Types of Protecting Groups

Question 1

ester protecting groups

Answer 1

acid chloride (AcCl)

benzoyl chloride (BzCl)

Question 2

ether protecting groups

Answer 2

benzyl bromide (BnBr)

silyl ether (R’3SiCl)

Question 3

AcCl protection

Answer 3

excess AcCl, pyr, Rm T, CH2Cl to protect all OHs

Question 4

AcCl deprotection

Answer 4

use CH3OH/CH3O (if OH used acid byproduct formed)

if only 1 equiv used, C1 deprotected b/c more E+

get alpha/beta b/c C1 resonance top/bottom atk

Question 5

BzCl protection

Answer 5

BzCl, pyr, Rm T, CH2Cl2 (bulky so protects 1º>2º)

if 1 equiv protects C6-OH

Question 6

BzCl deprotection

Answer 6

smaller base than with AcCl to approach bulky group

KOH, EtOH, Rm T

Question 7

BnBr protection

Answer 7

BnBr, NaH, 0ºC, THF (str base push rxn forward)

polar aprotic solvent so str base isn’t neutralized

if 1 equiv protects C6-OH

Question 8

BnBr deprotection

Answer 8

H2, Pd/C, EtOH catalytic hydrogenation

toluene

alipathic (alkane) ethers not reduced

Question 9

silyl ether protection

Answer 9

if R’ methyl then TMS-Cl

if R’ Ph, Ph, t-butyl then TBDPS-Cl

pyr/TEA

Question 10

silyl ether deprotection

Answer 10

TBAF

F- strong affinity for silicon

Question 11

how to get C6-OH free

Answer 11

1st protect w/ BnBr

2nd excess AcCl

3rd deprotect BnBr w/ H2, Pd/C, EtOH