This preview shows page 1. Sign up to view the full content.
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....
View Full Document
- Fall '08