The oxyanion derived from hydroxyacrylate E-(5)
undergoes smooth intramolecular Michael addition to give the
trans-2,6-disubstituted tetrahydropyran (7) as the major
product of reaction. In contrast, the oxyanion obtained from isomer
Z-(5) cyclizes to give the
cis-2,6-disubstituted tetrahydropyran (6) as the major
product. Such chemistry has been extended to the enantioselective synthesis of
(+)-(6) the acquisition of which constitutes a formal total synthesis of
acid (+)-(2), a constituent of the glandular secretion from the civet cat
(Viverra civetta). Reductive amination of keto acrylate
(12) affords an intermediate amine which cyclizes,
in situ, to give the
cis-2,6-disubstituted piperidine (26). Analogous
treatment of compound (13) delivers the isomeric
trans-2,6-disubstituted piperidine (27) as the exclusive
product of reaction. Transition state structures have been proposed to account
for the diastereoselectivities observed in all of the cyclization reactions.
羟基丙烯酸酯 E-(5)的氧阴离子
发生顺畅的分子内迈克尔加成反应,得到反式-2,6-二取代的四氢吡喃(7
反式-2,6-二取代的四氢吡喃(7)作为主要反应产物。
反应的主要产物。相反,从异构体
Z-(5) 环化生成
顺式-2,6-二取代的四氢吡喃(6)为主要反应产物。
产品。这种化学反应已经扩展到对映体选择性合成
(+)-(6) 的对映体选择性合成。
酸 (+)-(2) 的正式全合成。
(Viverra civetta)腺分泌物的一种成分。酮基丙烯酸酯的还原胺化反应
(12) 发生还原胺化反应,生成中间胺,并在原位环化、
在原位环化,生成
顺式-2,6-二取代哌啶 (26)。类似的
处理化合物 (13) 得到异构体
反式-2,6-二取代哌啶(27)作为唯一的
反应产物。有人提出了过渡态结构来解释
在所有环化反应中观察到的非对映选择性。