Thermal Isomerization of Isoborneols and Dehydroisoborneols to New Chiral Building Blocks in Terpenoid Synthesis
作者:Georg Rüedi、Hans-Jürgen Hansen
DOI:10.1002/hlca.200490179
日期:2004.8
readily prepared in excellent yields from (+)-camphor and (+)-5,6-dehydrocamphor (2) by aryl, vinyl, or alkyl Grignard addition in the presence of stoichiometric amounts of CeCl3, were thermally isomerized in a flow reactor system under DGPTI (dynamic gas-phase thermo-isomerization) conditions at temperatures between 480 and 630° to give the enantiomerically pure monocyclic carbonyl compounds 7a–7d, 19a
取代的异冰片醇1a - 1g和5,6-脱氢异冰片醇6a - 6c易于制备,可以通过(+)-樟脑和(+)-5,6-脱氢樟脑(2)的芳基,乙烯基或烷基格氏试剂的加成而制得。在流式反应器系统中,在DGPTI(动态气相热异构化)条件下,在480至630°的温度下,将化学计量的CeCl 3的存在进行热异构化,从而得到对映体纯的单环羰基化合物7a - 7d,19a, b,23和24。在所有情况下,产物的形成都在高度区域性和立体选择性方面进行。新的立体发生中心的绝对构型由1 H-NOE测量确定。提出芳基底物1a - 1d的DGPTI可以在双自由基中间状态形成后进行分子中最弱的单键的初始裂解,随后进行分子内H-抽象以提供苯乙酮衍生物7a - 7d。2 H标记研究进一步支持了该反应路径,该研究表明OH基是唯一的H源。相反,允许乙烯基基材1e和6b的DGPTI一致。Retro -ene和oxy-应对重排。在5