Journal of Organic Chemistry p. 3209 - 3214 (1981)
Update date:2022-08-02
Topics:
Rastetter, William H.
Phillion, Dennis P.
Thiol-functionalized crown ethers serve as reagents for macrolide closures.The thioesters derived from these crown ethers and ω-hydroxy carboxylic acids yield macrolides when treated with potassium tert-butoxide.The cyclization reaction proceeds via a templated conformation in which the ω-alkoxide is held proximate to the thioester through ionic bonding to the crown-bound potassium cation.Variations in crown ether structure in the series 1-4 show that the criterion of proximate binding is necessary but not sufficient to ensure efficient macrolide closure.The optimal crown ether reagent is thought to provide transition-state stabilization for the attack of the alkoxide on the thioester carbonyl by situating the carbonyl oxygen immediately adjacent to the crown-bound potassium cation.
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