Efficient and library-friendly synthesis of 4-N-substituted 6-bromopyrido[2,3-d]pyrimidines under microwave irradiation

In this paper, a novel synthetic method for 4-N-substituted 6-bromopyrido[2,3-d]pyrimidines was reported. Starting from 2-aminonicotinonitrile, following by bromination of aromatic ring, condensation, cyclization, and Dimroth rearrangement, a series of 21 new pyrido[2,3-d]pyrimidine derivatives was prepared in high yields (up to 98%). In the last two steps, microwave irradiation was used. The structures of synthesized compounds were determined by NMR, IR, and HRMS techniques. The results showed that application of microwave irradiation has a beneficial effect for the preparation of desired products, as it is simple and efficient method for improving the yields and reducing the formation of undesirable by-products.