569-10-8Relevant articles and documents
Highly selective three-step synthesis of rhein in chloroaluminate molten salt: preclusion of the Hayashi rearrangement
Gonnot, Vanessa,Antheaume, Cyril,Nicolas, Marc,Mioskowski, Charles,Baati, Rachid
experimental part, p. 6205 - 6210 (2010/03/24)
An expeditious, three-step synthesis of rhein (2) was optimized starting from bis(N, N-diethyl)-5-methoxybenzene-1,3-dicarboxamide. The key final step, involving deprotection/cyclization of orihobenzoylbenzoic acid 9 in acidic chloroaluminate molten salts
Asymmetric Diels-Alder Reactions. Part 6. Regio- and Stereo-selective Cycloadditions of 5-(2',3',4',6'-Tetra-O-acetyl-β-D-glucopyranosyloxy)-1,4-naphthoquinone
Beagley, Brian,Curtis, Anthony D. M.,Pritchard, Robin G.,Stoodley, Richard J.
, p. 1981 - 1991 (2007/10/02)
The title naphthoquinone 1d underwent reaction with cyclopentadiene to give a cycloadduct, established as (1R,4S,4aR,9aS)-1,4,4a,9a-tetrahydro-5-(2',3',4',6'-tetra-O-acetyl-β-D-glucopyranosyloxy)-1,4-methano-9,10-anthraquinone 9a by X-ray crystallographic analysis.Single cycloadducts, assigned the structures 4d, 4e and 17 were also isolated from the reactions of the naphthoquinone 1d with (E)-1-methoxy-3-trimethylsiloxybuta-1,3-diene 2b, (E)-3-methyl-1-trimethylsiloxybuta-1,3-diene 2f and (E)-2-methyl-1-trimethylsiloxybuta-1,3-diene 16.A 2:1 mixture of cycloadducts, formulated as the regioisomers 4g and 3f, arose in the reaction of the dienophile 1d with (E)-1-acetoxy-3-methylbuta-1,3-diene 2g. The sugar auxiliary was readily detached from the oxidation product of compound 9a, i.e. (1R,4S)-1,4-dihydro-5-(2',3',4',6'-tetra-O-acetyl-β-D-glucopyranosyloxy)-1,4-methano-9,10-anthraquinone 18b, by acidic hydrolysis to give the aglycone 18a. An X-ray crystallographic analysis of compound 1d revealed that the quinone ring adopts a boat-like geometry in which the carbonyl oxygen atoms shield the syn-face of the C(2)-C(3) double bond. endo-Addition of dienes to the anti-face provides an explanation for the high diastereofacial reactivity of the naphthoquinone 1d.
Regiospecific Reactions of Some Vinylogous Ketene Acetals with Haloquinones and Their Regioselective Formation by Dienolization
Brisson, Clement,Brassard, Paul
, p. 1810 - 1814 (2007/10/02)
Regiospecific reactions of simple 1,3-bis(trimethylsiloxy)-1,3-butadienes with 2,5- and 2,6-dichlorobenzoquinones gave chloronaphthoquinones which, by applying the appropriate vinylketene acetal, provided various monomethyl ethers of isomeric polyhydroxyanthraquinones.The first total synthesis of macrosporin (27) was obtained in this way and the proposed structure for "cajaquinone" (28) found to be incorrect.Simple syntheses of 2-hydroxy-3-methylanthraquinone (16), phomarin (19), soranjidiol (22) and other naturally occuring quinones are also described.The dienolization of 1-methoxy-2,4-pentanedione in the presence of chlorotrimethylsilane gave either 1- or 5-methoxy-2,4-bis(trimethylsiloxy)-1,3-pentadiene, depending upon the reaction conditions.Both dienes react with haloquinones, giving regiospecific products, e.g., tetra-O-methylerythrolaccin (35).
