Biomimetic cascade cyclizations of terpenoid polyalkenes via photoinduced electron transfer. Long-distance asymmetric induction by a chiral auxiliary
Biomimetic cascade cyclizations of terpenoid polyalkenes via photoinduced electron transfer. Long-distance asymmetric induction by a chiral auxiliary
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DOI：
10.1021/ja962479u
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发表时间：
1997-02-05
影响因子：
15
通讯作者：
Demuth, M
中科院分区：
文献类型：
--
作者：
Heinemann, C;Demuth, M
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Reported herein are the first examples of highly diastereoselective cascade cyclizations of terpenoid polyalkenes Via photoinduced electron transfer (PET) 1 by means of the chiral auxiliary (-)-menthone, which is remotely located from the initiation site of the reactions. These transformations give ready access to functionalized and enantiomerically pure cyclic terpenoids.In addition to the biosynthesis of polycyclic triterpenoids Via cationic cyclizations of (3S)-2, 3-oxidosqualene, some bacteria and protozoans produce pentacyclic 3-deoxytriterpenes, such as tetrahymanol (2), Via a nonoxidative cyclization mode of squalene (1). 2 It is generally accepted that in these processes the folding of squalene in an all-prechair conformation prior to the cyclization is supported by a cyclase (Scheme 1). 2, 3 Such biosynthetic transformations have been mimicked by cationic as well as radical-type cyclizations. The former class is based on the pioneering work of Eschenmoser, Ruzicka, Jeger, and Arigoni4 and of Stork and Burgstahler5 and has been well documented in the literature. 6 Biomimetic processes triggered by radicals were first investigated by Breslow. 7 In this context we have demonstrated8 the potential of photoinduced radical cations9, 10 for triggering cascade cyclizations11 of terpenoid polyalkenes to mimic nonoxidative biosynthetic transformations. A further goal, the subject of this paper, was to efficiently induce asymmetry in such cyclizations.