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Protecting Groups: How They Work TargetM olecule: R eagents: OH Na and Br OH W e can'tsim ply m ix the reagentshere:deprotonation occursfaster than alkylation (acid base reaction, think aboutpK a differences) Na Br OH + Br O Na + So, w e protectthe alcoholasan ether first, and w e can successfully alkylate: Br OH 1. H 2 SO 4 2. C H 2 =C(CH 3 ) 2 Br O t Bu Na O t Bu H 3 O + /H 2 O OH + t BuO H

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Page 1: Protecting Groups: How They Work. Protecting Groups: Alcohol Alkylation Alcohol Groups do not “Survive” Many Organic Reactions Alkylation (Ether Formation)

Protecting Groups: How They Work

Target Molecule:

Reagents:

OH

Na and Br OH

We can't simply mix the reagents here: deprotonation occurs fasterthan alkylation (acid base reaction, think about pKa differences)

Na Br OH+ Br ONa+

So, we protect the alcohol as an ether first, and we can successfully alkylate:

Br OH1. H2SO4

2. CH2=C(CH3)2 Br OtBuNa

OtBu H3O+/H2OOH

+ tBuOH

Page 2: Protecting Groups: How They Work. Protecting Groups: Alcohol Alkylation Alcohol Groups do not “Survive” Many Organic Reactions Alkylation (Ether Formation)
Page 3: Protecting Groups: How They Work. Protecting Groups: Alcohol Alkylation Alcohol Groups do not “Survive” Many Organic Reactions Alkylation (Ether Formation)
Page 4: Protecting Groups: How They Work. Protecting Groups: Alcohol Alkylation Alcohol Groups do not “Survive” Many Organic Reactions Alkylation (Ether Formation)

Protecting Groups: Alcohol Alkylation

• Alcohol Groups do not “Survive” Many Organic Reactions

• Alkylation (Ether Formation) Protects OH’s During Synthesis

• Can Remove the Protecting Group w/ Dilute Aqueous Acid

• Generally Dissolve Alcohol in Acid, THEN add Isobutylene

• Addition in this Manner Minimizes Isobutylene Dimerization

• Let’s See Why We Might Want to Use a Protecting Group

OH +OH2SO4

Page 5: Protecting Groups: How They Work. Protecting Groups: Alcohol Alkylation Alcohol Groups do not “Survive” Many Organic Reactions Alkylation (Ether Formation)
Page 6: Protecting Groups: How They Work. Protecting Groups: Alcohol Alkylation Alcohol Groups do not “Survive” Many Organic Reactions Alkylation (Ether Formation)
Page 7: Protecting Groups: How They Work. Protecting Groups: Alcohol Alkylation Alcohol Groups do not “Survive” Many Organic Reactions Alkylation (Ether Formation)
Page 8: Protecting Groups: How They Work. Protecting Groups: Alcohol Alkylation Alcohol Groups do not “Survive” Many Organic Reactions Alkylation (Ether Formation)
Page 9: Protecting Groups: How They Work. Protecting Groups: Alcohol Alkylation Alcohol Groups do not “Survive” Many Organic Reactions Alkylation (Ether Formation)
Page 10: Protecting Groups: How They Work. Protecting Groups: Alcohol Alkylation Alcohol Groups do not “Survive” Many Organic Reactions Alkylation (Ether Formation)
Page 11: Protecting Groups: How They Work. Protecting Groups: Alcohol Alkylation Alcohol Groups do not “Survive” Many Organic Reactions Alkylation (Ether Formation)
Page 12: Protecting Groups: How They Work. Protecting Groups: Alcohol Alkylation Alcohol Groups do not “Survive” Many Organic Reactions Alkylation (Ether Formation)
Page 13: Protecting Groups: How They Work. Protecting Groups: Alcohol Alkylation Alcohol Groups do not “Survive” Many Organic Reactions Alkylation (Ether Formation)
Page 14: Protecting Groups: How They Work. Protecting Groups: Alcohol Alkylation Alcohol Groups do not “Survive” Many Organic Reactions Alkylation (Ether Formation)
Page 15: Protecting Groups: How They Work. Protecting Groups: Alcohol Alkylation Alcohol Groups do not “Survive” Many Organic Reactions Alkylation (Ether Formation)
Page 16: Protecting Groups: How They Work. Protecting Groups: Alcohol Alkylation Alcohol Groups do not “Survive” Many Organic Reactions Alkylation (Ether Formation)

Protecting Groups: Silyl Ethers

OH + Cl Si

Me

Me

tBuPyridine

DMF

tert-Butylchlorodimethylsilane

Si

Me

Me

tBuO

O-TBDMS

• Silyl Ethers Stable Over a 4-12 pH Range (Acidic and Basic)

• Can Survive Conditions of Many Organic Reactions

• Typically Removed w/ Flouride Source (NBu4F; aka TBAF)

• Silyl Ethers More Volatile Than Alcohols (GC Applications)

Page 17: Protecting Groups: How They Work. Protecting Groups: Alcohol Alkylation Alcohol Groups do not “Survive” Many Organic Reactions Alkylation (Ether Formation)
Page 18: Protecting Groups: How They Work. Protecting Groups: Alcohol Alkylation Alcohol Groups do not “Survive” Many Organic Reactions Alkylation (Ether Formation)
Page 19: Protecting Groups: How They Work. Protecting Groups: Alcohol Alkylation Alcohol Groups do not “Survive” Many Organic Reactions Alkylation (Ether Formation)
Page 20: Protecting Groups: How They Work. Protecting Groups: Alcohol Alkylation Alcohol Groups do not “Survive” Many Organic Reactions Alkylation (Ether Formation)
Page 21: Protecting Groups: How They Work. Protecting Groups: Alcohol Alkylation Alcohol Groups do not “Survive” Many Organic Reactions Alkylation (Ether Formation)
Page 22: Protecting Groups: How They Work. Protecting Groups: Alcohol Alkylation Alcohol Groups do not “Survive” Many Organic Reactions Alkylation (Ether Formation)
Page 23: Protecting Groups: How They Work. Protecting Groups: Alcohol Alkylation Alcohol Groups do not “Survive” Many Organic Reactions Alkylation (Ether Formation)
Page 24: Protecting Groups: How They Work. Protecting Groups: Alcohol Alkylation Alcohol Groups do not “Survive” Many Organic Reactions Alkylation (Ether Formation)
Page 25: Protecting Groups: How They Work. Protecting Groups: Alcohol Alkylation Alcohol Groups do not “Survive” Many Organic Reactions Alkylation (Ether Formation)
Page 26: Protecting Groups: How They Work. Protecting Groups: Alcohol Alkylation Alcohol Groups do not “Survive” Many Organic Reactions Alkylation (Ether Formation)
Page 27: Protecting Groups: How They Work. Protecting Groups: Alcohol Alkylation Alcohol Groups do not “Survive” Many Organic Reactions Alkylation (Ether Formation)
Page 28: Protecting Groups: How They Work. Protecting Groups: Alcohol Alkylation Alcohol Groups do not “Survive” Many Organic Reactions Alkylation (Ether Formation)
Page 29: Protecting Groups: How They Work. Protecting Groups: Alcohol Alkylation Alcohol Groups do not “Survive” Many Organic Reactions Alkylation (Ether Formation)
Page 30: Protecting Groups: How They Work. Protecting Groups: Alcohol Alkylation Alcohol Groups do not “Survive” Many Organic Reactions Alkylation (Ether Formation)
Page 31: Protecting Groups: How They Work. Protecting Groups: Alcohol Alkylation Alcohol Groups do not “Survive” Many Organic Reactions Alkylation (Ether Formation)
Page 32: Protecting Groups: How They Work. Protecting Groups: Alcohol Alkylation Alcohol Groups do not “Survive” Many Organic Reactions Alkylation (Ether Formation)
Page 33: Protecting Groups: How They Work. Protecting Groups: Alcohol Alkylation Alcohol Groups do not “Survive” Many Organic Reactions Alkylation (Ether Formation)
Page 34: Protecting Groups: How They Work. Protecting Groups: Alcohol Alkylation Alcohol Groups do not “Survive” Many Organic Reactions Alkylation (Ether Formation)
Page 35: Protecting Groups: How They Work. Protecting Groups: Alcohol Alkylation Alcohol Groups do not “Survive” Many Organic Reactions Alkylation (Ether Formation)
Page 36: Protecting Groups: How They Work. Protecting Groups: Alcohol Alkylation Alcohol Groups do not “Survive” Many Organic Reactions Alkylation (Ether Formation)
Page 37: Protecting Groups: How They Work. Protecting Groups: Alcohol Alkylation Alcohol Groups do not “Survive” Many Organic Reactions Alkylation (Ether Formation)
Page 38: Protecting Groups: How They Work. Protecting Groups: Alcohol Alkylation Alcohol Groups do not “Survive” Many Organic Reactions Alkylation (Ether Formation)
Page 39: Protecting Groups: How They Work. Protecting Groups: Alcohol Alkylation Alcohol Groups do not “Survive” Many Organic Reactions Alkylation (Ether Formation)
Page 40: Protecting Groups: How They Work. Protecting Groups: Alcohol Alkylation Alcohol Groups do not “Survive” Many Organic Reactions Alkylation (Ether Formation)
Page 41: Protecting Groups: How They Work. Protecting Groups: Alcohol Alkylation Alcohol Groups do not “Survive” Many Organic Reactions Alkylation (Ether Formation)
Page 42: Protecting Groups: How They Work. Protecting Groups: Alcohol Alkylation Alcohol Groups do not “Survive” Many Organic Reactions Alkylation (Ether Formation)
Page 43: Protecting Groups: How They Work. Protecting Groups: Alcohol Alkylation Alcohol Groups do not “Survive” Many Organic Reactions Alkylation (Ether Formation)
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