Page 732 - Advanced Organic Chemistry Part B - Reactions & Synthesis

708 -bound species also react with a variety of organometallic reagents to give coupling
products.
CHAPTER 8
Reactions Involving CH 2 CHR
Transition Metals
Ar Pd II X RCH CHAr
RCH CH 2
Ar X+ Pd 0 Ar Pd II X
R′ M R′
Ar R′
Ar Pd II X

These are called cross-coupling reactions and usually involve three basic steps:
oxidative addition, transmetallation, and reductive elimination. In the transmetallation
step an organic group is transferred from the organometallic reagent to palladium.

oxidative addition R X + Pd 0 R Pd II X

transmetallation R Pd II X + R′ M R Pd II R′ + M X

reductive elimination R Pd II R′ R R′ + Pd 0

The organometallic reagents that give such reactions include organomagnesium,
organolithium, and organozinc compounds, stannanes, and even organoboron
2
2
2
compounds. The reactions are very general for sp -sp and sp -sp coupling and in
2
3
some systems can also be applied to sp -sp coupling. Most of these procedures
involve phosphine or related ligands.
Pd(L) y
R M + R′ X R R′
M = Li, MgX, ZnX, SnR , BR 2
3
Organopalladium intermediates are also involved in the synthesis of ketones and
other carbonyl compounds. These reactions involve acylpalladium intermediates, which
can be made from acyl halides or by reaction of an organopalladium species with
carbon monoxide. A second organic group, usually arising from an organometallic
reagent, can then form a ketone. Alternatively, the acylpalladium intermediate may
react with nucleophilic solvents such as alcohols to form esters.
O
C O II
R Pd
R C X O
Pd 0 II
R C Pd
R′ M R′OH
O R′
O
O
R C R′ R C Pd II
R C OR′
In considering the mechanisms involved in organopalladium chemistry, several
general points should be kept in mind. Frequently, reactions involving organopalladium