Intra- and intermolecular hetero-Diels-Alder reactions. 34. Enantioselective total synthesis of the mycotoxin (-)-talaromycin B by a hetero Diels-Alder reaction
作者:Lutz F. Tietze、Christoph Schneider
DOI:10.1021/jo00007a040
日期:1991.3
(-)-Talaromycin B was formed in an overall yield of 5% in nine steps via a hetero Diels-Alder reaction of the exocyclic vinyl ether 3 and methyl O-benzoyldiformylacetate (4) as the key transformation. The enantiomerically pure vinyl ether 3 was prepared in 28% yield and ee > 98% by alkylation of the N-butyryloxazolidinone 5 with 1-bromo-4-(trimethylsilyl)-2butyne (6), followed by a reduction-hydrogenation-protodesilylation sequence to give 9, which was transformed into 3 by iodoetherification with iodine and elimination with DBU. Methyl O-benzoyldiformylacetate (4) was synthesized by formylation of methyl 3,3-dimethoxypropionate, followed by benzoylation. The cycloaddition of 3 and 4 gave predominantly the desired adduct 11 together with the other three possible diastereomers. (-)-Talaromycin B (2) was obtained from 11 by reduction with DIBAL-H and stereoselective hydrogenation with platinum as catalyst. For purification purposes, 2 was transformed into a cyclic silyl ether by reaction with 1,3-dichloro-1,1,3,3-tetraisopropyldisiloxane.
(-)-塔拉霉素B通过一个包含9步反应的合成路线制得,总产率为5%。其中关键的一步是将外环乙烯基醚3与甲基邻苯甲酰二甲酰醋酸酯4通过异氧戴斯-阿尔德反应生成。对映体纯的乙烯基醚3由N-丁酰氧杂二环酮5与1-溴-4-(三甲基硅基)-2-丁炔6的烷基化反应制得,产率为28%,ee值大于98%。随后经过还原、氢化及脱硅基等一系列反应得到9,再通过与碘的醚化反应及DBU引发的消除反应得到3。甲基邻苯甲酰二甲酰醋酸酯4由甲基3,3-二甲氧基丙酸酯经过甲酰化和苯甲酰化反应制得。3和4的环加成反应主要生成目标加成物11,同时也伴随其他三种可能的非对映异构体。(-)-塔拉霉素B(2)由11经DIBAL-H还原及Pt催化下的立体选择性氢化反应制得。为了便于纯化,2与1,3-二氯-1,1,3,3-四异丙基二硅氧烷反应转化为环状硅醚。