ISSN:
0018-019X
Keywords:
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The base-catalyzed intramolecular cyclization of polycyclic olefinic alcohols of type a (10-endo-hydroxy-anti9,10-tricyclo [4.2.1.12,5]dec-7-en-9-ones (type h), anti9,10-tricyclo[4.2.1.12,5] dec-3-en-9-endo-ols (type j), and anti10,11-tricyclo[4.3.1.12,5]undec-3-en-10-endo-ols (type 1)) to the ethers d and f, resp., has been studied. A mechanism for the nucleophilic addition of the corresponding alkoxide anion b to the isolated C,C—double bond is discussed. It is proposed that b is formed (fast acid/base equilibrium) in the first step. For the subsequent reaction sequence, there are two well distinguishable pathways: (a) Compounds with an additional carbonyl group (h) cyclize via a homoenolate-like intermediate c, which is protonated stereoselectively on the exo-side by the hydroxylic solvent. (b) Compounds without a carbonyl group (j and l) cyclize 102-104 times slower, and the reaction proceeds via a carbanion-like transition state e. The proton transfer from the hydroxylic solvent is clearly coupled with the C,O—bond formation. Steric compression in the olefinic alcohols a influences the cyclization rate: (a) Alcohols with a smaller ring (h, X = CH2CH2) cyclize 70-200 times faster than the ones with a larger ring (1, X = CH2CH2CH2). (b) Replacement of the H-atom at the carbinol C-atom by a CH3 group enhances the rate of ether formation by a factor of 50-100. Due to through-bond interactions between the C,C-double bonds, olefinic alcohols with an additional endocyclic C,C-double bond (h and j, X = CH=CH) cyclize 20-300 times faster than the corresponding monoolefinic ones (h and j, X = CH2CH2).
Additional Material:
2 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/hlca.19850680817
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