Synthesis of the potent antitumoral marine alkaloid variolin B

The synthesis of the marine alkaloid variolin B has been completed in seven steps, starting from the iminophosphorane derived from ethyl α-azido-β-(4-methoxy-7-azaindol-3-yl) acrylate, available by condensation of 2-formyl-4-methoxy-7-aza-indole with ethyl azidoacetate. Formation of the annulated 2-aminopyrimidine ring is achieved by tandem aza-Wittig/carbodiimide-mediated cyclization whereas the 2-aminopyrimidine substituent at C-5 is formed using an acetyl group as C2 moiety of the pyrimidine ring.