Synthesis of (±)-Bakkenolide-A and Its C-7, C-10, and C-7,10 Epimers by Means of an Intramolecular Diels−Alder Reaction
作者:Thomas G. Back、Victor O. Nava-Salgado、Joseph E. Payne
DOI:10.1021/jo015624h
日期:2001.6.1
cases exo cyclization was preferred over endo. An alternative approach was based on a similar intramolecular Diels-Alder cycloaddition, using dimethyl malonate instead of ethyl 4-benzyloxyacetoacetate as the starting material for the double alkylation preceding the cycloaddition step. The cycloadduct was then converted into the corresponding alpha-phenylseleno propargyl esters 16 or 22. However, attempted
(+/-)-bakkenolide-A(1)由4-苄氧基乙酰乙酸乙酯通过依次与tiglyl溴化物和(Z)-5-bromo-1,3-pentadiene依次烷基化,然后用分子内Diels-Alder烷基化制备,从五个步骤制备(+/-)- (E,Z)-三烯25b的反应是关键步骤。将该氢化丙烷环加合物28进行氢化和自发或酸催化的内酯化,然后进行维蒂希反应以引入1的环外亚甲基。已知的7-表环烯酮-A(2)和新颖的10-表环-和7,10获得了作为小副产物的-diepibakkenolide-A(分别为3和4)立体异构体。当使用(E)-5-溴-1,3-戊二烯代替Z-异构体时,主要的产物是10-表-和7,10-二哌酮。在这两种情况下,外环化均优于内环化。另一种方法是基于类似的分子内Diels-Alder环加成反应,使用丙二酸二甲酯代替4-苄氧基乙酰乙酸乙酯作为环加成步骤之前进行双烷基化的原料。然后将环加