A NEW SYNTHETIC ROUTE TO THE TETRACYCLIC FRAMEWORK OF STRYCHNOS ALKALOIDS VIA INTRAMOLECULAR ALDOL REACTION

By treatment of ydrospiro[1H-carbazole-1,2'-[1,3]dithiolan]-4(9H)- one (1) with ethanolamine, followed by reduction of the corresponding imi ne (6) with NaBH4 to the amine (7) and benzoylation, piro-[1H-carbazol e-1,2'-(1,3)dithiolan]-4-yl}amine (8) is formed, which can be deprotec ted to yethyl)amino]-2,3,4,9-tetrahydro-1H-carbazol-1-one (9). Oxidati on of the primary hydroxyl group yields 9-tetrahydrocarbazol-1-one-4-y l)amino]acetaldehyde (10), a key-intermediate for the cyclization to 2 -benzoyl-4-hydroxy-1,2,3,4,5,7-hexahydro-1, 5c-methanoazocino[4,3-b]in dol-6-one (11), which represents the tetracyclic skeleton of Strychnos -type alkaloids.