Stereoselective synthesis of (±)-veadeiroic acid and (±)-veadeirol by cyclisation of a 2-(2-arylethyl)-1,3,3-trimethylcyclohexyl cation: mechanism and stereochemistry of related cycloalkylation reactions

Saha, Arabinda ; Nasipuri, Dhanonjoy (1993) Stereoselective synthesis of (±)-veadeiroic acid and (±)-veadeirol by cyclisation of a 2-(2-arylethyl)-1,3,3-trimethylcyclohexyl cation: mechanism and stereochemistry of related cycloalkylation reactions Journal of the Chemical Society, Perkin Transactions 1 (18). pp. 2223-2228. ISSN 0300-922X

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Official URL: http://pubs.rsc.org/en/Content/ArticleLanding/1993...

Related URL: http://dx.doi.org/10.1039/P19930002223

Abstract

(±)-Veadeiroic acid 1 and (±)-veadeirol 2, two new cleistanthoid diterpenes, have been synthesized by stereoselective cyclisation of the carbocation 5 generated from the cyclohexanol 26. The latter is prepared from 2-ethyl-3-formylbenzoic acid (with CO2H masked as an oxazoline ring) by successive reaction with 3-methylbutan-2-one, Robinson annutation, and reduction of the styrylcyclohexenone 24. The stereochemistry of cycloalkylation of the carbocations A, which ranges from 100%trans to 50 : 50 cis-trans ring-fusion as a non-activated aryl ring becomes activated by substitution, has been rationalised on the basis of the shift of the rate-determining step from the formation of s-complexes to that of π-complexes and the steric interactions therein.

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