A SIMPLE STEREOSELECTIVE VERSION OF CLAISEN REARRANGEMENT LEADING TO TRANS-TRISUBSTITUTED OLEFINIC BONDS . SYNTHESIS OF SQUALENE
A SIMPLE STEREOSELECTIVE VERSION OF CLAISEN REARRANGEMENT LEADING TO TRANS-TRISUBSTITUTED OLEFINIC BONDS . SYNTHESIS OF SQUALENE
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DOI：
10.1021/ja00706a074
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发表时间：
1970-01-01
影响因子：
15
通讯作者：
PETERSEN, MR
中科院分区：
文献类型：
--
作者：
JOHNSON, WS;WERTHEMANN, L;PETERSEN, MR
我们希望公开一种具有高度立体选择性的Claisen重排反应，该反应可用于合成TZ-azzy-三取代烯键。该方法简单地将烯丙醇1与过量的原乙酸乙酯一起加热，并存在微量的弱酸(如丙酸)。与经典的乙烯基醚裂解反应(以H代替ETO)相比，该方法操作简单(一步操作，而不是两步操作)，且总收率和立体选择性较高。这种高的立体选择性可能是由于乙氧基和R2基团(3)之间的非成键相互作用所致，这些相互作用只在过渡状态下发展，从而导致顺式产物。2.
We wish to disclose a version of the Claisen rearrange-ment which is highly stereoselective and can be applied to the synthesis of tz-azzy-trisubstituted olefinic bonds. The method simply involves heating an allylic alcohol, 1, with excess ethyl orthoacetate in thepresence of a trace of weak (eg, propionic) acid. Evidently a mixed orthoester, 2, is first formed and loses ethanol to form the ketene acetal 3 which rearrangesto the olefinic ester 4.1As compared with the classical pyrolysis of simple vinyl ethers (3 with H in place of EtO), this orthoester process is simpler to perform (one instead of two opera-tions), and the overall yield as well as stereoselectivity is higher. The high stereoselectivity is probably attribu-table to nonbonded interactions between the ethoxy and R2 groups (3) that develop only in the transition state leading to cis product. 2