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排序方式: 共有405条查询结果,搜索用时 15 毫秒
81.
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83.
Kumar Bhaskar Pal Aoxin Guo Mrinmoy Das Jiande Lee Gbor Bti Benjamin Rui Peng Yip Teck-Peng Loh Xue-Wei Liu 《Chemical science》2021,12(6):2209
Herein, we devised a method for stereoselective O-glycosylation using an Ir(i)-catalyst which enables both hydroalkoxylation and nucleophilic substitution of glycals with varying substituents at the C3 position. In this transformation, 2-deoxy-α-O-glycosides were acquired when glycals equipped with a notoriously poor leaving group at C3 were used; in contrast 2,3-unsaturated-α-O-glycosides were produced from glycals that bear a good leaving group at C3. Mechanistic studies indicate that both reactions proceed via the directing mechanism, through which the acceptor coordinates to the Ir(i) metal in the α-face-coordinated Ir(i)-glycal π-complex and then attacks the glycal that contains the O-glycosidic bond in a syn-addition manner. This protocol exhibits good functional group tolerance and is exemplified with the preparation of a library of oligosaccharides in moderate to high yields and with excellent stereoselectivities.Ir(i)-catalyzed α-selective O-glycosylation of glycals provided an access to both 2-deoxyglycosides and 2,3-unsaturated glycosides with a broad substrate scope. The underlying rationale of α-selectivity has been illustrated by the DFT study. 相似文献
84.
A chiral indium complex has been discovered to effect high enantioselectivities in the addition of allyltributyl stannanes to aldehydes. The allylation of a variety of aromatic, alpha,beta-unsaturated and aliphatic aldehydes resulted in good yields and high enantioselectivities (90-96% ee). 相似文献
85.
Ionic liquid [omim][PF6] has been demonstrated as an efficient and environmentally friendly reaction media as well as a promoter for the cyanosilylation of aldehydes under mild conditions. In addition, the recovered ionic liquid could be reused for subsequent runs with only a gradual decrease in activity. 相似文献
86.
Loh ED 《Physical review letters》1986,57(22):2865-2867
87.
Loh E 《Physical review letters》1985,55(22):2371-2374
88.
Aldol reaction under solvent-free conditions: highly stereoselective synthesis of 1,3-amino alcohols
[formula: see text] A method for the highly stereoselective synthesis of 1,3-amino alcohols based on the indium trichloride-catalyzed Mukaiyama aldol reaction of keto ester (R,S)-1 under solvent-free conditions has been developed. The high selectivity observed can be explained on the basis of the shielding of one face by a remote substituent. 相似文献
89.
Ilknur Yildirim Sarah Crotty Claas H. Loh Grit Festag Christine Weber Pier‐Francesco Caponi Michael Gottschaldt Matthias Westerhausen Ulrich S. Schubert 《Journal of polymer science. Part A, Polymer chemistry》2016,54(3):437-448
A simple and convenient method for the synthesis of end functionalized polylactides (PLAs) under mild conditions by ring opening polymerization (ROP) in the absence of potentially toxic catalysts is described. Various alcohols were used as initiators in combination with Ca[N(SiMe3)2]2(THF)2 as the precatalyst in THF at room temperature. Tailored end functionalities were obtained in a controlled fashion. Matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐ToF‐MS) and electrospray ionization quadrupole time of flight mass spectrometry (ESI‐Q‐ToF‐MS) analysis were performed to investigate the end groups. The results confirmed that the end group fidelity was maintained in the isolated PLAs. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 437–448 相似文献
90.