Stereoselective reactions: XIII. Total synthesis of (+)-sesbanine by a highly stereoselective cycloannelation reaction

✍ Scribed by Kiyoshi Tomioka; Kenji Koga

• Publisher: Elsevier Science
• Year: 1988
• Tongue: French
• Weight: 352 KB
• Volume: 44
• Category: Article
• ISSN: 0040-4020
• DOI: 10.1016/s0040-4020(01)86137-8

✦ Synopsis

carried out by treating 5 with 1.4-dibromobutane in dimethylformamide (DHF) in the presence of potassium tert-butoxide to afford 6 in 39% yield. Then focus was turned to the synthesis of deoxysesbanine (12). On the contrary to the easy alkoxycarbonylation of 4, treatment of 7 under the same reaction conditions with use of ethyl chloroformate lead to N-alkoxycarbonylation to afford 9.5 Fortunately, treatment of 7 with diethyl carbonate in the presence of sodium hydride in refluxing toluene afforded 8 in 53% yield. Cycloannelation of 8 under the same reaction conditions for 5 lead to the formation of 10 and 115 in 40 and 20% yields, respectively. Use of sodium hydride in place of potassium tert-butoxide improved yield to give 10 and 11 in 61 and 30% yields, respectively. The stage was thus set for the cyclic-imide formation. Selective hydrolysis of the nitrile group of 10 was carried out by utilizing alkaline temperature to give directly deoxysesbanine (12) in CN r COeEt N CN 8 hydrogen peroxide in aqueous ethanol6 at room 83% yield.