Organic Chemistry – The Functional Group Approach
Br
OH
alkane
(no F.G.)
alcohol
halide
alkene
non-polar (grease, fats)
polar (water soluble)
non-polar (water insoluble)
non-polar (water insoluble)
tetrahedral
tetrahedral
tetrahedral
trigonal
O
NH
alkyne
aromatic
aldehyde/ketone
imine
non-polar (water insoluble)
non-polar (water insoluble)
polar (water soluble)
polar (water soluble)
linear
flat
trigonal
trigonal
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Organic Chemistry – The Functional Group Approach
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Carey Chapter 10 - Conjugation in Dienes and Allylic Systems
H
H
H
H
H
H H
CH3
H
H
OH
H
H
H H
OH
10.1 The Allyl group
Br
H
H H
Br
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10.2 - Allylic Carbocations
Figure 10.1
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10.3 - SN1 Reactions of Allylic Halides
Allylic system reacts 123 times faster
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10.3 - SN1 Reactions of Allylic Halides
via
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10.4 - Allylic Free Radicals
Figure 10.2
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10.5 Radical halogenation at allylic positions is possible
Usual radical process steps are involved;
Initiation, Propagation and Termination
Intermediate radical is stabilized by resonance
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10.6-10.8 - Classes of Dienes
1,4-pentadiene
1,3-pentadiene
Figure 10.2
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10.8 - Conformations of Dienes
Conformers, not
isomers
H
H
H
H
H
H
H
H
The conformers are interconvertible
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10.8 - Conformations of Dienes
Some trapped as
s-cis
O
Some trapped as
s-trans
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Conformations of 1,3-butadiene
H
H
H
H
H
H
H
Figure 10.5
H
The s‐cis and s‐trans conformers are interconvertible with an ~3.9 kcal/mol barrier
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10.9 - Bonding in 1,2-propadiene (allene)
Figure 10.6
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10.9 - Bonding in 1,2-propadiene (allene)
Figure 10.6
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10.10 - Preparation of Dienes
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10.11 - Addition of HBr
to 1,3-Butadiene
Br
HBr
Br
+
-80oC
H
H
81%
2
Br
HBr
1
4
3
19%
Br
+
room temp
H
H
44%
56%
Br
HBr
45oC
Br
+
H
H
15%
85%
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Thermodynamic and kinetic control in addition of HBr to 1,3-butadiene
Figure 10.8
Addition of HBr is reversible so at higher temps the equilibrium outcome will favour the more stable product. Lower temp. reduces ability of products to revert to cation so the kinetic outcome is then favoured.
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10.13 - The Diels-Alder Cycloaddition Reaction
Diene
Dienophile
Lowest unoccupied molecular
orbital of diene
Highest occupied molecular
orbital of dienophile
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10.13 - The Diels-Alder Cycloaddition Reaction
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10.13 - The Diels-Alder Cycloaddition Reaction
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10.13 - The Diels-Alder Cycloaddition Reaction
Total Synthesis of Minfiensine
MacMillan, Jones, Simmons. JACS, 2009
Discussed at www.totallysynthetic.com
Total Synthesis of Vinigrol
Baran, Maimone, Shi, Ashida. JACS, 2009
Discussed at www.totallysynthetic.com
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Not covering
10.14
10.15
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