[1,2-a]pyrazine (16) was s ynthesized by cyclization of amino alcohol (15c). The formation of cyclic u rea (8aS)-diphenyl-3-oxooctahydroimidazo[1,5-a]pyridine (18) was observed d uring the hydrogenolysis of the corresponding carbamate (17).