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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]
Orthogonal protection is a strategy allowing the specific deprotection of one protective group in a multiply-protected structure. For example, the amino acid tyrosine could be protected as a benzyl ester on the carboxyl group, a fluorenylmethylenoxy carbamate on the amine group, and a tert-butyl ether on the phenol
For example, (C 6 H 5)(CH 3) 2 C + is referred to as a "benzylic" carbocation. The benzyl free radical has the formula C 6 H 5 CH 2 • . The benzyl cation or phenylcarbenium ion is the carbocation with formula C 6 H 5 CH + 2 ; the benzyl anion or phenylmethanide ion is the carbanion with the formula C 6 H 5 CH − 2 .
Sequential treatment with trimethylsilyl iodide then methanol can also be used for Boc deprotection, [7] [8] especially where other deprotection methods are too harsh for the substrate. [9] The mechanism involves silylation of the carbonyl oxygen and elimination of tert -butyl iodide ( 1 ), methanolysis of the silyl ester to the carbamic acid ...
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A variety of approaches to protection and deprotection of carbonyls [6] including as dioxolanes [7] are known. For example, consider the compound methyl cyclohexanone-4-carboxylate, where lithium aluminium hydride reduction will produce 4-hydroxymethylcyclohexanol.
Deprotection of Boc-protected amines can be achieved using trimethylsilyl trifluoromethanesulfonate and triethylamine or 2,6-lutidine. [ 7 ] [ 8 ] TMSOTf is also a useful reagent to replace metal-halogen bonds with a covalent M-O(SO2CF3) bond, the by-product being the highly volatile TMSCl which is easily removed.
An example of 1,4-addition reaction is the addition of hydrogen chloride to form chlorohydroquinone: 1,4-addition reaction of quinone with hydrogen chloride to produce chlorohydroquinone. Quinones can undergo Diels–Alder reactions. [10] The quinone acts as the dienophile and reacts with a diene at a carbon-carbon double bond.