Preparation of the Synthetic Equivalents of Chiral Cyclohexadienone and Cycloheptadienone: The Enantio- and Diastereo-controlled Synthesis of (-)-Clavularin B
作者:Kou Hiroya、Huilan Zhang、Kunio Ogasawara
DOI:10.1055/s-1999-2692
日期:1999.5
Both enantiomeric tricyclic enones 2 and 3 serving as the synthetic equivalents of chiral cyclohexadienone and cycloheptadienone have been prepared by lipase-mediated kinetic ester ex-change reaction as the key step. The absolute configuration of the latter has been determined by transformation of the (-)-enantiomer 3 into the known (-)-6-methyl-2-cycloheptenone 16 and the cytotoxic marine natural product (-)-clavularin B 19. However, it has been found that the seven-membered enone 3 exhibits lower diastereoselectivity and less favorable thermal stability than the five-membered and six-membered analogues.
Synthesis of optically active 6-amino-2-cycloheptenone as a convenient chiral building block for the preparation of 6-alkyl-2-cycloheptenone
作者:Masakazu Koiwa、Georges P-J. Hareau、Daisuke Morizono、Fumie Sato
DOI:10.1016/s0040-4039(99)00711-x
日期:1999.5
Opticallyactive 6-amino-2-cycloheptenone 5 has been prepared from ethyl 2(E),6-heptadienoate where the Michael addition of a chiral amine, Ti(II)-mediated intramolecular nucleophilic acyl substitution reaction and FeCl3-mediated ring expansion are the key steps. The compound 5 undergoes highly diastereoselective conjugate addition of a Grignard reagent in the presence of a catalytic amount of Li2Cu(CN)Cl2
由2(E),6-庚二烯酸乙酯制备旋光的6-氨基-2-环庚酮5,其中手性胺的迈克尔加成,Ti(II)介导的分子内亲核酰基取代反应和FeCl 3介导的扩环是关键步骤。在催化量的Li 2 Cu(CN)Cl 2存在下,化合物5经历格氏试剂的高度非对映选择性共轭加成,以提供相应的顺式加合物,其随后转化为6-烷基取代的2-通过用治疗cycloheptenones p -tsa。
A Predictable Enantioselective Total Synthesis of (+)-Clavularin A
作者:Hilmar Weinmann、Ekkehard Winterfeldt
DOI:10.1055/s-1995-4061
日期:1995.9
Cycloadduct 9 was transformed into vinylsilane 11d in a conjugate addition-alkylation sequence. Epoxidation and subsequent hydrolysis provided the clavularin adduct 14, which on flash vacuum pyrolysis (FVP) gave (+)-clavularin A (1) in 91% yield.
环加合物 9 通过共轭加成-烷基化顺序转化为乙烯基硅烷 11d。环氧化反应和随后的水解反应产生了黄烷苷加合物 14,该加合物经闪蒸真空热解(FVP)得到了 (+)-clavularin A (1),收率为 91%。