Page 317 - Advanced Organic Chemistry Part B - Reactions & Synthesis

4

Electrophilic Additions

to Carbon-Carbon Multiple

Bonds

Introduction

Addition of electrophilic reagents is one of the most general and useful reactions
of alkenes and alkynes. This chapter focuses on reactions that proceed through
polar intermediates or transition structures. We discuss the fundamental mechanistic
characteristics of this class of reactions in Chapter 5 of Part A, including proton-
catalyzed additions of water and alcohols and the addition of hydrogen halides. Other
electrophilic reagents that we consider there are the halogens and positive halogen
compounds, electrophilic sulfur and selenium reagents, and mercuric salts. Hydrobo-
ration is another important type of electrophilic addition to alkenes. In the present
chapter, we emphasize synthetic application of these reactions. For the most part,
electrophilic additions are used to introduce functionality at double and triple bonds.
When the nucleophile addition step is intramolecular, a new heterocyclic ring is formed,
and this is a very useful synthetic method.
E + E + E
(C) n E
or (C)
(C) n (C) n
Nu n Nu
Nu: Nu:
exo – cyclization endo – cyclization
Carbonyl compounds can react with electrophiles via their enol isomers or equivalents,
and these reactions result in -substitution.
δ + δ −
O OH O
X Y
R′ CH R R′ CHR R′ CHR
2
X
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