An Effective Method for the Preparation of Chiral Polyoxy 8-Membered Ring Enone Corresponding to the B Ring of Taxol
作者:Isamu Shiina、Jun Shibata、Ryoutarou Ibuka、Yumiko Imai,、Teruaki Mukaiyama
DOI:10.1246/bcsj.74.113
日期:2001.1
An effective method for the preparation of 8-membered ring enone, (4S,5R,7R,8R)-4,8-bis(benzyloxy)-7-(t-butyldimethylsiloxy)-5-(4-methoxybenzyloxy)-2,6,6-trimethylcyclooct-2-enone (1), in sufficient quantities was developed. Optically active trioxy aldehyde, (3R,4S)-4-benzyloxy-5-(t-butyldimethylsiloxy)-3-(4-methoxybenzyloxy)-2,2-dimethylpentanal (3), was prepared first by diastereoselective dihydroxylation of (2R,4S)-2-(4-methoxyphenyl)-5,5-dimethyl-4-vinyl-1,3-dioxane derived from D-pantolactone. Next, 8-chloro-7-oxoaldehyde, (2R,3R,5R,6R)-2,6-bis(benzyloxy)-5-(t-butyldimethylsiloxy)-8-chloro-3-(4-methoxybenzyloxy)-4,4-dimethyl-7-oxononanal (30), was newly synthesized by the following reactions: i) MgBr2•OEt2-mediated diastereoselective aldol reaction of the aldehyde 3 with (Z)-2-benzyloxy-1-methoxy-1-(trimethylsiloxy)ethene and ii) reaction of methyl (2R,3R,5R,6S)-2,6-bis(benzyloxy)-3,7-bis(t-butyldimethylsiloxy)-5-(4-methoxybenzyloxy)-4,4-dimethylheptanoate with 1,1-dichloroethyllithium, followed by successive reductive dehalogenation of thus formed 1,1-dichloroethyl ketone with 1,1-dichloroethyllithium. Then, the chiral 8-chloro-7-oxoaldehyde 30 was converted to the 8-membered ring enone 1 by SmI2-mediated aldol cyclization.
开发了一种有效制备八元环烯酮(4S,5R,7R,8R)-4,8-二(苄氧基)-7-(叔丁基二甲基硅氧基)-5-(4-甲氧基苄氧基)-2,6,6-三甲基环辛-2-烯酮(1)的方法,可获得足量产物。首先,通过对(2R,4S)-2-(4-甲氧基苯基)-5,5-二甲基-4-乙烯基-1,3-二氧六环进行非对映选择性二羟基化反应,制备了光学活性三氧基醛(3R,4S)-4-苄氧基-5-(叔丁基二甲基硅氧基)-3-(4-甲氧基苄氧基)-2,2-二甲基戊醛(3),该化合物源自D-乳酸内酯。随后,通过以下反应新合成了8-氯-7-氧代醛(2R,3R,5R,6R)-2,6-二(苄氧基)-5-(叔丁基二甲基硅氧基)-8-氯-3-(4-甲氧基苄氧基)-4,4-二甲基-7-氧代壬醛(30):i)镁溴化物•OEt2介导的醛3与(Z)-2-苄氧基-1-甲氧基-1-(三甲基硅氧基)乙烯的非对映选择性羟醛反应,以及ii)甲基(2R,3R,5R,6S)-2,6-二(苄氧基)-3,7-二(叔丁基二甲基硅氧基)-5-(4-甲氧基苄氧基)-4,4-二甲基庚酸酯与1,1-二氯乙基锂的反应,接着通过1,1-二氯乙基锂连续还原脱卤,生成1,1-二氯乙基酮。最后,通过SmI2介导的羟醛环化反应,将手性的8-氯-7-氧代醛30转化为八元环烯酮1。