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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.
Completing the cyclooctane ring required 3 more carbon atoms that were supplied by a C2 fragment in an aldol addition and a Grignard C1 fragment (scheme 2).A Mukaiyama aldol addition (magnesium bromide / toluene) took place between aldehyde 7 and ketene silyl acetal 8 with 71% stereoselectivity to alcohol 9 which was protected as the TBS ether 10 (TBSOTf, 2,6-lutidine).
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 ]
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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 o-hydroxyphenacyl PPG has been introduced as an alternative with absorption band shifted closer towards the visible region, however it has slightly lower quantum yields of deprotection (generally 0.1-0.3) due to excited state proton transfer available as an alternative deactivation pathway. [29]
Hydrolysis of the dichloromethylene group in this dienone gives chloranil: [3] C 6 H 5 OH + 6 Cl 2 → C 6 Cl 6 O + 6 HCl C 6 Cl 6 O + H 2 O → C 6 Cl 4 O 2 + 2 HCl. Chloroanil serves as a hydrogen acceptor. It is more electrophilic than quinone itself. It is used for the aromatization reactions, such as the conversion of cyclohexadienes to ...