Treatment of 3-amino-2-methyl-1(2H)-5,6,7,8-tetrahydro-thioxoisoquinoline-4-carbonitrile(2) with formamide afforded pyrimidotetrahydroisoquinoline (3). When compound 2 was reacted with halo-compounds. N-alkylation occurred to give compounds 4-6. Also, pyrimidotetrahydroisoquinolines (8-11) were obtained when oxazinotetrahydroisoquinoline (7) was treated with aminocompounds. Furthermore, base catalysed condensation of amine with aromatic aldehydes led to expected Schiff bases.12 but additional reaction at the N-methyl group with formation of styryl compound 13 was observed when the reaction was carried out in acetic acid.