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Protecting Groups Handout A

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Chem 6352Protecting GroupsHydroxyl ProtectionMethyl EthersFormation:Stability: :Methyl ethers, with the exception of aryl methyl ethers, are often difficult to remove. However, there are , EtSH PhSe-Ph2P-Me3SiIStable to Acid and BaseCH2N2, SiO2 or HBF4NaH, MeI, THFMethylthiomethyl Ethers (MTM)Formation:Stability:Cleavage:MeSCH2 Cl, NaH, THFStable to base and mild acidHgCl2, CH3CN, H2OAgNO3, THF, H2O, baseOHOMeOOOMeOBzAlBr3, EtSHOOOHOBzTL 1987, 28, :TheMTMgroupisanicesubstitutedmethylethe rprotecting group that can be removed under neutral conditions employing the indicated of 1,2- and 1,3-diolsTrityl EthersFormation:Stability: :The trityl group usually goes on and comes off easily.

diols. It forms readily and is easily removed. Generally, the acetonide will form a dioxolane selectively over a dioxane. Ph Ph Ph Theprotectinggroupsthatmask1,2-and1,3-diols(formingeitherthe dioxolane or dioxane, respectively) are often referred to (PREFIX)ylidenes, where the prefix depends on the nature of R and R 1. OO OO RR1 RR 1 dioxolane ...

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