Transcript Alkyne Reactions

Alkyne Reactions

Addition

Substitution
 Diels-Alder
 Cleavage
Addition Reactions of Alkynes
Reduction to Alkanes
 Reduction to Alkenes

 Syn
addition via poisoned catalysts
 Anti addition via alkali metal/liquid
ammonia
Hydrogen halide addition
 Hydration - Ketone/Aldehyde
formation via tautomerization
 Halogenation

Alkyne Reductions
CH3 CH2 CH2 CH3
xs H2
Pt
H3 C C C CH3
H3 C
H2 /Pd/BaSO
4
Quinoline
(Lindlar's Catalyst)
Na
H
NH 3 (liq)
H3 C
H
H
C C
CH3
C C
CH3
H
Hydrogen Halide
Addition to Alkynes
Heteroatom stabilized carbocation
intermediates
H3 C C C H
H
H3 C C C H
X
HX
HX
H
H3 C C C H
+
H
+
H3 C C C H
X-
H
H3 C C C H
Markovnikov
addit ion
X
a vinyl halide
X-
X H
X H
H3 C C C H
X H
a geminal dihalide
H
H3 C C C H
X H
+
a heteroat om
stabilized carbocation
Hydration of Alkynes
Keto-enol tautomerization
H3 C C C H
H3 C C C H
H
+
H2 O/H2 SO4
H3 C C CH3
HgSO4
O
H
H3 C C C H
+
a vinyl cation
H2 O
H
+
H
H3 C C C H
H
H3 C C C H
H3 C C CH3
O
O
H
enol
ketone
OH
an enol
Halogenation of Alkynes
Formation of Vicinal tetrahalides
C C
an alkyne
X2
car bon
tetrachlor ide
X X
C C
X X
a vicinal tetr ahalide
Substitution
R
C CH
Na
R
+
+ H2
C C Na
Term inal
Alkyne
R
+
C C Na + R'CH 2 X
R
C C CH2 R' + NaX
Methyl
or
Primary
Alkyl
Halide
Alkynyl Anion Synthesis of Alkynes
via Bimolecular Nucleophilic
Substitution
Diels-Alder Reaction
C
C
C
C
C
 Six-membered
C
Ring formation (4+2)
 Diene + Dienophile
Cleavage Reactions of Alkynes
H C C H
R
C C H
ozonolysis
(r eductive workup)
ozonolysis
(r eductive workup)
ozonolysis
(oxidative workup)
H C C H
or
hot KMnO 4
R
ozonolysis
(oxidative workup)
C C H
or
hot KMnO 4
2 H C OH
O
R
C OH + H C OH
O
O
2 CO2
R
C OH + CO2
O