Carbene Addition to C=C Bonds

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Carbene Addition to CC Bonds
Generation of carbenes
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Electronic Structures of Carbenes
q
q
arylcarbenes cycanocarbene alkynylcarbene
CF2 CCl2 CBr2 CHCO2R
CH2 (q' gt q)
100110
130150
cis-olefin
cis-cyclopropane
Retentive stereochemistry
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spin inversion
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Orbital Interaction Between Carbene and Olefin
gt more stable
asymmetrical transition state
symmetrical transition state
Reaction of Conjugate Dienes (cisoid) with
Singlet Carbenes
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pp and sp interactions between singlet
carbenes and olefins
reactive both to electron rich and deficient
olefins
Electrophilic
nucleophilic
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Typical carbene reactions
a-elimination
Ph
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a-elimination
insersion
Reimer-Tiemann reaction
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Nitrene
isocyanate
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Electrophilic organometallic reagents
the carbon-metal bond highly polarized
the carbon-halogen bond highly polarized
Simmons-Smith Reagent
Carbene Metal Complexes
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Carbenoids Electrophilic and Nucleophilic
Properties
nucleophilic
carbenoid
electrophilic
carbenoid
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The first catalytic asymmetric reaction of
prochiral compounds caused by soluble chiral
metal complexes Nozaki, H. Moriuchi, S. Takaya,
H., Noyori, R. Tetrahedron Lett. 1966, 5239
?-?????? (Simmons-Smith)
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Alkene metathesis
Mechanism
2 2
metallacyclobutane
Metal-carbene complex
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Evidence supporting Chauvin mechanism
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Addition of Radicals to CC Bonds
without peroxide
Markovnikov rule carbenium ion stability
Ionic process
hyperconjugation
with peroxide
anti-Markovnikov rule radical stability
radical process
Mechanism radical chain process
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Gomberg, 1900 "persistent hydrocarbon radical"
"persistent hydrocarbon radical"
radical with shelf-storable stability
LUMO of acceptor
SOMO of radical
DPPH
HOMO of donor
capto-dative radical
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Some previous observations difficult to explain
.
fast
.
.
minor
major
slow
Recent findings to explain these previous issues
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Reasonable explanation for alternative
co-polymerization Why the reaction proceeds in
such a way?
Polymer)n
Polymer)n1
Favorable orbital interactions are highly
specific !!
LUMO
LUMO
SOMO
SOMO
HOMO
HOMO
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Structures of Radicals