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The success of any organic synthesis depends on a number of factors, including the route, the conditions, and most importantly the reagents and catalysts. 2-OXAZOLYL]PYRIDINE”, ” e-EROS Encyclopedia of Reagents for Organic. Synthesis, Article Online Posting Date: November 18, 2,6-BIS[(4R,5R) e-EROS Encyclopedia of Reagents for Organic Synthesis. You will receive typeset proofs in PDF format via email direct from Wiley's typesetter.
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New Password. Your password has been changed. In contrast, iron is one of the most abundant metals on earth, and consequently one of the most inexpensive and environmentally friendly ones. Moreover, many iron salts and complexes are commercially available, or their applications are well described in the literature. Therefore, our aim was to find a method that utilized mild, relatively cheap reagents and flexible enough to allow the synthesis of glycosides.
To gain some preliminary information of this synthetically useful reaction, screening experiments were performed. It was carried out the reaction employing 1.
Firstly, it was tested different catalysts, among these, FeCl3 showed a positive result in terms of yield as compared with other catalysts Table 1 , entries Henceforth, it was focused our attention towards the use of iron salts for this transformation. The influence of different iron salts was further studied to check the reaction course. All these catalysts provide the corresponding glycoside 3 in traces, whereas FeCl3 was the only one to provide isolable yields of product Table 2 , entries In continuation of our optimization, it was next studied other factors including catalyst loading, reaction temperature and solvent.
This is due to the catalyst concentration which plays a fundamental role in this glycosylation reaction.
Finally, to further optimize the protocol, it was necessary to examine the effect of the solvent in promoting the reaction efficiency. The use of dichloromethane gave the higher yields as compared with other solvents Table 3 , entries Also, elevated temperature exhibited negative effect, which affords the byproduct formation as compared with room temperature Table 3 , entries 9 and 3.
Encyclopedia of Reagents for Organic Synthesis, 14 Volume Set, 2nd Edition
The results were summarized in Table 4. Our general reaction conditions involve the addition of alcohol 1.
In all cases, the product formation was observed as a single isomer in moderate to good yield Table 4 , entries It was speculated that FeCl3 would function as Lewis acid and thus promote the glycosylation. Unfortunately, however, our methodology fails. The mechanism of FeCl3 mediated glycosylation is still an intriguing subject of study.
Based on the literature report,18 it was proposed the plausible reaction pathways of the glycosylation Scheme 2.
Furthermore, the orthoester 4 would rearrange19 to give the glycosylated product 3. A great deal of interest has been laid in the application of synthesized compounds. Especially allyl glycoside, 3a is attractive due to the presence of the terminal double bond that is amenable to easy further functionalization leading to other molecules20 or selective deprotection of allyl group from glycoside 3a without affecting other functional groups on glycosides, which afford the anomeric alcohol 4c and this would be used as building blocks on carbohydrate arrays Scheme 3.
Column chromatography was performed using Merck silica gel mesh. For visualization, TLC plates were placed under acidic vanillin.
All solvents were used in dry conditions. General experimental procedure 3a-h Allyl or propargyl alcohol 1.
After completion of the reaction as monitored by thin-layer chromatography TLC , the reaction was diluted with dichloromethane and washed with water, and worked up in the usual manner. The crude product was purified by chromatography on silica gel ethyl acetate:hexane to afford the corresponding glycoside in good yield and with high selectivity. Conclusions In conclusion, our methodology has several notable advantages such as mild reaction conditions that make use of a reagent of relatively low toxicity, low-catalyst loading, good yields and high anomeric selectivity.
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If you do not receive an email within 10 minutes, your email address may not be registered, and you may need to create a new Wiley Online Library account. Tetrahedron , 58, Lubin-Germain, N. Adesomoju, A.