Unformatted text preview: pair followed by SN1 type ionization to form a carbocation that is trapped via halide addition. • Ethers as Protecting Groups : Because they are easily formed and cleaved, tert-butyl ethers can serve as “protecting groups.” For example, the attempted methylation of HC ≡ CCH 2 OH gives mostly the O-methylated product. Selective methylation at the acetylenic terminus requires that we first protect the hydroxyl group as the tert-butyl ether to give HC ≡ CCH 2 O t Bu. Now, with the acidic hydroxyl proton “masked”, we can methylate the acetylenic carbon under standard conditions (NaH, CH 3 I, DMSO). After this methylation is performed, one can “unmask” the hydroxyl moiety by cleaving the tert-butyl ether using aqueous acid to give H 3 CC ≡ CCH 2 OH....
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- Fall '08
- acetylenic terminus, corresponding alkyl halides