An expeditious synthesis of (+/-)-decahydro-5H-dipyrrolo[1,2-a : 1 ',2 '-c]pyrimidine-5-carbonitrile: a formal synthesis of (+/-)-tetraponerines-1, -2, -5, and -6

A short and practical synthesis of (+/-)-decahydro-5H-dipyrrolo[1,2-a:1',2' -c]pyrimidine-5-carbonitrile (17), a pivotal intermediate in the synthesis of (+/-)-tetraponerines-1 (5), -2 (6), -5 (7), and -6 (8), in three steps a nd 24% overall yield, from simple and inexpensive starting materials, is re ported. The key step of our synthesis is a one pot stereoselective multiste p process, whereupon two molecules of Delta(1)-pyrroline (9) react with die thyl malonate (10) to afford the tricyclic lactam ester 13, possessing the tetraponerine skeleton. Hydrolysis of the carboethoxy group of 13 followed by decarboxylation yields lactam 15, which is converted into alpha-aminonit rile 17. Our fruitless efforts to transform lactam 15 into the tetraponerin es through reductive alkylation are also discussed.