Methods in organic synthesis

1. METHODS IN ORGANIC SYNTHESIS

2. When olefins are treated with certain catalyst like complexes
of Mo or W or Ru, they are converted to other olefins in a
reaction in which the alkylidene groups have become
interchanged. This reaction is called metathesis of olefins.
Mo or W complexes with alkoxide and
imido ligands :Schrock catalysts
Ruthenium(II) carbenoid complexes :
Grubbs catalysts

3. General representation

4. Examples.....
 2-Pentene is converted to a mixture of about 50% 2-
Pentene, 25% 2-Butene and 25% 3-Hexene
CH3-CH2-CH=CH-CH3 W/Mo Complex CH3-CH2-CH=CH-CH2-CH3
+ +
CH3-CH2-CH=CH-CH3 CH3-CH=CH-CH3
 Dienes can react intermolecularly or intramolecularly

5. Continues.....
Cyclic olefins give dimeric dienes.
 The reaction between a cyclic olefin and a linear
olefin can give a ring opened diene.

6. Moreexamples..........

7. GRUBBS CATALYST
 Grubbs catalysts are a series of transition metal carbene
complexes used as catalysts for olefin metathesis.
 They are named after Robet H. Grubbs, the chemist who
supervised their synthesis.
 Grubbs catalysts tolerate many functional group in the
alkene substrates and are compatible with a wide range
of solvents.

8. First generation Grubbs catalyst
 Benzylidene-bis(tricyclohexylphosphino)-
dichlororuthenium
 It is synthesized from RuCl2(PPh3)3, phenyl
diazomethane, and tricyclohexylphosphine in a one pot
synthesis.

9. Second generation Grubbs catalyst
 It has the same uses in organic synthesis as the first
generation catalyst.
 The second generation catalyst has higher activity than
first generation catalyst.
 It is stable towards moisture and air.
1,3-bis-(2,4,6-trimethylphenyl)-2-
imidazolidinylidene]dichloro(phe
nylmethylene)(tricyclohexylphos
phino)ruthenium