A new, one-pot, three-component synthesis of 4H-pyrido[1,2-a]-pyrimidines, 4H-pyrimido[1,2-a]pyrimidines, and 4H-pyrazino[ 1,2-a] pyrimidines

A new, one-pot and three-component synthesis of 4H-pyrido[1,2-a]pyrimidines, 4H-pyrimido[1,2-a]pyrimidines, and 4H-pyrazino[1,2-a]pyrimidines is described. The reactive 1:1 zwitterionic intermediate, formed by the addition of isocyanides to dialkyl acetylene-dicarboxylates, was trapped by N-(2-heteroaryl)amides to yield a ketenimine intermediate, which was cyclized and then rearranged under the reaction conditions to afford the title compounds under mild reaction conditions in good yields. Single-crystal X-ray analysis conclusively confirms the structure of the obtained bridgehead bicyclic 6-6 heterocyclic compounds. (c) 2007 Elsevier Ltd. All rights reserved.