Organic Chemistry

778 CHAPTER 18 Carbonyl Compounds II

5. Protecting groups (Section 18.8).

a. Aldehydesand ketonescan be protected by being converted to acetals:

b. The OH group of an alcoholcan be protected by being converted to a TMS ether:

c. The OH group of a carboxylic acidcan be protected by being converted to an ester:

d.An amino groupcan be protected by being converted to an amide:

6. Reaction of an aldehydeor a ketonewith a thiol forms a thioacetal or a thioketal (Section 18.9):


7. Desulfurization of thioacetalsand thioketalsforms alkanes (Section 18.9):


8. Reaction of an aldehydeor a ketonewith a phosphonium ylide (a Wittig reaction) forms an alkene (Section 18.10):


9. Reactions of -unsaturated aldehydesand ketoneswith nucleophiles (Section 18.13):

Nucleophiles that are weak bases ( RSH, ) and form conjugate addition products. Nucleophiles that are

strong bases (RLi, RMgBr, and ) form direct addition products with reactive carbonyl groups and conjugate addition products

with less reactive carbonyl groups.

H-

• CN, RNH 2 ,Br- R 2 CuLi

O

RCH CHCR′

OH

RCH

direct addition

conjugate addition

CHCR′

O

Nu

RCHCH 2 CR′

+ NuH

Nu

a,b

C

+ (C 6 H 5 ) 3 PC

R

R

C(C+ 6 H 5 ) 3 PO

R R

O

CC

RR′ RR′

H 2

Raney Ni

SR′′

SR′′

RRC ′ RRCH 2 ′

SR′′

SR′′

RRC ′ + H 2 O

O

R

+ 2 R′′SH

R′

HCl

C

R ++HCl

O

RCl

O

R NHR

NH 2 CC

++CH 3 OH H 2 O

O

ROH

O

R OCH 3

HCl

excess

CC

ROH+ (CH 3 ) 3 SiCl R OSi(CH 3 ) 3

(CH 3 CH 2 ) 3 N

+ HOCH 2 CH 2 OH + H 2 O

HCl

O

C

R R R R

C

O O