2. SUZUKI REACTION
In 1979,A. Suzuki and N. Miyaura reported a stereoselective synthesis of
Arylated (E)-alkenes by cross-coupling reaction between organoboron
compounds with organic halides or triflates
This palladium-catalyzed cross-coupling reaction that forms carbon-carbon
sigma bond and known as Suzuki cross-coupling reaction (Commonly used
for synthesizing biaryl compounds)
GENERALSCHEME
5. MECHANISM
STEP1 – OXIDATIVEADDITION - The rate determining step of the catalytic
cycle in which an organic halide couples to the Palladium catalyt to form
organopalladium complex[Pd(0)-species to form Pd(II); as two groups add to the
metal]
STEP2 – Exchange of the anion attached to the palladium for the anion of the
base; Hydroxide attacks Pd, kicking off X
6. STEP 3 – TRANSMETALLATION - Lewis base (OH⁻) attacks the Lewis acid (B)
These Pd(II) and the alkylborate complex state is most unstable and thus it will
remove the R group(carbon); thus Carbon attaches to a metal because of closer
electronegativity
Electronegativity values: C=2.5, B=2.0, Pd=2.4
7. STEP4 – Reductive elimination- The final step that forms the C-C sigma
bond and also regenerates the Palladium catalyst[ Pd(0) ] so that it can
participate again in catalytic cycle
The order of reductive elimination is as follows :Ar-Ar >Ar-R > R-R
8. SHAPIRO REACTION
Discovered by Robert H. Shapiro in
1967
Involves the base catalysed
decomposition of tosyl hydrazones
of aldehyde and ketones (having
alpha hydrogen) into olefins by
reacting with organolithium
compound as base (usually two
equivalent of MeLi or BuLi) in
ether, hexane, or
tetramethylenediamine
carried out at -78°C
9. MECHANISM
Deprotonation of –NH proton from aryl sulfonyl hydrazone happens, reaction of
tosylhydrazone with a strong base (usually metal-alkoxides) results in the
formation of a diazo compound
In case of Shapiro reaction, two equivalents of alkyllithium reagent deprotonate
the tosylhydrazone both at the nitrogen and the α -carbon and an alkenyllithium
intermediate is formed via a carbanion mechanism. The protonation of the
alkenyllithium gives rise to the alkene
