Stereoselective Synthesis of 2Z,4E-Configured Dienoates through Tethered Ring Closing Metathesis
作者:Bernd Schmidt、Stephan Audörsch、Oliver Kunz
DOI:10.1055/s-0035-1562536
日期:——
is described. The sequence involves Steglich esterification of the reactants, followed by a one-pot ringclosing metathesis–base induced elimination–alkylation reaction to furnish the products in high stereoselectivity. Trapping of the intermediate sodium carboxylates is accomplished efficiently using Meerwein’s salt Et3OBF4. A two-step sequence leading from racemic allylic alcohols and vinylacetic
Four diastereomers of 2-[(trimethylammonium)-methyl]-5-methyltetrahydrofuran-3-ol, trivially named isomuscarine, allo-isomuscarine, epi-isomuscarine, and epiallo-isomuscarine, were prepared as bromide salts from 2,4-like and 2,4-unlike diastereomers of 3-(4-hydroxyhex-5-en-2-oxy)-4-methylthiazole-2(3H)-thione. The strategy for constructing the tetrahydrofuran nucleus of the isomuscarines uses alkenoxyl radical 5-exo-bromocyclization, occurring 2,3-cis-selectively for the 2,4-like-4-hydroxyhex-5-en-2-oxyl radical, and 2,3-trans-selectively for the 2,4-unlike diastereomer. A fraction of 4hydroxyhex-5-en-2-oxyl radicals cyclizes 6-endo-selectively providing 5-bromo-2-methyltetrahydropyran-4-ols in yields between 3 and 15%. Substituting trimethylamine for bromide in 5-exo-bromocyclized products furnishes isomuscarine bromides, which were structurally characterized by X-ray diffraction and NMR-spectroscopy. (C) 2014 Elsevier Ltd. All rights reserved.
Markevich,V.S.; Markevich,S.M., Journal of applied chemistry of the USSR, 1968, vol. 41, # 6, p. 1323 - 1325