Z. R. Valiullina, N. Ivanova, O. V. Shitikova
Oct 7, 2019
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Journal
Russian Journal of Organic Chemistry
Abstract
Methyl (Z)-3-[(2R,3R,4S,5S)-5-(2-methoxy-2-oxoethyl)-3,4-(isopropylidenedioxy)tetrahydrofuran-2-yl]-prop-2-enoate was synthesized, and its intramolecular carbocyclization was studied. This reaction proceeds smoothly and quickly under the action of t-BuOK in THF, leading to three cycles with the methoxy and methoxycarbonylmethyl side substituents trans to each other. A stepwise route for the formation of methyl (1R,2R,6S,7R,8R,9R)-9-(2-methoxy-2-oxoethyl)-4,4-dimethyl-3,5,10-trioxatricyclo[5,2,1,02,6]decane-8-carboxylate and methyl (1R,2R,6S,7R,8S,9S)-9-(2-methoxy-2-oxoethyl)-4,4-dimethyl-3.5,10-trioxatricyclo-[5,2,1,02,6]decane-8-carboxylate with the trans orientation of the side substituents is proposed. The observed stereochemical result of the reaction is interpreted in terms of epimerization in the C1 and C4 centers of methyl (Z)-3-[(2R,3R,4S,5S)-5-(2-methoxy-2-oxoethyl)-3,4-(isopropylidenedioxy)-tetrahydrofuran-2-yl]prop-2-enoate, which ultimately leads to the cyclized β,β’-cis diastereomer of methyl (Z)-3-[(2R,3R,4S,5S)-5-(2-methoxy-2-oxoethyl)-3,4-(isopropylidenedioxy)-tetrahydrofuran-2-yl]prop-2-enoate and the corresponding α,α’-cis diastereomer, a precursor of methyl (1R,2R,6S,7R,8S,9S)-9-(2-methoxy-2-oxoethyl)-4,4-dimethyl-3,5,10-trioxatricyclo[5,2,1,02,6]decane-8-carboxylate.