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2,3-Dichloro-5,6-dicyano-1,4-benzoquinone (or DDQ) is the chemical reagent with formula C 6 Cl 2 (CN) 2 O 2. This oxidant is useful for the dehydrogenation of alcohols, [3] phenols, [4] and steroid ketones. [5] DDQ decomposes in water, but is stable in aqueous mineral acid. [6]
The use of protective groups is pervasive but not without criticism. [103] In practical terms their use adds two steps (protection-deprotection sequence) to a synthesis, either or both of which can dramatically lower chemical yield. Crucially, added complexity impedes the use of synthetic total synthesis in drug discovery.
p-Methoxybenzyl (PMB) is used as a protecting group for alcohols in organic synthesis (4-Methoxybenzylthiol is used to protect thiols). The p -methoxybenzyl group Strong base such as powdered potassium hydroxide or sodium hydride and p -methoxybenzyl halide (chloride or bromide) [ 14 ] [ 15 ]
Typically, selective cleavage of a PMB ether in the presence of a benzyl ether uses strong stoichiometric oxidants such as 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) or ceric ammonium nitrate (CAN). PMB ethers are far more susceptible to oxidation than benzyl ethers since they are more electron-rich.
The glycosyl acceptor is then tethered at the benzylic position of the PMB protecting group in the presence of 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). The anomeric leaving group (Y) is then activated, and the developing oxocarbenium ion is captured by the tethered aglycon alcohol (OR) to give 1,2- cis β-glycoside product.
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2,3-Dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) is often the reagent of choice. DDQ and an acid catalyst has been used to synthesise a steroid with a phenanthrene core by oxidation accompanied by a double methyl migration. [9] In the process, DDQ is itself reduced into an aromatic hydroquinone product.