30531-69-2Relevant academic research and scientific papers
Ruthenium(II)-Catalyzed Homocoupling of Weakly Coordinating Sulfoxonium Ylides via C?H Activation/Annulations: Synthesis of Functionalized Isocoumarins
Zhou, Ming-Dong,Peng, Zhen,Wang, He,Wang, Zhao-Hui,Hao, Da-Jin,Li, Lei
, p. 5191 - 5197 (2019/11/13)
Homocoupling of weakly coordinating sulfoxonium ylides was accomplished via ruthenium (II) catalyzed C?H activation process. This strategy provides a convenient, efficient and step-economic method to access 3-substituted isocoumarins with good functional
Hydrogen-Bonding-Assisted Exogenous Nucleophilic Reagent Effect for β-Selective Glycosylation of Rare 3-Amino Sugars
Zeng, Jing,Wang, Ruobin,Zhang, Shuxin,Fang, Jing,Liu, Shanshan,Sun, Guangfei,Xu, Bingbing,Xiao, Ying,Fu, Dengxian,Zhang, Wenqi,Hu, Yixin,Wan, Qian
supporting information, p. 8509 - 8515 (2019/06/13)
Challenges for stereoselective glycosylation of deoxy sugars are notorious in carbohydrate chemistry. We herein report a novel strategy for the construction of the less investigated β-glycosidic bonds of 3,5-trans-3-amino-2,3,6-trideoxy sugars (3,5-trans-3-ADSs), which constitute the core structure of several biologically important antibiotics. Current protocol leverages a C-3 axial sulfonamide group in 3,5-trans-3-ADSs as a hydrogen-bond (H-bond) donor and repurposes substoichiometric phosphine oxide as an exogenous nucleophilic reagent (exNu) to establish an intramolecular H-bond between the former and the derived α-oxyphosphonium ion. This pivotal interaction stabilizes the α-face-covered intermediate to inhibit the formation of the more reactive β-intermediate, thereby yielding reversed β-selectivity, which is unconventional for an exNu-mediated glycosylation system. A wide range of substrates was accommodated, and good to excellent β-selectivities were ensured by this H-bonding-assisted exNu effect. The robustness of the current strategy was further attested by the architectural modification of natural products and drugs containing 3,5-trans-3-ADSs, as well as the synthesis of a trisaccharide unit in avidinorubicin.
Gold(i)-catalyzed C-glycosylation of glycosyl: Ortho -alkynylbenzoates: The role of the moisture sequestered by molecular sieves
Chen, Xiaoping,Wang, Qiaoling,Yu, Biao
supporting information, p. 12183 - 12186 (2016/10/21)
C-Glycosylation of glycosyl ortho-hexynylbenzoates with allyltrimethylsilane or silyl enol ethers could proceed smoothly under the catalysis of Ph3PAuNTf2 to provide the corresponding C-glycosides in high yields and stereoselectivity, wherein the moisture sequestered by the molecular sieves was disclosed to play a critical role in the gold(i)-catalytic cycle.
Highly stereoselective β-mannopyranosylation via the 1-α-glycosyloxy-isochromenylium-4-gold(I) intermediates
Zhu, Yugen,Yu, Biao
supporting information, p. 8771 - 8780 (2015/06/08)
While the gold(I)-catalyzed glycosylation reaction with 4,6-O-benzylidene tethered mannosyl ortho-alkynylbenzoates as donors falls squarely into the category of the Crich-type β-selective mannosylation when Ph3PAuOTf is used as the catalyst, in that the mannosyl α-triflates are invoked, replacement of the -OTf in the gold(I) complex with less nucleophilic counter anions (i.e., -NTf2, -SbF6, -BF4, and -BAr4F) leads to complete loss of β-selectivity with the mannosyl ortho-alkynylbenzoate β-donors. Nevertheless, with the α-donors, the mannosylation reactions under the catalysis of Ph3PAuBAr4F (BAr4F=tetrakis[3,5-bis(trifluoromethyl)phenyl]borate) are especially highly β-selective and accommodate a broad scope of substrates; these include glycosylation with mannosyl donors installed with a bulky TBS group at O3, donors bearing 4,6-di-O-benzoyl groups, and acceptors known as sterically unmatched or hindered. For the ortho-alkynylbenzoate β-donors, an anomerization and glycosylation sequence can also ensure the highly β-selective mannosylation. The 1-α-mannosyloxy-isochromenylium-4-gold(I) complex (Cα), readily generated upon activation of the α-mannosyl ortho-alkynylbenzoate (1 α) with Ph3PAuBAr4F at -35 C, was well characterized by NMR spectroscopy; the occurrence of this species accounts for the high β-selectivity in the present mannosylation.
Mechanistic insights into the gold(I)-Catalyzed activation of glycosyl Ortho -Alkynylbenzoates for Glycosidation
Tang, Yu,Li, Jiakun,Zhu, Yugen,Li, Yao,Yu, Biao
supporting information, p. 18396 - 18405 (2014/01/06)
Anomerization, which involves cleavage and formation of the anomeric C-O bond, is of fundamental importance in the carbohydrate chemistry. Herein, the unexpected gold(I)-catalyzed anomerization of glycosyl ortho-alkynylbenzoates has been studied in detail. Especially, crossover experiments in the presence of an exogenous isochromen-4-yl gold(I) complex confirm that the anomerization proceeds via the exocleavage mechanism, involving (surprisingly) the addition of the isochromen-4-yl gold(I) complex onto a sugar oxocarbenium (or dioxolenium) and an elimination of LAu+ from the vinyl gold(I) complex. The inhibitory effect of the exogenous isochromen-4-yl gold(I) complex when in stoichiometric amount on the anomerization has guided us to disclose an isochromen-4-yl gem-gold(I) complex, which is inactive in catalysis but in equilibrium with the monogold(I) complex and the LAu+ catalyst. The proposed key intermediate in the anomerization, a transient glycosyloxypyrylium species, is successfully trapped via a cycloaddition reaction with n-butyl vinyl ether as a dienophile. SN2-like substitution of the initially formed glycosyloxypyrylium intermediate has then been achieved to a large extent via charging with acceptors in an excess amount to lead to the corresponding glycosides in a stereoselective manner.
On homogeneous gold/palladium catalytic systems
Hashmi, A. Stephen K.,Lothschuetz, Christian,Doepp, Rene,Ackermann, Martin,De Buck Becker, Janosc,Rudolph, Matthias,Scholz, Christian,Rominger, Frank
, p. 133 - 147 (2012/04/10)
Two substrates containing an aryl iodide and an allenoate ester were prepared and the goldinduced cycloisomerisation to vinylgold(I) species and their proto-deauration as well as the intramolecular palladium-catalysed cross-coupling reactions were investigated. Switching to catalytic amounts of gold and palladium and stoichiometric amounts of silver did indeed furnish the product of a cycloisomerisation/ intramolecular cross-coupling. Control experiments revealed that silver cannot substitute for gold or palladium in these reactions, but a different palladium catalyst in a different oxidation state also afforded the cycloisomerisation/intramolecular crosscoupling products in only slightly reduced yields. By ICP analysis the palladium was shown to contain gold only at the sub-ppm level. This shows how carefully results obtained with such systems have to be interpreted. Then a series of allylic and benzylic o-alkynylbenzoates were investigated in gold-and palladium-catalysed reactions. For esters of benzyl alcohol and cinnamyl alcohol no palladium co-catalyst was needed for the conversion. All reagents were thoroughly checked for palladium traces by ICP analysis in order to thoroughly exclude a gold/palladium cocatalysis. Optimisation of the gold complex, counter ion and solvent showed that gold(I) isonitrile precatalysts and silver triflate as activator in dioxane are suitable to convert a number of substrates with aryl, alkyl and even cyclopropyl substituents. Crossover experiments proved an intermolecular allyl transfer.
Gold-catalyzed transesterification of ortho-alkynylbenzoic acid esters: a novel protecting group for alcohols and phenols
Umetsu, Kazuteru,Asao, Naoki
body text, p. 7046 - 7049 (2009/04/07)
Treatment of ortho-alkynylbenzoic acid esters with excess amounts of EtOH in the presence of a gold catalyst results in the liberation of alcohols or phenols in high yields under mild conditions. The protection of alcohols and phenols proceeds smoothly by use of ortho-alkynylbenzoic acid or ortho-iodobenzoyl chloride. Highly chemoselective deprotections are described.
