<i>endo</i>/<i>exo</i>Stereoselectivity in<i>Diels</i><i>Alder</i>Reactions of<i>α</i>,<i>β</i>-Dialkylated Conjugated Enals to Cyclic 1,3-Dienes: Intermediates in the Synthesis of (−)-<i>β</i>-Santalol and Its Analogs
作者:Christian Chapuis、David Skuy、Jean-Yves de Saint Laumer、Robert Brauchli
DOI:10.1002/cbdv.201400060
日期:2014.10
to α,β-dialkyl conjugated enals 5 are compared with the analogous endo-favored Diels-Alder reaction of cyclohexa-1,3-diene 7. The exo-stereoselectivity is lower in the homologous case of methylcyclopenta-1,3-diene 9. This diastereoselectivity is discussed either in terms of a retro-homo-Diels-Alder reaction, associated with thermodynamic control, or with respect to either a competing hetero-Diels-Alder/Claisen
将环戊-1,3-二烯2a与α,β-二烷基共轭烯5的高度外选[4 + 2]环加成反应与环己-1,3-二烯7的类似内生的Diels-Alder反应进行了比较。在甲基环戊-1,3-二烯9的同源情况下,外立体选择性较低。该非对映选择性是通过逆热Diels-Alder反应(与热力学控制相关)来讨论的,或者是关于竞争性的杂合的Diels-Alder / Claisen或Cope多米诺途径,或内同环加合物的Retro-Claisen / retro-hetero-Diels-Alder。这些假设机制已通过DFT计算在AlCl3介导的5d至2a和7的AlCl3介导的环加成反应的理论水平上通过MPT1K(CH2 Cl2)/ 6-31 + G **进行了检验。