Page 1049 - Advanced Organic Chemistry Part A - Structure and Mechanisms, 5th ed (2007) - Carey _ Sundberg

O O 1033
O O
n – Bu SnH
3
SECTION 11.4
O
SePh O Free Radical Addition
Reactions
74%
Some other examples of acyl radical additions are discussed in Section 11.4.5.
The chain addition of formamide to alkenes is a closely related reaction and results
in the formation of primary amides. 170 The reaction is carried out with irradiation in
acetone. The photoexcited acetone initiates the chain reaction by abstracting hydrogen
from formamide.
∗
O O
hv
CH 3 CCH 3 CH 3 CCH 3
∗
O O O OH
.
CH 3 CCH 3 + HCNH 2 . CNH 2 + CH 3 CCH 3
O O
. + H 2 C CHR H 2 NCCH 2 CHR
.
CNH 2
O O O O
. CHR + H 2 NCCH 2 CH 2 R + . CNH 2
H 2 NCCH 2 HCNH 2
11.4.4. Addition of Thiols and Thiocarboxylic Acids

The addition of S−H compounds to alkenes by a radical chain mechanism is a
quite general and efficient reaction. 171 The mechanism is analogous to that for hydrogen
bromide addition. The energetics of both the hydrogen abstraction and addition steps
are favorable. The reaction exhibits anti-Markovnikov regioselectivity.

. .
In + R′SH InH + R′S
R′S . + H C CHR R′SCH CHR
2 2 .
R′SCH CHR + R′SH R′SCH CH R + R′S .
2
2
2 .
The preferred stereochemistry of addition to cyclic alkenes is anti, 172 but the additions
are not as highly stereoselective as for hydrogen bromide addition.

11.4.5. Examples of Radical Addition Reactions
Scheme 11.5 gives some examples of these radical addition reactions. Entries 1
to 3 show anti-Markovnikov addition of HBr. The reaction in Entry 1 was carried out
by passing HBr gas into the alkene, using benzoyl peroxide as the initiator, appar-
ently near room temperature. Entry 2 is an example of anti-Markovnikov addition to
170
D. Elad and J. Rokach, J. Org. Chem., 29, 1855 (1964).
171 K. Griesbaum, Angew. Chem. Int. Ed. Engl., 9, 273 (1970).
172
N. A. LeBel, R. F. Czaja, and A. DeBoer, J. Org. Chem., 34, 3112 (1969); P. D. Readio and P. S. Skell,
J. Org. Chem., 31, 759 (1966); F. G. Bordwell, P. S. Landis, and G. S. Whitney, J. Org. Chem., 30,
3764 (1965); E. S. Huyser, H. Benson, and H. J. Sinnige, J. Org. Chem., 32, 622 (1962).