Total Synthesis of 7′-Desmethylkealiiquinone, 4′-Desmethoxykealiiquinone, and 2-Deoxykealiiquinone
作者:Heather M. Lima、Rasapalli Sivappa、Muhammed Yousufuddin、Carl J. Lovely
DOI:10.1021/jo4027337
日期:2014.3.21
Synthetic approaches to the imidazonaphthoquinone core of kealiiquinone and related Leucetta-derived alkaloids are described. The polysubstituted benzimidazole framework can be constructed through intramolecular Diels-Alder reactions of propiolate-derived enynes followed by oxidation. Adjustment of the oxidation state of the thus formed lactone allows introduction of the 2,3-dihydroxybenzoquinone moiety through a presumed benzoin-like condensation between a phthaldehyde derivative and a masked glyoxal equivalent catalyzed by a cyanide ion. Oxidation of the C2-position can be accomplished through application of an operationally simple treatment of an imidazolium salt with bleach, thus producing the corresponding 2-imidazolone. Debenzylation of a late stage intermediate en route to kealiiquinone was compromised by concomitant O-demethylation upon treatment with triflic acid resulting in the formation of non-natural 7'-desmethylkealiiquinone. Other endgame strategies were evaluated; however, these efforts did not lead to completion of a synthesis of kealiiquinone but did provide access to other closely related analogues.
Intramolecular Diels–Alder chemistry of 4-vinylimidazoles
作者:Yong He、Pasupathy Krishnamoorthy、Heather M. Lima、Yingzhong Chen、Haiyan Wu、Rasapalli Sivappa、H. V. Rasika Dias、Carl J. Lovely
DOI:10.1039/c0ob00657b
日期:——
An investigation of 4-vinylimidazoles as diene components in the intramolecularDiels–Alder reaction is described. In the course of these studies several parameters affecting the cycloaddition were evaluated including the nature of the imidazole protecting group, the type of dienophile and the linking group. These investigations established that amino linkers were generally more effective than either