Developing the work done [I-3] on synthesizing new pyrido [2, 3-d] pyrimidine derivatives in order to find biologically active substances, we have studied the reaction of 1, 3-dimethy•-2, 4, 5-tri• x•-6-nitr•-7-ch•• r•-•, 2, 3, 4, 5, 8-hexahydr• pyrid•[2, 3-d] pyrimidine(I)[i] with aliphatic