Total Synthesis of (+)‐Davidiin

Bioinspired Total Synthesis of (−)‐Vescalin: A Nonahydroxytriphenoylated C‐Glucosidic Ellagitannin

“…[15] Thei ntramolecular oxidative coupling of parabenzylated galloyl groups was first implemented under such reaction conditions by Yamada and his co-workers,w ho successfully applied it in the total synthesis of several glucopyranosic HHDP-bearing ellagitannins. [16] We also relied on the same method to forge a D-type 2,3-O-(S)-HHDP-bearing intermediate in the synthesis of 9.…”

“…This precursor 16 resembles liquidambin (6,Scheme 1) in several structural criteria, including the C1 aldehyde function, the 5-O-galloyl group,a nd the 2,3-O-(S)-HHDP unit, which are both adequately protected in anticipation of the Cglucosidation step (i.e., with fluoride-labile silyl groups in meta-positions) and the NHTP-forming terarylation step (i.e., with benzyl groups in para-positions as per the method reported by Yamada and co-workers [16] ). Moreover,the cyclic benzylidene protecting group is auseful surrogate of the 4,6-O-HHDP unit of 6,w hich should contribute to maintain the open-chain glucose core and the 2,3-O-HHDP unit of 16 in an appropriate conformational status for facilitating the intramolecular C-arylglucosidation reaction.…”

“…Ther esulting A-type benzylic alcohol 17 was thus generated as a1:2 a/b epimeric mixture, which was separated by column chromatography to furnish a-17 and b-17 in 25 and 56 %yields,respectively.With the major epimer b-17 in hand, we were thus ready to take on the focal and last C À Cb ond-forming step toward 1,a sp er the Wynberg-Feringa-Yamada oxidative coupling approach (Table 1). [15,16] Initial attempts under standard Yamada conditions in MeOH [16e] led to an undesired n-butylaminocontaining oxidized derivative 18 (not shown, see the Supporting Information), the yield of which increased from about 15 to 49 %u pon changing the solvent to MeCN (entries 1a nd 2). Theu se of the bidentate tetramethylethylenediamine (TMEDA) in MeOH provoked full degradation of the material (entry 3).…”

Total Syntheses of Laevigatins A and E

“…[14] Thus, diesterification of diol 12 with carboxylic acid 13 [20] using EDCI {1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide} and DMAP [4-(dimethylamino)pyridine] gave the corresponding bisgallate. In this reaction, the choice of solvent was crucial; CH 2 Cl 2 gave a selectivity of 17:3, whereas MeCN [16] gave a selectivity of 1:1. The CuCl 2 ·nBuNH 2 -mediated oxidative aryl-aryl coupling of 10 gave the corresponding biaryl compound, [20] the four hydroxy groups of which were then benzylated.…”

“…Although a wide variety of biological activities have been reported for the ellagitannins, [1,2,9] the elucidation of their structure-activity relationships has been a problem due to the difficulty of obtaining a complete collection of systematically related analogues from nature. Fortunately, the synthesis of monomeric ellagitannins and their artificial analogues has progressed significantly, and much knowledge has been accumulated, [11][12][13][14][15][16][17][18][19][20][21][22][23][24] although the amounts of the compounds synthesized have been small in many cases. A considerable number of characterized compounds, which could be isolated only in trace amounts, have been left unexplored.…”