F. Ono, H. Takenaka, T. Fujikawa, M. Mori, T. Sato, Synthesis, 2009, 1318-1322. 0000001397 00000 n
[8][9] Although selective deprotections have been achieved under many different conditions, some procedures, outlined below, are more reliable. 29647 Views Silyl Protective Groups. 0000003074 00000 n
A diol can be converted to cyclic ether by using an acid catalyst, this is diol cyclization. 0000000991 00000 n
This time we're going to use, instead of a diol, we're going to use something with two SH groups instead here, so a dithiol here. An example in the synthesis of trans-cyclohexanediol[3] or by microreactor:[4]. Examples include 1,2-ethanediol or ethylene glycol HO−(CH2)2−OH, a common ingredient of antifreeze products. 2000, 41, 4281. ", Higashibayashi, S.; Shinko, K.; Ishizu, T.; Hashimoto, K.; Shirahama, H.; Nakata, M. "Selective deprotection of, Silicon-based Protection of the Hydroxyl Group, https://en.wikipedia.org/w/index.php?title=Silyl_ether&oldid=886295800, Creative Commons Attribution-ShareAlike License, 10 mol% 10-CSA, 1:1 MeOH:DCM, −20 or 0 °C; deprotects a primary TBS group within two hours at 0; if CSA is replaced by. "Protection of hydroxyl groups as, Corey, E. J.; Cho, H.; Rücker C.; Hua, D. H. "Studies with trialkylsilyltriflates: new syntheses and applications.". Another example is propane-1,2-diol, or alpha propylene glycol, HO−CH2−CH(OH)−CH3, used in the food and medicine industry, as well as a relatively non-poisonous antifreeze product. So we can use an acidic environment here. 1,3-Diols can be prepared by hydration of α,β-unsaturated ketones and aldehydes. Corey, E. J.; Venkateswarlu, A. In acidic media, the relative resistance is: In basic media, the relative resistance is: It is possible to monosilylate a symmetrical diol, although this is known to be problematic occasionally. So the first thing we could do, to do this transformation, is to form a thioacetal. 1,3-Diols are described as syn or anti depending on the relative stereochemistries of the carbon atoms bearing the hydroxyl functional groups. Fluoride-based deprotections deprotect electron-poor silyl groups faster than electron-rich silyl groups. Holton, R. A. et al. In a vicinal diol, the two hydroxyl groups occupy vicinal positions, that is, they are attached to adjacent atoms. So it's going to be, again, analogous to the formation of an acetal. An aliphatic diol is also called a glycol. Easily removed with -OH or -H Stable to Base Phosgene, pyridine Triphosgene, pyridine Carbonyl diimidazole OH R R1 HO OO R R1 O. p-Methoxybenzyl (PMB) Protective Group. Silyl ethers are a group of chemical compounds which contain a silicon atom covalently bonded to an alkoxy group. ", Crouch, R. D. "Selective monodeprotection of bis-silyl ethers. Another route involves the hydroformylation of epoxides followed by hydrogenation of the aldehyde. The most common industrial diol is ethylene glycol. 0000006249 00000 n
Silyl ethers are usually used as protecting groups for alcohols in organic synthesis. This page was last edited on 5 March 2019, at 11:19. A diol is a chemical compound containing two hydroxyl groups (−OH groups). A common hindered base for use with silyl triflates is 2,6-lutidine. Six-membered ring: thermodynamically favored Five-membered ring: kinetically favored General Mechanism Diols such as ethylene glycol are used as co-monomers in polymerization reactions forming polymers including some polyesters and polyurethanes. 0000002257 00000 n
02 February, 2014 / by webmaster / in Reactions. This pairing of functional groups is pervasive, and many subcategories have been identified. (a) Propose a mechanism for the formation of this protected diol. For example, carbonic acid ((HO)2C=O) is unstable and has a tendency to convert to carbon dioxide (CO2) and water (H2O). Completion of the C and D rings. There is some evidence that some silyl deprotections proceed via hypervalent silicon species. ���u4(bi@Fa� ����A��@�&ǔ�@����Qf�e�a�&���=B�QWzÇ�*���Lk4ffPg`H��_��f��43�. 0000000636 00000 n
Both the functional groups could react with a Grignard Reagent. Provided that there are enough carbon atoms that the angle strain is not too much, a cyclic ether can be formed. Unfortunately, some optimization is inevitably required and it is often necessary to run deprotections partway and recycle material. Protecting Groups of 1,2- or 1,3-Dihydroxyl Groups Consider the formation of acetal (ketal) from diol and aldehyde (ketone)! Common silyl ethers are: trimethylsilyl (TMS), tert-butyldiphenylsilyl (TBDPS), tert-butyldimethylsilyl (TBS/TBDMS) and triisopropylsilyl (TIPS). ", Nelson, T. D.; Crouch, R. D. "Selective deprotection of silyl ethers.