Lewis acid-directed cyclocondensation of piperidone enol ethers with 2-methoxy-4-(N-phenylsulfonyl)-1,4-benzoquinoneimine: A new regioselective synthesis of oxygenated carbolines

Lewis acid-directed cyclocondensations of piperidone enol ethers with 2-met hoxy-4-(N-phenylsulfonyl)-1,4-benzoquinoneimine are reported. Benzofurans a re obtained with BF3. OEt2 as a promoter, whereas use of excess amounts of TiCl4:Ti(OiPr)(4) leads to tetrahydrocarbolines. The latter reactions provi de expedient routes to oxygen-substituted tetrahydrocarbolines and carbolin es. As applications of this new methodology, the preparations of 1-[3-(dime thylamino)propyl] amino-7-methoxy- and 1-[3-(dimethylamino)propyl]amino-7,8 -dimethoxy-5H-pyrido[4,3-b]indoles are described.