CHEM 335 Chapter Notes - Chapter 7: Keta, Acetic Anhydride, The Boc Group
1 Apr 2016
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Alcohols give two major reactions for protecting groups: To revert back to alcohol conditions may have to be harsh. Have ether like qualities but convert easily back to alcohol. Why we use them: to mask functionality in order to carry out a particular transformation reaction, to overcome chemoselectivity issues (ie. two oh groups: how to differenetiate them, prevent side reactions with incompatible functionality on molecule. Classes of reactants: acids (protic or lewis acids, bases, nucelophiles, organometallics (grignards, lithiums, hydrides, oxidizing agents, catalytic hydrogenation (h2- pd/c) (1) silyl protecting groups: Aqueous cleavage (h2o, mild h+, or mild base) Increasing steric demand of r leads to greater stability of silyl ether. Now more stable to acids, bases and most nucelophiles cleavage by f- anion. Tbdpsi tbuph2si also bulky and stable in most conditions (2) protecting groups for alcohols ethers. Stable to most classes of reagents cleaved by brb3 (strong lewis acid: dihydropyran:
